Home

remote afterloading technology - The American Association of

1. radiation detector and indicator remote afterloader storage position panen bed remote afterloader treatment position door interlock viewing window GZ radiation Y Z indicator Z also indicated at nursing station area Figure 3 A dedicated LDR remote afterloading room with a small maze entryway and viewing window Modified from B M Wilson et al Med Phys 13 608 1986 courtesy of J D Bourland Rochester MN 24 given to its features and location An audible alarm is undesirable a continuously flashing light that indicates the source s is out of unit should be located such that it is viewed by those entering the room but visually shielded so it does not disturb the patient Viewing of the patient is generally through a window in the maze wall Figure 3 or by remote video camera with monitor located at the nurses station Most LDR units feature a remote system status indicator with audible and visible indicators to allow nurses to monitor treatments Often an audible repeating beep that indicates therapy is underway is an unacceptable distraction to the nurses working at the work station Special attention is required for electrical power outlets the LDR unit should be on a dedicated circuit as well as on the facility s emergency power circuit A power conditioner may be required to stabilize incoming power An adequate number of electrical outlets must be availab
2. The calibration of the radioactive source s and dosimetry are addressed in a later section 42 A Remote Afterloader Tests Acceptance testing of the mechanical and electrical functions of the remote afterloaders includes but is not limited to confirming 1 That all console functions key switches main power battery power source ON OFF door OPEN CLOSE etc and indicators perform properly 2 That the source s retracts at the end of preset times retracts when interrupted retracts under loss of electrical power or air pressure if so driven retracts if source guide tubes or applicators are connected in an improper sequence improperly connected constricted or blocked and retracts when the emergency button s is used Confirm appropriate console displays or printed tape error messages by producing or simulating a planned failure or error Confirm that programmed data duration of remaining treatment time etc is retained if source retraction or other unplanned interruptions occur 3 The battery voltage under load is adequate and that operating functions retained under battery power indeed work 4 The accuracy of timers relative to an independent clock for periods similar to those proposed for treatments determine end time effects End effects may not be a medically important parameter for LDR units or HDR units but may be a consideration during certain source calibration procedures particularly tho
3. An Unusual Afterloading Malfunction with a Curietron Assoc Med Phys India Bulletin 10 212 1985 R D Young Safety Considerations For Remote Afterloaders Med Phys 16 495 1989 Abstract C A F Joslin C W Smith and A Mallik The Treatment of Cervix Cancer using High Activity Co Sources Brit J Rad 45 257 270 1972 H Newman K W James and C W Smith Treatment of Cancer of the Cervix with a High Dose Rate Afterloading Machine The Cathetron Int J Radiat Oncol Biol Phys 9 931 937 1983 Y Shigematsu K Nishiyama N Masaki T Inoue Y Miyata H Ikeda S Ozeki Y Kawamura and K Kurachi Treatment of Carcinoma of the Uterine Cervix by Remotely Controlled Afterloading Intracavitary Radiotherapy with High Dose Rate A Comparative Study with a Low Dose Rate System Int J Radiat Oncol Biol Phys 9 351 356 1983 L Mandell D Nori L Anderson and B Hilaris Postoperative Vaginal Radiation in Endometrial Cancer Using a Remote Afterloading Technique Int J Radiat Oncol Biol Phys 11 473 478 1985 97 26 27 28 29 30 31 32 33 T Teshima M Chatani K Hata and T Inoue High Dose Rate Intracavitary Therapy for Carcinoma of the Uterine Cervix I General Figures of Survival and Complication Int J Radiat Oncol Biol Phys 13 1035 1041 1987 Y Akine H Arimoto T Ogino Y Kajiura I Tsukiyama S Egwa T Yamada K Tanemura R Tsunematsu K Ohm
4. Remote Afterloading Compared to Manual Afterloading Brachytherapy Administrative Radiol 9 61 69 1990 100 49 50 51 52 33 54 55 56 bye IEC Particular Requirements for the Safety of Remote Controlled Automatically Driven Gamma Ray Afterloading Equipment International Standard IEC 601 2 17 89 Medical Electrical Equipment Part 2 Bureau de la Commission Electrotechnique International Geneva 1989 L F Mesina G A Ezzell J M Campbell C G Orton Acceptance Testing of the Selectron High Dose Rate Remote Afterloading Cobalt 40 Unit Endocurietherapy Hyperthermia Oncology amp 253 256 1988 P W Grigsby Quality Assurance of Remote Afterloading Equipment at the Mallinckrodt Institute of Radiology Selectron Brachytherapy Journal 1 15 1989 A Flynn Quality Assurance Checks on a MicroSelectron HDR Selectron Brachytherapy Journal 4 112 115 1990 C H Jones Quality Assurance in Brachytherapy Using the SelectronLDR MDR and MicroSelectron HDR Selectron Brachytherapy Journal 4 48 52 1990 E D Slessinger A Quality Assurance Program for Low Dose Rate Remote Afterloading Devices in Brachytherapy HDR and LDR edited by A A Martinez C G Orton R F Mould Nucletron Corp Columbia MD 1990 160 168 G A Ezell Acceptance Testing and Quality Assurance of High Dose Rate Remote Afterloading Systems in Brachytherapy HDR and LDR edited by A A M
5. quality assurance procedures which may change over time should be excluded from the license if possible to allow the user some flexibiity in developing a strong useful quality assurance program The regulatory agency may be particularly interested in independent verification of planned treatments and other pretreatment quality assurance procedures due to recent misadministrations with remote afterloading units License compliance requires timely compliance with and thorough documentation of each item in the license that requires a written record Particular forethought must be given as to how these written records will be maintained to prove compliance during regulatory inspections V RADIATION CONTROL SAFETY To write the license application requires that radiation control procedures be developed prior to the license application Regardless of the type of remote afterloading unit radiation control procedures generally can be grouped into 1 safety features inherent in the remote afterloading unit 2 initial radiation survey of the facility and subsequent patient surveys 3 routine precautions required during normal use 4 precautions required during source exchanges 5 emergency procedures 6 training and retraining of personnel A Design Safety Features AU remote afterloading units should have certain safety features some of which are listed in Tables 1 and 2 These include but are not limited to 1 A back up b
6. Bladder and Rectal Dosimetry MINIRAD Isotopest Technik GmbH Germasy Low Interstitial 1 6mm to 8mm Some magnetically connect to drive cables None static No 16 in unit 16 in containers No Conventional interstitial needles Heyman applicators Not stated in commercial literature Use preloaded seeds in ribbons to give desired distribution is has dedicated RTP software Low Intracavitary Interstitiat intraluminal Sources mechanically connect to drive cables None static Back up battery 30 in vnit No Conventional interstitial needtes Not stated in commercial literature Use preloaded seeds in ribbons to give desired distribution 11 OMNITRON 2000 MicreSelectron QMNITRON POR Use USA Hi Low Medium ieh variable Intraluminal Intratuminal Interstitial Interstitial Intracavitary Intracavitary Smallest 20 gua 0 89 mm neea Source permanently Source laser welded to connected to stainless drive cable steel cable Stepe cource in Stepping motor 48 11 mm increments steps of 25 mm over over L 12 cm length 48 steps of 5 0 mm over 24 cm length Back up battery Dual monitors and mechanical crank battery tgency hand crank In unit up to 12 Ci 1 0 Ci source Ir Yes Yes Interstitial needies Flexible amp rigi numerous catheters needles bronta imtracavitary gt imm lmm Stepe dwell times Point source at 48 used to achieve positi 2 5 mm desired
7. It is imperative that the user understand the algorithms and various input parameters and factors the RTP computer uses for the dose calculations For example while representation of a small linear high activity source as a point source is common practice one prefers the computer algorithms to correctly represent the anistropy of the source If the anisotropy of the source capsule cannot be modeled by the RTP computer the user must understand how the calculated dose distribution for the point source differs from the true dose distribution around the source In arrays of sources the attenuation and scattering of the adjacent active source pellets or inactive spacers should be represented but this may be difficult using conventional RTP software Dedicated software provided by the vendor may offer a better representation of single source or multiple source dosimetry than the conventional RTP software used to represent seed and linear sources as one presumes the vendors best know their own sources and how to represent them However conventional RTP computer vendors are now including special algorithms in upgrades to their software to represent remote afterloading sources Attenuation of applicators used for the Selectron the Gamma Med Ili and the Selectron HDR have been reported Computer generated isodose curves should clearly state if applicator effects have been included or neglected in the computation Tissue attenuation
8. Medium High Intracavitary Checks and confirms nucropmcessor 10 or 20 Cs Capsules in train 20 3 mm x 2 65 mm OD 500 or 1000 mCi b Radiosotope Physical Size Radioisotope Physical Size Activity Capsufe not stated Capsule 2 4 mm L x demm OD to Ci MicroSelectron LDR Nucletron Enginerring BV Netherlands Low intraluminal Interstitial Intermediate Safe WCs 1 Ci Ir Ci Mobile Safe WCs 3 Ci mir 15 Ci None 15 45 wires or ribbons 15 Cs Mini seeds up to 140 mm L x 08 mm OD in 1 3 mm OD train S nCi seed Ribbons wire seed up to 140 mm L x 1 1 mm OD selected by user Seleetron LDR Nuctetron Engineering BV Law Medium Intracavitary Cs 2 2 Ci Pneumatic checks of source positions 3or6 AR 3orh Es Pellets 25 mm 10 to 40 mCi per terres arta tet ee a Nt ee Perpe 10 Table 1 b Low Medium and High Dose Rate Remote Aftertoading Devices Maaafactucer or Vendor L 10 n 12 13 14 Dose Rates Modality Outside Diameter of Applicators Method of Source Transfer Method of Source Movement Method of Source Retraction in the Event of a Failure Storage of Source Simulation Sources for Treatment Simulation Applicators Apep Accu of Source Position Source Arrangements and kutation Uses Conventional RTP Software or Dosimetry Dose Optimiza tion Table
9. circuit TV and patient intercom work that radiation monitors door interlocks and warning lights work that batteries are charged and that the unit operates properly during a simulated or test therapy session Source positioning accuracy can be determined by directly viewing by CCTV the source moving through a transparent scaled applicator so that source position can be determined visually with millimeter accuracy Figure 9 To confirm desired program sequence to produce a given source arrangement test devices with multiple treatment channels Figure 8 can be used with films to produce by autoradiography the planned source arrangement Any computer decayed source activity should be checked against a pre calculated decay chart to confirm the unit has decayed source activities accurately In a facility with only a few patients a year all quality assurance tests can be done the day prior to or on the day that the remote afterloading unit is scheduled for use rather than daily or weekly Should the Ir sources in remote afterloaders be checked to confirm proper source decay There is a short lived Ir isotope that could be an undesired contaminant in a Ir source However a 10 uncertainty in the half life of Ir 73 8 7 4 days provides only a 3 uncertainty in decayed source activity at thirty days A 10 uncertainty in the half life of Ir caused by an excessive amount of Tr in the source capsules is highly unlikely as
10. that the sources will transport as planned to l mm accuracy to preselected locations 4 That the radioactive source s move accurately through the applicator s creating the desired radiation dose patterns Visual verification Figure 9 via CCTV and or radiographs of simulated sources at numerous planned locations in test devices or in the applicators followed by autoradiography on the same film are required 5 The radiation attenuation of applicators and deciding if attenuation corrections will be made in treatment planning D Source Tests Acceptance testing of the radioactive source s will include 1 A careful review of the source s certificate regarding physical and chemical form source encapsulation and model number to confirm that the source s delivered complies with those allowed 46 b Autoradiograph of HDR source superimposed on the radiograph Note the non coincidence of the dummy and live source positions caused by failing to push the dummy source fully to the end of the catheter N B Simulator field delineator wires should be removed from the field so they do not obstruct the images that was not done here Courtesy of G P Glasgow Maywood IL 47 Figure 6 c Vertical lines mark the center of every alternate dummy seed allowing measurements of the distances between the dummy seed centers and the centers of the radiation patterns produced by the live source d Pen pricks in the film at
11. Compliance 30 A Licensing Agencies 30 B License Contents 31 C License Compliance 32 V Radiation Control Safety sees s isessssssssseesssrrrsssssssseressrrrenssssssne 33 A Design Safety Features ss isesessssssserriirrressssssstrrrrrrrersssssn 33 B Radiation Surveys oaren a a RE RKR REAREN KERNE 34 C Routine Precautions s eeeesssssssserrreeerssesssssetereeerssesssssoerreeres 34 Dy Marital s iecsat acces ieaie yy 37 E Source Exchange Procedures 39 F Emergency Procedures 40 G Training Courses iarere e E 41 VI Acceptance Tests sscscssseceseserersesseseseessenesessesseseseeseessenseneseees 42 A Remote Afterloader Tests csssecsssecseecsesecesecseesseneeteneetenes 43 B Facility Testing sccsssssssssssssseesssessessnseseessnneessesnnteceesneeesens 44 C Source Transport Systems and Applicator Tests 45 D Source Tests icscasiiscnnaiscsncnisensacennnicannanincnimenie 46 E Brachytherapy Planning Computer 57 VII Quality Assurance a 88 A Equipment Location n eececssecssecssesssesssessnessuessseessseensee 58 B Frequency and Type of Equipment Quality Assurance Tests sssesessseseensesesssensessesneensesseense 59 TABLE OF CONTENTS PAGE C Quality Assurance in the Use of Equipment 61 VII Source Calibrations ccccscssessssesscssesssssescsssssesseeesessessseeesesseeseers 62 A Source Certrficates s lt cssccescconceveccasccvecsasecesvcivessvestse
12. II Source Calibration Employing Ionometric Techniques in Proceedings of Second Annual International High Dose Rate Remote Afterloading Symposium Health Physics Consultants South China Maine 1987 75 81 National Council on Radiation Protection and Measurements Report 91 Recommendations on Limits for Exposure to Ionizing Radiation National Council on Radiation Protection and Measurements Bethesda MD 1987 International Commission on Radiological Protection Publication 60 1990 Recommendation of the International Commission on Radiological Protection Annals ICRP 21 1991 United States Nuclear Regulatory Commission 10 CFR 20 1301 a 1 Federal Register 56 No 98 Tuesday May 21 1991 J D Bourland M A Varia G W Sherouse P E Stancil L D Stanley E L Chaney H L McMurray J E Tepper Incorporation of Emerging Technology into the Design of a Radiation Oncology Facility Problems Encountered Phys Med Biol 33 Supp 1 55 1988 Abstract A L McKenzie J E Shaw S K Stephenson P C R Turner eds Institute of Physical Sciences in Medicine Report 46 Radiation Protection in Radiotherapy Institute of Physical Science in Medicine London 1986 E E Klein P W Grigsby J F Williamson A S Meigooni Pre installation Empirical Testing of Room Shielding For HDR Remote Afterloaders Med Phys 18 655 1991 Abstract P W Grigsby and C A Perez The Cost of Low Dose Rate
13. Ir Sixty steps are available with incremented steps of l to 10 mm for a maximum length of 300 mm The Curietron intracavitary HDR unit uses static Cs capsules in source trains of desired lengths inactive spacers are loaded to form source trains of the desired active lengths The projector can contain up to 185 GBq 5 Ci of Cs and uses four sources at once Numerous conventional GYN applicators Fletcher Henschke etc are available as are plastic applicators of the DeLouche or Chassagne type The Curietron 192 HDR unit is designed for interstitial treatments and uses a shifting mechanism that can move a 370 GBq 10 0 Ci Tr source over 64 cm using thirty two steps The unit has twenty treatment channels The MicroSelectron HDR features 4 5 mm long by 1 10 mm diameter Tr capsule with an eighteen channel indexer it is designed for use with either interstitial or gynecologic applicators The unit moves a 370 GBq 10 0 Ci Ir source over 12 cm using forty eight positions separated by 2 5mm or over 24 cm using forty eight steps of 5 mm 18 The Selectron HDR is designed for intracavitary and intraluminal treatments and contains twenty Co pellets with a total activity of 370 GBq 10 0 Ci The unit is available with three channels The Gamma Med II an intracavitary unit features a 740 GBq 20 0 Ci Ir source that is moved by a stepping motor over the 20 cm length of an applicator steps of either 0 5 cm or
14. and multiple scattering either r or F r 8 often are options in isodose curve computation with several recipes available As previously discussed the user should have investigated the various models available and adopt one best suited for the source design used 93 Many remote afterloading sources are not static they can move and the combination of possible multiple source positions and different dwell times at these positions occuring in numerous catheters in a patient is a formidable isodose computation problem particularly for planning calculations Dose optimization software using non linear regression analysis techniques limited by stated boundary conditions affords one solution to this problem Anderson describes a non linear regression approach to calculating the dose for a Ir source that steps along a single channel applicator Such non linear regression optimization methods now are available on most computer systems supplied with remote afterloading devices 94 REFERENCES 1 P R Almond Remote Afterloading in AAPM Monograph No 9 Advances in Radiation Therapy Treatment Planning edited by A E Wright and A L Boyer American Institute of Physics New York 1983 601 619 2 R F Mould ed Brachytherapy 1984 Proceedings of the Third International Selectron Users Meeting Nucletron Trading BV Leersum The Netherlands 1985 3 R F Mould eds Brachytherapy 2 Proceedings of the 5th Intern
15. assist with and confirm applicator placement provisions for anesthesia medical gases special lighting treatment tables and storage of these items when not in use Careful planning with departments that provide these services will be required because there are often emergency care reasons or other hospital policies that preclude anesthesia performed anywhere other than the primary operating rooms If anesthesia and diagnostic x ray equipment are not located in the actual LDR treatment suite forethought regarding where these procedures are to be performed is required Finally a cable pass for dosimetry calibration equipment is useful to allow source calibrations and quality assurance dosimetry procedures to be performed from outside the treatment room C Facility Design High Dose Rate Units The features of an HDR therapy suite will depend on the anatomic sites to be treated the annual number of patients the radiation oncologists philosophies and treatment regimens the space available and the availability of funds Instantaneous dose rates around HDR units with 370 GBq 10 0 Ci sources preclude their use in conventional rooms unless patients are placed in specially designed local shielding areas or devices within the room The size of a dedicated HDR vault often is determined by the amount of ancillary x ray imaging equipment installed A small vault 55 m 18 by 5 5 m 18 will generally require 60 cm 2 thick concre
16. brachytherapy in numerous anatomic sites A Advantages of Remote Afterloading Remote afterloading improves radiation control and provides technical advantages such as isodose distribution optimization that improve patient care Replacing manual afterloading with remote afterloading reduces the radiation exposure to radiation oncologists physicists attending physicians source curators nurses and other allied health personnel Remote afterloading is an application of the As Low As Reasonably Achievable ALARA principle in radiation control The decision by the United States Nuclear Regulatory Commission to adopt ALARA as a license requirement for by product materials licenses rather than as a voluntary committment is a motivating factor for purchasing remote afterloading units Remote afterloading offers less probability of temporarily misplacing radioactive sources or actually losing sources events that do occur with manual afterloading Nurses caring for patients treated with an LDR unit one in which conventional doses of about 10 Gy are delivered daily for several days can retract radioactive sources as required to provide more nursing care with less fear of radiation exposure An LDR unit in a dedicated room eliminates the undesirable practice of assigning patients to different rooms in the hospital so that one group of nurses will not care for all implant patients With a dedicated room containing an LDR unit a s
17. costs of a remote afterloading facility are given by l r xr l r 1 x Capital Costs 1 where ris the annual discount or depreciation rate and n is the number of years Capital costs generally consist of the equipment cost long lived radioactive sources room modification expenses ancillary equipment but would exclude annual costs of service contracts personnel salaries and short lived radioactive sources For example for a low dose rate unit that costs 128 000 with room modification costs of 59 000 the annualized cost for ten years at 10 is about 30 000 Low dose rate remote afterloading generally is more expensive than manual afterloading Grigsby estimated that procedure costs for LDR brachytherapy were at least 25 greater than the costs of similar manual brachytherapy procedures IV LICENSES AND LICENSE COMPLIANCE A Licensing Agencies Purchasers of remote afterloading units must apply for a license or license amendment with the appropriate regulatory agency either an Agreement State agency or the United States Nuclear Regulatory Commission for non Agreement States and for federal hospitals The purchaser should always ask the vendor to prove by supplying a copy of the registration that the device and sources are on the Registry of Radioactive Sealed Sources and Devices Equipment not on this Registry cannot be licensed license applications can be delayed for many months while the vendors attempt to place new de
18. distance care must be exercised in making all appropriate conversions to the measured quantity for comparison to the parameter stated on the certificate AAPM Report 21 is a useful guide The apparent activity A follows from X F C x Anne t R s 3 Ax XP T x Bq p4 82 Where G is the exposure rate constant for an encapsulated source with a specific wall thickness G traditionally expressed in Recm hemCi must be converted to Rem Bqes to maintain consistent nit notation in 13 and 14 A is the apparent activity of the source Alternately the apparent activity A follows from Kul ner Cade Gy s _ BS Awe Kul P d Bq 6 where G is the air kerma rate constant in Gyem Bqes for an encapsulated source with a specific wall thickness Tix Ck W ate Gy m Baes 17 In equations 13 17 one should use the manufacturer s selected values for G or G with careful attention to the units as these were the values used by the manufacturer in obtaining A for the certificate e The factor M in equation 11 is the charge collected per unit time with the source at a fixed calibration distance from the chamber M should not include charge collected during source transit There are several ways to correct M for the transit charge If a timer other than that of the remote afterloader is available to start and stop charge integration while leaving the final reading frozen on
19. dose it OF 5 mm apart distribution seconds in 0 1 second increments Pulsed variable 10 minutes up to 4 hours Yes or dedicated planning systems Features dedicated RTP system Yes 300 optimizati points on Yes Tabte 1 b Cont d Low Medium and High Dose Rate Remote Afterloading Devices Manufacturer or Vendor Dose Rates 2 Modality Source Container Maximum Storage Activity 16 Special Features 17 Number of Applicator Channels 18 Maximum Number of Sources in Projector 19 Maximum Number of Channels Used Simultancousty SOURCES a Radioisotope Physicat Size b Radiosotope Physical Size Radioisotope Physical Size Activity TNIRAD Isotopen Techaik Dr Saverwein GmbH Germany Low Interstitial Not stated Allows sequential loading of several patients 6 16 16 ir oye me Seeds in ribbons dimensions unspecified Inter Pal Inter Pal GmbH Gennany Low Intracavitary Interstitial Intraluminal Not Stated L infrared remote controller for source transfers mye Ribbans 0 7 to 3mm OD length unspecified Conventional activities 12 OMNITRON 2000 OMNITRON Corporation USA High MicroSelectroa PDR Nucletroa Corporation USA Low Medium vacizble Intraluminal Interstitial intracavitary r 2 Ci Intraluminal Interstitial Intracavitary mIn 12 Ci Small source size Memor
20. known locations 5 cm intervals from the catheter tip allow measurements of the live source radiation patterns relative to the end of the catheter Courtesy of G P Glasgow Maywood IL 48 Figure 7 Device used for autoradiography to test source positioning accuracy a Plastic jig with drilled pin holes to indicate the physical position of sources on autoradiographs Courtesy of G A Ezzell Detroit MI 49 Figure 7 b Three pin holes made in the film and joined by a line pass through the source s center on the autoradiograph Courtesy of G A Ezzell Detroit MI 50 Figure 8 a An eighteen channel autoradiography test device Courtesy of G A Ezzell Detroit MI 51 Figure 8 b Autoradiograph obtained using the device Courtesy of G A Ezzell Detroit MI 52 Figure 9 a A visual alignment source position test device Mick Radio Nuclear Inc New York modified by adding a diode to check source activity Courtesy of J Meli New Haven CT 53 apanda tiha Figure 9 b A visual alignment source position test device Courtesy of Miles Mount Nucletron Corp Columbia MD 54 under the license A source design drawing should be available as details of source s construction may be required for computer models of the source s and the resulting radiation dose distribution 2 Determination of correct number of and the relative activities for multiple sources of the sa
21. o r for the spherical Cs sources in the Selectron have been reviewed and investigated by Almond et al Siwek et al and Grigsby et al who report on applicator effects as well Pla et al investigated dose distribution of HDR Co pellets in Selectron applicators Meli et al measured a r for a Ir HDR source Cerra and Rodgers measured source anisotropy F r 8 for Ir Gamma Med sources including additional anisotropy introduced by certain applicators Figure 10 Park and Almond observed that the Meisberger et al coefficients were superior to the Van Kleffens and Star coefficients in describing absorption and scatter along the transverse axis of a Ir source in a Selectron HDR unit Since the anisotropy factor F r is dependent on source design users of remote afterloading units should carefully review the literature before adopting any specific set of values for calculation of dose distributions 5 Calibrations in water or solid phantoms Calibrations in water or in solid phantoms of water equivalent material allow potentially more reproducible measurements over time relative to in air measurements as positioning errors may be less in a well designed water or solid phantom than with in air calibration devices Any phantom must be sufficiently large to provide full scatter in all directions Meli et al investigated the dosimetry characteristics of polystyrene solid water and polymet
22. procedures Table 3 will require operating room features such as medical gases overhead operating room lights anesthesia equipment and overhead radiographic and fluoroscopic x ray tube all in support of bronchoscopy esophageal cervical and other applicator placement procedures Generally construction costs per patient will be high unless a large number of patients are treated annually If an existing teletherapy or linac vault is used the radiological safety features listed are still required While most vaults possess adequate shielding for 370 GBq 10 0 Ci Ir 192 sources a vault survey with a source of the activity and type proposed will confirm the adequacy of the vault and identify hot spots or shielding defects Special care is required to ensure that the teletherapy unit or linac cannot be turned on while a HDR procedure is underway usually this can be achieved by using interlocks One simple procedure keeps operating keys for both units on a single key ring with no duplicate keys available at the units It is usually difficult to add minor procedure equipment to an existing vault Usually an adjacent simulator room can be used for applicator placements and localization procedures and can be modified as a minor procedure suite The major disadvantage using an existing teletherapy vault is scheduling patients for remote afterloading procedures in a vault used for external beam patients 29 D Costs Annualized
23. ratio of the dose rate in a full scattering medium to the dose rate to an equilibrium mass of tissue located at the same point in free space This accounts for absorption and scatter by the medium In the terminology of Meisberger et al the tissue attenuation factor is given by r F r 7 2 21 and accounts for absorption and scatter along the transverse axis While there are many reports of measurements of radial dose distributions for radioactive sources the equations and parameters in Tables 6 and 7 have been widely verified for conventional sources used in manual afterloading procedures For conventional low activity seed sources likely to be used in remote afterloaders o r or closely related values have been reported for Ir seeds and Cs seeds by Meisberger et al by Thomason and Higgins and for Ir seeds by Meli et al and Weaver et al 89 90 Table 6 Some mathematical models accounting for attenuation and multiple scattering in a medium surrounding a radioactive source REFERENCE MODEL amp DEFINITIONS Meisberger Xw Xa A Br Cr Dr et al ce Xw Exposure in water Xa Exposure in air r Distance in cm from source to point of calculation A B C D Zero first second and third order polynomial fitting coefficients Van Keffens f d 1 ad 1 bd and Star a a d Distance in cm from source to point of calculation a b Second order coefficients L L M
24. the effective energies based on the half value layers of the photon beams and the Ir value obtained by interpolation at 300 kV As a practical matter most 250 kV x ray chamber calibrations are usually performed without a cap before using any existing 250 kV x ray chamber calibration point users should review the calibration certificate carefully to determine if the build up cap was present or absent during calibration Goetsch and Attix originally recommended that ionization chambers intended for use with Ir gamma ray sources be calibrated instead with Cs gamma rays and moderately filtered 250 kV x radiation and the two calibration factors be averaged Both calibrations were performed with a chamber wall including cap having a minimum 69 thickness of 9 3 x 10 electrons cm e g 0 31 g cm graphite The same wall including cap thickness must then be used for Tr measurements More recently Goetsch et al described a procedure to interpolate between rather than average the Cs and 250 kV calibration points Nde 1 DAN a Nded 2 R C 2 x 0 0037 t 9 3 x 10 3 where N rx ny a denotes the calibration factors in roentgen per coulomb for Tr 2 50 kV x rays and Cs respectively t denotes a wall plus cap thickness expressed in electrons cm 9 3 x 10 is the number of electrons em in 0 31 g cm of graphite 0 0037 corrects for attenuation by a wall plus cap thickness of 0 31 g
25. the electrometer s display integration can begin after the source has reached its calibration location and terminated before the source returns to the safe In this case M is the total charge collected divided by the total time Goetsch et al achieved this with an electronic timer rigged to trigger a pulse to start and stop an electrometer Care must be taken to avoid including any transient charge collection associated with the opening of the electrometer input if that event defines the start of the time interval A programmable electrometer such as a Keithley Model 617 can be programmed to 83 record store and display data at predetermined time intervals Otherwise a stop watch may be used to measure the time between two voltages displayed by the output digital voltmeter If the remote afterloader timer is used not recommended corrections must be made for the charge collected during source transit end effect or timer error Ezzell used standard techniques developed for shutter timing errors to measure the source transit time The correction for transit time can be obtained from a linear regression analysis of integrated charges collected for different time intervals M is the slope of the resulting line The fractional contribution from source transit increases with source to chamber distance Figure 16 Therefore the linear regression analysis must be done for each distance If desired the source transit time can be obt
26. the manufacturers allow these sources to decay several weeks prior to shipment to allow the Ir to decay Some facilities have developed quality assurance dose rate check devices using diodes or ion chambers at fixed distances from the source Figure 9 A relative value of 100 activity is determined when the new source is installed and at each use or weekly the decayed source 60 activity is checked These devices check for source activity source position and timer accuracy We recommend this good practice procedure be done at sufficient frequency to ensure proper patient care considering the frequency of use of the afterloading unit Monthly or quarterly quality assurance checks generally include confirmation of timer accuracy and linearity confirmation of source positioning radiography of simulated dummy sources in conjunction with autoradiography of the active source Figure 6 checks of operation of the unit when power or compressed air is lost and checks of all emergency systems careful measurement of the lengths of source guide tubes and connectors to determine critical lengths have not changed and that all connectors function and a review of compliance with regulatory requirements proper signs posted and instructions present and proper daily or weekly QA logs completed per the license C Quality Assurance in the Use of Equipment As the use of remote afterloaders involves keying into a computer treatment parame
27. the sources the calibration of the sources the relative spatial position of the sources perturbing effects of adjacent sources and of the applicator and attenuation and multiple scattering in tissue surrounding the source and applicator all of which have previously been discussed The accuracy of computer dose calculations was addressed in an earlier section Generally the sources are 1 A single source which steps through a preselected positional sequence with different dwell times at each location 2 a single source that oscillates in a pre determined pattern to yield the desired dose location 3 the active source pellets that are interspaced with inactive pellets in a static linear array Some vendors provide precalculated isodose atlases that provide dose distributions for standard source arrangements and treatment times While these atlases are useful the user must clearly understand their assumptions so that corrections made and included in these dose distributions are not made a second time by the user Such atlases generally assign a reference activity for the sources and the user must 92 normalize the precalculated dose distributions to the activity or calibration of the source s used at the time of treatment unless such normalization is automatically performed by the machines Conventional radiotherapy planning RTP computer software often can be used to calculate the dose distributions of remote afterloader sources
28. units Certain pitfalls in such uses will be described and precautions will be suggested Methods for the design of facilities specifically for these systems will be outlined A review of currently available computation methods for dose calculations and optimization will be presented The specific charge to this task group is 1 To review the principles of operation of the commercially available remote afterloading systems 2 To recommend a procedure for the calibration of the strength of the sources employed in these systems 3 To suggest radiation control practices with special emphasis on emergency response procedures 4 To recommend quality assurance procedures for an efficacious use of these systems 5 To outline special considerations that must be addressed in the design of a facility for the use of remote afterloaders 6 To review the currently available methods for dose computation and optimization for treatment planning Ravinder Nath Chairman Radiation Therapy Committee December 20 1988 ii FOREWORD The most difficult task of Task Group 41 was to review methods of calibrations of high activity 370 GBq 10 0 Ci Ir sources used in high dose rate remote afterloading units and to recommend a calibration protocol for these sources While there have been significant developments in obtaining Ir calibration factors for thimble ionization chambers used for secondary standards relative to National Ins
29. warning lights in the room and over the door function properly during planned and unplanned room entry If other radiation producing equipment is in the room particular attention must be given to the location and proper functioning of entry way radiation status lights so that it is clear which unit is producing radiation 44 4 That the closed circuit television and intercommunication systems function properly 5 That the independent radiation monitor in the room performs properly using a radioactive check source and functions during treatments 6 That any other radiation producing equipment in the same room cannot be turned on simultaneously with the remote afterloading device 7 That the radiation exposure rates and conditions around the facility comply with those included in the license application 8 That emergency buttons in the room function properly 9 That installed compressed air lines maintain adequate pressure under load and for the planned duration of treatments 10 That any security system required for the storage of the remote afterloader when not in use functions properly C Source Transport Systems and Applicator Tests The testing includes but is not limited to confirming 1 The integrity of the source guide tubes that transport the source s to the applicator s For sources transported by cables source guide tube length is a critical parameter and source guide tube length gauges are used to confi
30. with conventional LDR brachytherapy is under active investigation Although this topic is beyond the scope of this report there are numerous literature articles to which the reader may refer However the advantages of remote afterloading therapy appear to outweigh the disadvantages and sales of remote afterloading units are increasing 22 Il FEATURES OF REMOTE AFTERLOADING SYSTEMS A Essential Features All remote afterloaders offer four essential features 1 A primary storage safe to contain the sources s when not in use 2 A mechanism to move the source s from the storage safe to and from applicator s in the patient 3 A system to maintain the source s in the applicator s for a set time in desired positions and to determine their position s 4 A mechanism to return the source s to the storage safe at the end of treatment and during power failures or other emergencies B Radioactive Sources The radioactive nuclides used in remote afterloading are Co Cs and Ir The first two offer longer half lives but lower specific activities than achieved with Ir Hence Co and Cs sources are used in LDR MDR or HDR devices designed for intracavitary treatment with applicators that have larger inner lumens that accommodate the larger diameter 3 to 4 mm Co and Cs sources Higher activity Ir sources with smaller diameters about l mm are best for intraluminal HDR treatments However the 73 8 d half life o
31. 1 L N Sedham and M I Yanni Radiation Therapy and Nurses Fears of Radiation Exposure Cancer Nursing 8 129 1985 C A F Joslin High Dose Rate Gynecological Afterloading in Institute of Physical Sciences in Medicine Report 45 Dosimetry and Clinical Uses of Afterloading Systems edited by A R Alderson Institute of Physical Sciences in Medicine London 1986 9 11 C A F Joslin High Activity Source Afterloading in Gynecologic Cancer and its Future Prospects Endocurietherapy Hyperthermia Oncology 5 69 81 1989 M Busch and W Alberti eds High Dose Rate Afterloading Therapy of Uterine Cancer Radiologisches Zentrum Universitatsklinikum Essen Essen FRG 1985 J F Utley C F Von Essen R A Horn J H Moeller High Dose Rate Afterloading Brachytherapy in Carcinoma of the Uterine Cervix Int J Radiat Oncol Biol Phys 10 2259 2263 1984 96 18 20 21 22 23 24 25 U Schulz M Busch U Bormann Interstitial High Dose Rate Brachytherapy Principles Practice and First Clinical Experiences with a New Remote Controlled Afterloading System Using Ir Int J Radiat Oncol Biol Phys 10 915 920 1984 Report to Congress on Abnormal Occurrences NUREG 0090 Vol 13 No 1 Jan Mar 1990 5 8 B R Thomadsen S Shahabi D A Buchler M P Mehta B R Paliwal Anatomy of Two High Dose Rate Misadministrations Med Phys 18 645 1991 Abstract W K Jones
32. AAPM REPORT NO 41 eae ie ees a ee eee REMOTE AFTERLOADING TECHNOLOGY AD e Published for the American Association of Physicists in Medicine by the American Institute of Physics AAPM REPORT NO 41 REMOTE AFTERLOADING TECHNOLOGY A REPORT OF AAPM TASK GROUP NO 41 REMOTE AFTERLOADING TECHNOLOGY Glenn P Glasgow Chairman J Daniel Bourland Perry W Grigsby Jerome A Meli Keith A Weaver May 1993 Published for the American Association of Physicists in Medicine by the American Institute of Physics DISCLAIMER This publication is based on sources and information believed to be reliable but the AAPM and the editors disclaim any warranty or liability based on or relating to the contents of this publication The AAPM does not endorse any products manufacturers or suppliers Nothing in this publication should be interpreted as implying such endorsement Further copies of this report 10 00 prepaid may be obtained from American Association of Physicists in Medicine 335 East 45th street New York NY 10017 International Standard Book Number I 56396 240 3 International Standard Serial Number 0271 7344 1993 by the American Association of Physicists in Medicine All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording or otherwise without the prior written permission o
33. ECHNIK TECHNIK TECHNIK Engineering Dr Sauerwein Dr Sauerwen Dr Sauerwein Manufacturer BV GmbH amp Co GmbH amp Co GmbH amp Co or Vendor T Pse Rates 2 Modality Germany ntracavitary Intraluminal Interstitial Interstitial Intraluminal intrasuminal a fa 12 Uses Conventional fYes or uses dedicated Yes Busch Isodose Yes also has Yes also has RTP Software for IBM PC and software Atlas IBM PC compatible IBM PC compatable IBM PC Desimein 3 Dose Yes 300 optimization Yes 60 opumization Yes 60 aptimizaton Yes 60 optimization Optimization Jpoints ponts points points Available gt 14 Bladdes and Can terminate treat Can terminate treat Can terminate treat Rectal ment at preset doses jment at preset doses ment at preset doses Dosimetry i 1S Source Container Co 10 Ci Ir 20 Ci Ir 20 Ci Ip 20 Ci Maximum Storage Activity 16 Special Features Pneumatic checks of Storage of jMemorize storage of source positions 23 treatments jail planned and treated patients 1 Number of Applicator Channels 24 18 Maximum Number 20 of Sources in Projector 19 Maximum Number 3 of Channels Used Simultaneously 20 SOURCES a Radmsntope ir mip m Physical Size r 1 8 mm x 8 mm 11 mm x amp 5 mm 1 1 mm x 8 5 mm lor x 65 mm or x 6 5 mm 10 Ci 10 Ci 16 The original low dose rate Selectron was designed for up to forty eight spheric
34. TECHNIK Dr Saverwein Dr Saserwen Dr Sauerwein GmbH amp Ce GmbH amp Co GmbH amp Ce Germany Germany Germany Intracavitary ntracavitary ntracavitary intraluminal Interstitial Interstitial Intraluminal Intralaminat 3mm to 8mm 1 6mm to amp mm 1 6 mm to 8 mm Source electron beam Source electron beam Source electron beam welded to steel drive welded to steel drive welded to steel drive cable cable cable Stepping motor 20 steps to 2d mm length Stepping motor 20 steps 200 mm max also lmm steps Stepping motor 40 steps to 400 mm length 1 mm to 10 mm steps Hand crank Hand crank backup battery backup battery 1 104 Dummy Source Fletcher Manchester Fletcher Manchester Fletcher Manchester vaginal shielded vaginal shiekded vaginal shielded rectal shielded rectal shielded rectal shielded numerous intraluminal applicators applicators catheters rigid flexible needtes rigid Mexible templates needles templates I mm l mm timm Stepping source in O S em or 1 0 em steps 20 steps 20 cm length covered Stepping sources and dwell times to 999 sec in 0 1 sec increments Stepping source and dwell times to 999 sec in 0 1 sec increments 15 Table 2 b Cont d High Dose Rate Remote Afterloading Devices Selectron Gamma Med II Gamma Med Ili Gamma Med 12i HDR ISOTOPEN ISOTOPEN TSOTOPEN Nucletroa T
35. able for use with LDR and HDR units However AAPM Radiation Therapy Committee Task Group 40 has recommended that 57 for a single source the computed isodose curves have a tolerance to within 2 along the radial dimension of linear sources and a 5 tolerance for isodose curves near the end of the sources Jayaraman and Lanzl noted however that corrections for source capsule effects in linear low dose rate sources have uncertainties of about 2 Moreover tissue attenuation and multiple scattering corrections at l cm radially from a line source vary from 2 to 4 depending on the isotope These authors conclude that the overall uncertainty in the dosimetry at regions of clinical interest will be limited to about 6 depending on the radioisotope and source model Consistency is more important than absolute accuracy Each user must establish an initial baseline source dosimetry single source isodose distributions in air in tissue and in applicators should be compared to those generated by other users using the identical source model Details of the parameters used to establish these baseline single source dose distributions should be fully documented Any changes in these parameters or in the computer models used to generate these baseline dose curves must also be noted We stress again the importance of the user fully understanding the computation algorithms and the parameters used VII QUALITY ASSURANCE Quality assuranc
36. ained from the linear regression analysis on M obtained from Eq 11 Alternately the charge collection rate M can be taken as equal to the difference between the charge collected for two timed measurements divided by the difference between the corresponding times The subtraction of the two integrated charges removes the contribution from source transit because it is independent of time In this case M z M t M C s 18 3 Selecting a Source Strength Does the measurement of apparent activity exposure rate or air kerma rate at a stated distance or other derived parameter agree with that stated on the source calibration certificate AAPM Task Group 40 recommends that if the verification measurements disagree with the manufacturer s value by more than 3 the disagreement should be investigated discrepancies greater than 5 should be reported to the manufacturer It further recommends that clinical calculations be based on the local measurement of the source strength and that discrepancies relative to the manufacturer s value serve to motivate a thorough check of the calibration procedures followed and if indicated a repeat measurement 84 30 42 4 H O Lu LL U Lu Q Z ui X10 HOURS e 10 0 3 DISTANCE cm Figure 16 End effects timer error versus distance for a Selectron LDR unit Each unit will have a different timer error Courtesy of G P Glasgow Maywood IL 85 Disagreem
37. al Cs sources with activities from 370 MBq 0 01 Ci to 1 48 GBq 0 04 Ci and included three channels for moving the sources into various gynecologic applicators The current Selectron transfers pellets pneumatically and a microprocessor controls source pellet arrangements The current device is available with either three or six channels the latter allows treatment of two patients simultaneously The MicroSelectron LDR a low dose rate interstitial unit features fifteen channels used with a secondary storage safe that can accommodate up to 45 different source configurations The unit can use either conventional Ir seeds in ribbons or Cs seeds in a preselected configuration The secondary storage safe allows the user to purchase and use a large number of sources designed for use in specific sites 137 The Omnitron Model 2000 features a high dose rate 370 GBq 10 0 Ci Ir source only 0 59 mm in outside diameter it can be used with 20 gauge needles of 0 89 mm outer diameter or in a smaller catheter of l l mm outer diameter The source has a total extension distance of 150 cm and steps in 1 l cm increments The OmniCath a special catheter features a releasable stainless steel marker that can be sutured in place Sealed access posts on the distal end of the catheter allow fractional HDR treatments for as long as three weeks When the catheter is removed the proximal stainless steel marker is released and remains at the implant si
38. apy in Gynecology International Commission on Radiation Units and Measurements Bethesda MD 1985 5 G P Glasgow An Inventory of Cesium 137 Seeds for Multiple Site Interstitial Brachytherapy with a MicroSelectron Endocurietherapy Hyperthermia Oncology 5 175 179 1989 D J Brenner and E J Hall Conditions For The Equivalent of Continuous To Pulsed Low Dose Rate Brachytherapy Int J Radiat Oncol Biol Phys 20 181 190 1991 K R Das A Shanta N Kulkarnic P K Shah Ralston 20B A High Dose Rate Remote Controlled Afterloader for Brachytherapy Endocurietherapy Hyperthermia Oncology 3 81 89 1987 K C Kam and P Dunn First Year Experience with the High Dose Rate Buchler Afterloading Unit in Institute of Physical Science in Medicine Report 45 Dosimetry and Clinical Uses of Afterloading System edited by A R Alderson Institute of Physical Sciences in Medicine London 1986 46 59 C H Jones and A M Bidmead Calibration of the MicroSelectron HDR System in Brachytherapy 2 Proceedings of the Sth International Selectron Users Meeting edited by R Mould Nucletron International BV Leersum The Netherlands 1989 75 82 C F Mesina G A Ezzell J M Campbell C G Orton Acceptance Testing of the Selectron High Dose Rate Remote Afterloading Cobalt 60 Unit Endocurietherapy Hyperthermia Oncology 4 253 256 1988 99 41 42 43 44 45 46 47 48 A Buffa Gamma Med
39. ard methods of treating specific anatomic sites should be adopted so that standard key entry procedures are followed Misadministrations most likely will occur when a treatment plan requires use of non standard parameters and someone keys in the usual standard parameters We encourage users of remote afterloading units to share in their user groups written materials which have been prepared for the use of specific units Equipment quality assurance and equipment use quality assurance are both dynamic processes procedures once established should be reviewed at least annually to determine if the entire QA program is effective and efficient and if not changes should be made to improve the program The QA program must be well documented for license compliance VIII SOURCE CALIBRATIONS A Source Certificates Purchased radioactive sources are provided with a certificate that describes the source and its activity apparent activity or other quantity related to activity e g equivalent mass of radium with a specific wall filtration Preferably the certificate should state the exposure rate or reference air kerma rate in uGy h in free space at a given distance in a specified geometry or the air kerma strength in pGyem h Whatever concept or term used to describe the source the user needs to confirm the stated certificate value to within its stated uncertainty Often the uncertainty in the absolute accuracy of source certificat
40. artinez C G Orton R F Mould Nucletron Corp Columbia MD 1990 138 159 E D Slessinger Selectron LDR Quality Assurance Selectron Brachytherapy Journal 4 36 40 1990 C H Jones Quality Assurance in Brachytherapy Med Phys World 6 4 1990 101 58 59 60 6l 62 63 64 65 F Cerra and J F Rodgers Dose Distribution Anisotropy of the Gamma Med II Brachytherapy Source Endocurietherapy Hyperthermia Oncology 6 71 80 1990 C C Ling Z C Gromadzky S N Rustgi J H Cundiff Directional Dependence of Radiation Fluence from 192 Ir and 198 Au Sources Radiology 147 791 792 1983 C Thomason T R Mackie M J Lindstrom P D Higgins The Dose Distribution Surrounding Ir 192 and Cs 137 Seed Sources Phys Med Biol 36 475 493 1991 R A Siwek P F O Brien P M K Leung Shielding Effects of Selectron Applicators and Pellets on Isodose Distributions Radiotherapy and Oncol 20 132 138 1991 American Association of Physicists in Medicine AAPM Report No 21 Specification of Brachytherapy Source Strength American Institute of Physics New York 1987 S Jayaraman and L H Lanzl An Overview of Errors in Line Source Dosimetry for Gamma ray Brachytherapy Med Phys 10 871 875 1983 American Association of Physicists in Medicine Report No 13 Physical Aspects of Quality Assurance in Radiation Therapy G K Svenson Chairman American In
41. at a minimum 1 Describes the functioning of the control console options 2 Provides instructions on how to retract sources and verify that they are retracted prior to entering the room 3 Describes emergency procedures including instruction on how to handle a dislodged source 4 Provides a list of names and telephone numbers of people to contact in case of an emergency 5 Describes the physical features of the sources used 6 Describes the functioning of the independent radiation monitoring system 7 Specifies the radiation warning signs to be posted 38 E Source Exchange Procedures The frequency of source s change is at the discretion of the institution Although detailed instructions to accomplish these changes should be part of the Physicist Engineer Manual source changes must be done only by qualified and properly trained personnel as defined in the license application Upon receipt of new sources appropriate radiation safety procedures must be followed Ideally the transfer of sources from the safe to the shipment container and vice versa should be done remotely from the control console outside the room or from a properly shielded area in the room Policies and procedures for handling radioactive sources of remote afterloaders are in general conceptually the same as for conventional brachytherapy sources but obviously vary depending on the amount of radioactivity in the sources and the frequency with whic
42. atheters using a guide wire after catheter placement but before the catheter is used with the radioactive source the open end is closed by inserting a small metal sphere into the tapered end of the catheter We emphasize that separate written procedures must be established for each category of emergency These procedures must stress alternate actions to take if the first emergency response fails The procedures must not only be posted but practiced by those responsible for operating the units and treating the patients G Training Courses As part of the purchase price the vendor should include a training course to be attended by those who use and operate the equipment usually physicists engineers if applicable dosimetrists technologists and or chief technologist and health physicists and attending physicians if they are operators The course should thoroughly review 1 Available applicators and their proper use 2 The functioning and operation of the unit under normal conditions 3 The function and operation of the unit under emergency conditions 4 All safety features 5 Radiation protection procedures 6 Suggested quality assurance procedures 41 7 AU aspects of the dose calculation treatment planning system if applicable The physicist and engineer should also receive detailed instruction on source exchange procedures They cannot be considered qualified to exchange sources until they have met whate
43. ation Chamber Dosimetry Procedure For Brachy Beam Dosimetry and Displacement Effects in Photon Beams Thesis University of Gothenburg Sweden 1991 F H Attix Introduction To Radiological Physics and Radiation Dosimetry John Wiley amp Sons New York 1986 346 394 L L Meisberger R J Keller R J Shalek Effective Attenuation in Water of the Gamma Rays of Gold 198 Iridium 192 Cesium 137 Radium 226 and Cobalt 60 Radiology 93 953 957 1968 H J Van Kleffens and W M Star Application of Stereo X Ray Photogrammetry SRM in the Determination of Absorbed Dose Values during Intracavitary Radiation Therapy Int J Radiat Oncol Biol Phys 5 559 1979 105 91 92 93 94 95 96 97 98 99 C Thomason and P Higgins Radial Dose Distribution of Ir and Cs Seed Sources Med Phys 16 254 257 1989 J A Meli A S Meigonni R Nath Comments on Radial Dose Distribution of Ir 192 and Cs 137 Seed Sources Med Phys 16 824 1989 K A Weaver V Smith D Huang C Barnett M C Schell C Ling Dose Parameters of I 125 and Ir 192 Seed Sources Med Phys 16 636 643 1989 V Krishnaswamy Dose Distribution about Cs Sources in Tissue Radiology 105 181 1972 B L Diffey and S C Klevenhagen An Experimental and Calculated Dose Distribution in Water around CDC K type Cesium 137 Sources Phys Med Biol 20 446 1975 C Thomason T R Mackie M J Linds
44. ational Selectron Users Meeting Nucletron International BV Leersum The Netherlands 1989 4 Proceedings of the First Symposium on Gamma Med Remote Afterloading Mick Radio Nuclear Instruments Inc New York 1985 5 S M Shah ed Proceedings of the First International Meeting of Gamma Med Users Mick Radio Nuclear Instruments Inc New York 1986 6 Proceedings of the Second Annual International High Dose Rate Remote Afterloading Symposium Robert F O Conner South China ME 1987 7 A A Martinez C G Orton R F Mould eds Brachytherapy HDR and LDR Proceedings of Remote Afterloading State of the Art Conference Nucletron Corporation Columbia MD 1990 8 P N K Leung Experience with Remote Afterloading Technique in Intracavity Therapy Int J Radiat Oncol Biol Phys 10 157 162 1984 95 11 16 P W Grigsby C A Perez J Eichling et al Reduction in Radiation Exposure To Nursing Personnel With the Use of Remote Afterloading Brachytherapy Devices Int J Radiat Oncol Biol Phys 20 627 629 1991 United States Nuclear Regulatory Commission Code of Federal Regulations Title 10 Chapter 1 Part 35 20 October 31 1986 C Constantinou Investigations and Reporting of Incidents and Accidents in Radiotherapy in American Association of Physicists in Medicine Proceeding No 4 Radiotherapy Safety edited by B Thomadsen American Institute of Physics New York 1982 23 3
45. attery system that will prevent loss of computer data during power failure ideally it will also allow a power interrupted treatment to continue 2 An interrupt button to allow treatment to resume after a planned interruption 33 3 A simulation mode using dummy sources to test source guide tubes and applicator clearances immediately prior to treatment 4 Clear console indicators that show when the source is in and out of the safe and when the door is closed and opened 5 A last resort mechanical system for manually returning the source to the safe in the event other electrical source return mechanisms fail B Radiation Surveys After installation of the remote afterloading unit and sources in the treatment facility a radiation survey must be performed under the conditions assumed in the license application to confirm that the instantaneous exposure rates around the unit do not produce dose equivalents in excess of those projected in the license application For the routine use of LDR and MDR units it may not be necessary to measure the exposure rate outside the patient s room and in adjacent rooms for each patient if the license application established alternate procedures to prove that exposure rates in unrestricted areas comply with regulatory standards this is preferable to doing surveys for each patient C Routine Precautions Routine radiation control procedures include but are not l
46. avitary ntracavitary ntraluminal Interstitial Interstitiat Intracavitary Uses Conventonal Yes has IBM PC and Yes using point source Yes using point source Yes or uses dedicated programs isodose atlas program isodoce atlas IBM PC Yes 40 optimization points No ir 10 Ci Memory storage of iprior treatments imultipte fractions 18 Ir ca peute S mm L x Limm OD 10 Ci eS C 5 O Se 2 a ey 14 Table 2 b High Dose Rate Remote Aftertoacing Devices 10 u Outside Diameter of Applicators Method of Source Transfer Method of Source Movement Method of Source Retraction in the Event of Failure Storage of Source Simulation Sources for Treatment Simulation Applicators Available Accuracy of Source Position Source Arrangements and Dose Calculations Selectroa HDR Nocletron Engineering BY Netherlands niracavitary Intraluminal Intracavitary Co 6 mm Pneumatic microprocessor controlled Source trains with 48 pellets over 120 mm any pellet may be programmed to be active inactive Emergency battery to operate reservoir for y penumatic retum or j gravity AIl in unit 10 Ci max Dummy Source gt 60 available 1 mm with Pneumatic check Point sources l individually constructed to yield any desired distribution Gamma Med If Gamma Med Ili Gamma Med 12i ISOTOPEN ISOTOPEN ISOTOPEN TECHNIK TECHNIK
47. by small radioactive sources inserted into small lumens esophagus bronchus bile duct etc while intracavitary and interstitial retain their historical meaning Intraoperative denotes irradiation during surgical operations 3 Outside Diameters of Intracavitary Intraluminal and Interstitial Applicators Self explanatory but important as the applicators outside diameters are the limiting factor for treating certain anatomic sites 4 Method of Source Transfer to the patient from projector or device Methods include ball chains drive cables helical steel springs and pneumatic techniques 5 Method of Movement Methods include oscillating cams stepping drive motors and use of active inactive pellets to achieve desired source configurations and dose distributions 6 Source Retraction in Event of Failure If power fails how will sources be removed from the patient Falling weights back up batteries and hand cranks all are used 7 Source Storage Where are sources stored Is there any additional storage device other than the treatment unit Does the unit have a second or supplemental storage unit 8 Simulation Sources for Treatment Simulation Are inactive sources available that allow simulation of the planned therapy 9 Applicators Available Self explanatory and dependent on source design 10 Accuracy of Source Positioning How accurately will the unit position an individual source or source array in a patient T
48. careful reviews by Lowell Anderson and by Radiation Therapy Committee members D W O Rodgers Azam Niroomand Rad and J R Palta of draft reports We appreciate the valuable work of Ms Gina Tejcek Loyola University of Chicago in typing the many drafts of this report ABSTRACT Remote afterloading of low dose rate LDR medium dose rate MDR and high dose rate HDR radioactive materials for brachytherapy is increasingly practiced in the United States This report presents the advantages and disadvantages of the units lists some commercial remote afterloaders and their features and reviews facility requirements radiological safety licensing and license compliance calibration methods acceptance testing quality assurance and isodose computation TABLE OF CONTENTS PAGE I Tntroductioti sssr annann aaa aa s a rA EEA Aae ed sas 1 A Advantages of Remote Afterloading E ESCE EEEIEE EEES 1 B Disadvantages of Remote Afterloading KEREKEKRE AKEKE 3 II Features of Remote Afterloading Systems 4 A Ess ntial Features E an anora A nou nouns 4 B Radioactive Sources 4 C Compendium Contents 5 D Remote Afterloading Devices 8 Ill Patient Populations Equipment Selection Facility Design 19 A Patient Populations and Equipment Selection 00 19 B Facility Design Low Dose Rate sss 20 C Facility Design High Dose Rate 26 Dis COSTS iraro E Er A 30 IV Licenses and License
49. catter Courtesy of Miles Mount Nucletron Corporation Columbia MD 72 Figure 13 b Calibration stand designed to minimize radiation scatter Courtesy of Felix Mick Mick Radio Nuclear Inc New York NY 73 error corrections which represent the charge collected during source transit and smaller room scatter contributions as a percentage of the measured charge However exposure gradient corrections necessary for the finite dimensions of the chamber volume are larger small positional errors cause greater percentage errors in the measured charge Conversely at larger distances where integrated charges are markedly less source end effects timer errors are larger and room scatter contribution represents a larger percentage of the measured charge However the exposure gradient corrections are much smaller and positional errors are less important Leakage charge corrections may be larger The in air calibrations can be done by using integrated charge measured at a single distance or at multiple distances as described in d which follows In addition to the conventional electrometer chamber charge collection efficiency corrections the single distance charge measurements may require corrections for a air attenuation and multiple scattering b the exposure gradient across the chamber c the room scatter effects e and end effect timer errors a In air attenuation and multiple scattering of photons fi
50. cm Both University of Wisconsin ADCL and K amp S Associates Inc ADCL use this interpolative method to obtain N for chambers Ezzell reports a 1 2 increase in his previously reported calibration factor using Goetsch et al technique relative to the calibration factor obtained by Ezzell s method of interpolation between a chamber factor for Co with a cap and 250 kV without a build up cap This interpolative method likely will serve as the best method of obtaining an Ir calibration point until NIST develops a direct method of chamber calibration with Ir Users of HDR Ir sources who desire to calibrate their sources by 70 thimble ionization chamber measurements may request a 250 kV calibration point and a Cs calibration with the same cap the wall plus cap thickness can be greater than 0 31g cm graphite but should not be less Since the AAPM Task Group 3 has approved this interpolative method of obtaining NJ we suggest users follow the identical procedure as described by Goetsch et al 2 In Air Calibrations In air calibrations should be done at large distances relative to the dimensions of the radioactive source s preferably with a spherical ionization chamber If a cylindrical chamber is used the long dimension of the collecting volume should be perpendicular to the longest dimension of the source s Source holder ion chamber holder and support stand should be low density plastic to
51. concrete Cae ighting Q Temote afterloader storage position camera monitor remote afterloader control console audio camera 2 monitor TerOke radiation indicator 2 p camera remote afterloader veatment positon xray control console anesthesia z Temote Se Je p panent B 3 momtoring opuonal treatment planning workstation FP denotes emergency off button scale 1 3 inch 1 0 foot amp denotes emergency power Figure 4 A dedicated HDR remote afterloading treatment suite with ancillary equipment Modified from Ref 45 courtesy of J D Bourland Rochester MN 28 26 25 by 6 4 m 21 with 46 cm 18 concrete walls well equipped as a minor procedure suite Radiological safety requirements for a dedicated HDR vault are essentially those required for a cobalt teletherapy vault These include positive action door interlocks that retract the source when the door is opened and an emergency button that when pushed will retract the source Both of these will not allow the source s to leave the shielded device until the proper reset sequence is completed Other features include warning lights visible and audible alarms remote closed circuit video camera CCTV and intercommunication devices for monitoring patients radiation detector independent of the HDR visible access alarms above the maze door and a cable pass for dosimetry cables A vault equipped for minor
52. constant contributor at all measurement distances i e independent of the source to chamber distance then X X d d X R 6 where a ll distance from the source to the point of measurement A Il o distance from the source to a reference point X total exposure primary plus room scatter at d X primary exposure at d X room scatter exposure assumed constant for all d By making measurements of equal duration at distances of 20 30 40 and 50 cm regression analysis of X versus d d will yield X and X The measurements must be corrected for other distance dependent factors such as end effects timer error and chamber gradient corrections prior to the analysis As the room scatter is likely less than 0 5 very careful charge measurements are required with proper measurements of leakage charge Goetsch et al expanded the method of Ezzell They used an independent timer to trigger a pulse to an electrometer to start and stop charge integration while the source remained at the desired source to chamber location In this way they eliminated the need to 79 make corrections for the source transit time For in air measurements the chamber response was corrected to account not only for room scattered radiation but also for the effective distance between source and chamber centers These corrections were handled by considering deviations from the inverse square law which applied only to primary photo
53. d not shown covers and is suspended from the ceiling above Note the compressed air supply dedicated electric outlet radiation monitor remote control and telephone power assisted door opener 1 2 lead wall shields and supplemental lights over head 21 ADJACENT ROOM HALLWAY REMOTE CONTROL amp TELEPHONE RADIATION MONITOR D sHiecos ZZZ S ADJACENT ROOM Figure 2 A two room treatment facility for gynecologic treatments using single remote afterloading unit RAU The hallway and adjacent patient rooms are shielded using portable bed shields Courtesy of P W Grigsby St Louis MO 22 unit and bed shield are present sometimes nurses move bed shields to facilitate patient care and fail to reset them in required shielding positions The weight of bed patient bed shield and LDR unit are all concentrated in a small area and can approach the structural live load limit of the floor the floor structural load limit must be carefully reviewed when adding heavy radiation shielding and equipment to any existing structure While shielded walls generally are more expensive than bedside shields they offer the practical advantage of always being intact and allow more useable space in the room A closet adjacent to the room or in the room Figure 1 can be used for storage of the LDR unit when not in use this allows the room to be used by patients not receiving brachytherapy Ancillary support equipm
54. devecteecerssasedss 62 B Well Ionization Chamber Calibration of Low and High Activity SOUTCES AerK EO EEO OVE EG 63 C Use and Quality Assurance of Well Ionization Chambers 65 D Ionization Chamber Calibration of LDR amp HDR Sources 68 1 Chamber calibration factors 69 2 Ta Air Calbia onsi ssn sss a RE 71 a Air attenuation and multiple scattering 74 b Dose gradient correction cece 74 ROOM SCAtErs t sicscies tiniest ssi esis EE aR 77 d Calibration equation cscs 81 e End effects timer error s s ss ssssssesseersessresseersesseess 83 3 Selecting a source Strength 84 4 Dose to the medium from in air calibrations 87 5 Calibrations in water for solid phantoms e 91 TX Tsodose Computations ccccccssssscsssssssssssesssssesscesseccessseceessnsessnseeesees 92 References 95 vi I INTRODUCTION Remote afterloading of radioactive materials for brachytherapy is increasingly practiced in the United States The earliest remote afterloading devices developed in the early 1960 s were refined and used for brachytherapy in England Europe and at a few facilities in the United States Originally there were only a few manufacturers of these devices Several current manufacturers offer devices with many diverse features A review of proceedings of the meetings sponsored by the device manufacturers reveals that radiation oncologists are using remote afterloading
55. e s activity will be between 5 to 10 62 Additionally the certificate should state if the mean activity and its uncertainty were determined by measurements of a small number of radioactive sources selected from a larger batch a common method of assaying low activity seeds or measurements of the activity of each source received by the user AAPM Report 21 describes levels of traceability of brachytherapy source calibrations relative to MST and ADCL laboratories Direct or secondary traceability is desired B Well Ionization Chamber Calibrations of Low and High Activity Sources The sources to be calibrated in remote afterloading devices are characterized as either short or long lived radionuclides of low or high activity Three types of re entrant well ionization chambers exist Conventional chambers designed for measuring the activities of quantities of radiopharmaceuticals used in nuclear medicine brachytherapy chambers designed to measure the activities of Cs tubes and needles Ir seeds and other low activity sources and chambers designed to measure the activities of HDR sources Nuclear medicine chambers are designed to assay liquid radiopharma ceuticals contained in syringes or glass vials Calibration factors for specific radionuclides are obtained by measuring the activities of certified activities of radionuclides in 5 ml glass ampules of standard design Generally these calibration factors do not apply if
56. e procedures must be established for the equipment e g the remote afterloader unit and its ancillary accessories and for the process of using the equipment e g proper execution of a planned treatment A Equipment Quality assurance tests are designed to confirm that the system remote afterloading unit facility applicators sources etc performs within the tolerances established during the acceptance tests In some cases the quality assurance test procedure is identical to the acceptance test procedure in other cases less rigorous quality assurance tests are performed 58 AAPM Report 13 Physical Aspects of Quality Assurance in Radiation Therapy recommends quality assurance procedures for both conventional and remote afterloaders in brachytherapy AAPM Task Group 40 has a draft document 1992 on comprehensive quality assurance procedures that includes a chapter on quality assurance for conventional manual brachytherapy and remote afterloaders Generally the quality assurance procedures recommended for conventional low dose rate brachytherapy sources sealed tubes seeds apply whether these sources are handled remotely or manually However additional quality assurance procedures are required for the remote afterloading unit Moreover the exact types of acceptance tests and quality assurance procedures will depend on the type of the remote afterloader system and the type of radioactive sources We encourage readers of this r
57. ed HDR room and ancillary x ray imaging equipment will likely cost 200 000 to 500 000 Locating an HDR device in a shielded radiotherapy vault with external beam equipment used daily eliminates the cost of building a dedicated room or renovating an existing room but limits the availabiity of the HDR device and teletherapy unit and complicates patient scheduling Moreover the radiotherapy vault may not accommodate desired x ray imaging equipment required for source localization Patient misadministrations still can occur because of operator error in programming or entering incorrect treatment parameters Radiation emergencies still occur Source guide tubes can detach from the machines or patients LDR and HDR sources can become lodged in the source guide tubes Unshielded HDR sources offer potentially higher inadvertent radiation exposure to personnel than unshielded LDR sources Extensive routine and emergency radiation control procedures must be developed to ensure proper use and control of LDR MDR and HDR sources Finally relative to conventional manual LDR methods for either LDR or HDR remote afterloading brachytherapy the historical data bases of five year survival rates and early and late tissue complication rates by anatomic site are not as extensive Numerous treatment regimens and fractionation schema are used in HDR brachytherapy The number of fractions and doses to provide treatment results equivalent to those obtained
58. eisberger R J Keller R J Shalek Radiology 93 953 957 1968 H J Van Kleffens and M W Star Int J Radiat Oncol Biol Phys 5 559 1979 As previously discussed Figure 10 the encapsulation of sources generally produces a dose anisotropy with reduced dose rates toward the ends of the source relative to dose rates at the same distance on the perpendicular bisector For Co and Cs sources few recent reports of F r 0 exist Krishnaswamy documented the dose anisotropy of Cs tubes relative to Ra tubes and Diffey and Klevenhagen also reported the dose anisotropy of Cs tubes used for manual afterloadiig Thomason et al investigated dose distributions surrounding Ir and Cs seeds and the effects of source encapsulation 89 Table 7 Polynomial fitting coefficients for models in Table 6 Van Kleffens Meisberger et al Coefficients amp Star Coefficients Isotope A B C D a b Ci x 105 k0 amp 10 x10 10 Au 1 0306 8 134 1 111 15 970 Tp 1 0128 5 019 1 178 2 008 oo Gs 1 0091 9 015 0 3459 2 817 83 10 8 Ra 1 0005 4 423 1 707 7 448 68 9 7 Co 0 99423 5 318 2 610 13 270 10 0 14 5 a PT AE ENEE AEE SE E E EEEE L L Meisberger R J Keller R J Shalek Radiology 93 953 957 1968 H J Van Kleffen and M W Star Int J Radiat Oncol Biol Phys 5 559 1979 For sources specifically designed for LDR and HDR remote afterloaders values of
59. ell if they remain there for several minutes Styrofoam thermal absorbers can be positioned around the source holder to alleviate this problem Collection efficiency is a function of current which is proportional to the HDR source activity As the source activity decreases the collection efficiency may increase slightly As with external beam chambers it may be necessary to measure this phenomenon by measuring current produced at multiple voltages As the well chambers connect to the electrometers via cables care should be paid to leakage currents and other cable related phenomena that can affect charge or current readings Finally it is important to test at frequent intervals using a long lived radionuclide Cs Sr the constancy of the well chamber response This may be difficult for an HDR chamber as long lived high activity check sources are not readily available Consider using the highest activity Cs or Co sealed source one can obtain alternately place the well chamber in the beam of a Co teletherapy unit and measure the current collected in a standard reproducible geometry A reproducibility of at least 0 5 is desired Well ionization chambers will respond to scatter radiation Hence when used they should be placed well away from walls that may scatter radiation back to the chamber They should be used in the same location in a constant geometry in a reproducible manner If moved from one location to anot
60. ent such as an air compressor used with pneumatic units can be housed here to reduce noise in the treatment room Ceiling and floor shielding may be required for adequate protection of patients or personnel a projection shield placed in or beneath the bed is a practical alternate to shielding the floors for some rooms The best entry way to the room features a small maze Figure 3 with the operator s control inside the protected maze Usually this design will eliminate any shielding in the door and keep all operating controls secure inside the room Unfortunately many existing hospital rooms are too small to allow even a small maze Depending on the bed location relative to the door power assisted shielded doors Figure 1 may be required as in radiation therapy vaults Door interlocks that retract the sources when the door opens are usually required Operating mechanisms placed outside the room in an adjacent hallway Figure 1 are less secure from unauthorized use than those located inside the room in a mare but location on a hallway wall adjacent to the door is common Patient room lights are often inadequate Supplemental lights over the bed will make it easier to see source guide tubes and check applicators protruding from the patient An independent radiation monitor in the room generally is required As it will be on when the patient is treated some forethought should be 23 Dedicated Low Dose Rate Remote Afterloading Room
61. ent between numbers often is expressed by the ratio of the measured to manufacturer value However caution is advised as the uncertainty in each value must be considered For example Ir seed activities commonly are expressed with standard deviations as large as 7 Similarly a batch of Cs pellets in an LDR remote afterloader has activities matched to within 5 Figure 17 Experimental measurements made of only a sample of sources from a batch must be evaluated considering the stated spread of source activities in the batch Relative Activity Per Source m Manufacturer g Measured Number 0 965 0 985 1 Figure 17 Relative activities of 18 Cs pellets in a Selectron LDR Measurements in a well ionization chamber confirmed the manufacturer s stated relative activities were within 5 of the mean activity of the 18 pellets Courtesy of G P Glasgow Maywood IL 86 Unfortunately the single Ir high activity 370 GBq 10 0 Ci sources now available usually have a source activity or related parameter stated to only 10 accuracy A consistent and reproducible method of verification measurements is vital and the uncertainty and reproducibility of the verification measurements should be known and considered when deciding if the verification measurement agrees or disagrees with the manufacturer s stated value Reproducibility of in air measurements can be established conveniently by measuring both the old and new so
62. eport to concurrently read the report that will result from the work of Task Group 40 Two extrinsic factors affecting the quality assurance program include the location of the remote afterloader and the workload and frequency of use of the unit If remote afterloading units are in dedicated treatment rooms or vaults unused by other patients equipment quality assurance is easier to perform as it generally can be done during regular work hours If the unit is in a teletherapy vault access for quality assurance may be limited to after hours Moreover if a LDR unit is in a room used by non therapy patients access may be very difficult as it requires blocking the room for periods of times so that it is not used by patients B Frequency and Type Of Equipment Quality Assurance Tests There are no legal standards established for the frequency with which quality assurance tests should be performed other than those written in a license application Equipment quality assurance checks should be performed at sufficient frequency to guarantee that the equipment works properly during a therapy session 59 The frequency of quality assurance testing often is determined by the frequency of use of the equipment Generally a unit used daily should have functional tests performed daily or weekly Verify that the console keys and lamps work that tape or computer printer works and has adequate paper for the duration of the treatment that the closed
63. er of lead supported and centered on the central axis by a flange of cork so that when the source probe is placed in a re entrant axial hole in the lead the current created in the chamber is sufficiently reduced This method has been used at Memorial Sloan Kettering Cancer Center for several years to measure the strength of new and old sources at source exchange and to monitor reproducibility by the ratio of the new source strength to the old source strength corrected for radioactive decay C Use and Quality Assurance of Well Ionization Chambers Well chambers generally exhibit a strong energy dependency any well ionization chamber needs to be calibrated for the radioisotope for which the calibration certificate value is to be measured Nuclear medicine well ionization chambers are not likely to be calibrated for Ir average energy of about 0 38 MeV poly energetic spectrum but will likely have a Au calibration factor 0 412 MeV monoenergetic While the average energies are similar a RADCAL Model 4050 ionization chamber has relative to Ra about 10 higher response for the Ir than for Au Figure 11 and the Au calibration factor should not be used for Ir Source encapsulation and capsule design affect calibration A calibration for a radioisotope is specific to the wall thickness of that capsule the well chamber will respond differently to the same radioisotope in a different source encapsulation Changing the thickness
64. erstitial needles bronchial 14 guage esophagus intra cavitary of many types l mm Not stated in l mm I mm commercial literature Stepping source Pre loaded sources Shifting mechanisms Point source at and variable arranged to give move sources to 48 pocitions 25 mm dwell times desired distribution selected positions apart dwell times to Conventional 999 seconds in 0 1 g second increments 13 Table 2 a Cont d High Dose Rate Remote Afterloading Devices Afterioading BUCHLER Facts Curietren Manufacturer Bucher GmbH amp Co Oris CIS US or Vendor Germany France Dose Kates 3 Modality ntracavitary Totraluminal Interstitial 12 3 LGI 15 16 17 18 19 RTP Software forjsoftware Dosimetry Dose Optimization Available Yes No Bladder and Rectal Dosimetry Yes Option Source Container Ir 10 Ci TCs Ci HDR Maximum Storage Activity Speciat Features Memory storage of Checks and confirms all planned and microprocessor treated patients Number of 12 4 Applicator Channels Maximum Number 10 or 20 of Sources in Projector Maximum Number 1 4 of Channels Used Simultaneously SOURCES AVAILABLE a Radioisotope Ir Cs Physical Size 4 1 mm L Capsules in train x L mm OD 20 3mm 10 Ci x 2 65 mm OD 75 mm L x 11 D S00 or Yes Yes ir 2x 10 Ci Checks and confirms microprocessor 20 Ir Capsute 1 2 mm OD x 14 mm 12 Ci Hig ntrac
65. f Tr necessitates three to four source changes yearly at an annual cost of 8 000 to 15 000 C Compendium Contents Tables I and II compare features of commercially available remote afterloaders These data represent the authors understanding of features of each unit based on personal use and representations made in commercial and technical sales literature The purpose of the compendium is not to identify the best or most desirable products rather it compares the features of the units to allow those unacquainted with this technology to better understand these features Remote afterloading is a rapidly developing field and new features may well have been added to these units by the manufacturers prior to the publication of this report Twenty items are identified and included in the compendium 1 Dose Rate ICRU Report 38 notes that low denotes conventional dose rates where the prescribed dose rate at the point of dose prescription is between 0 40 Gy h 0 0067 Gy min to 2 0 Gy h 0 033 Gy min medium denotes dose rates greater than 2 0 Gy h 0 033 Gy min and less than 12 0 Gy h 0 20 Gy min and high denotes dose rates greater than 12 0 Gy h 0 20 Gy min Pulsed remote afterloading under active development uses up to a 37 GBq 1 0 Ci Ir source for 10 to 30 minutes yielding instantaneous dose rates of 1 0 Gy h 0 017 Gy min to 3 0 Gy h 0 05 Gy min 2 Modality Intraluminal denotes irradiation
66. f design constraints some remote afterloaders may be unable to treat all anatomic sites Generally in planning capital budgets planners must not overestimate the number of patients available for treatment because they fail to understand exactly which types of manual brachytherapy may be replaced by remote treatment For example significant numbers of gynecologic patients often are treated with combinations of interstitial vaginal implants in conjunction with a conventional intrauterine tube such a combination treatment cannot be given on some low dose rate afterloading units designed for gynecologic therapy Moreover the number of patients treated yearly may be highly variable and determined by referral patterns that often reflect changes in staff physicians In high dose rate treatments of the lung one of the more popular procedures with HDR units some patients planned for intraluminal therapy cannot be treated because they cannot tolerate catheter placement In summary when planning to replace a manual brachytherapy procedure with a remote afterloading procedure careful retrospective reviews of prior patient treatments for several years are advised so realistic estimates of the numbers and exact types of procedures are obtained B Facility Design Low Dose Rate Units Facility design often is dictated by whether one is planning a new facility or renovating an existing facility to accommodate a remote afterloading device Renovation
67. f the publisher Published by the American Institute of Physics Inc 335 East 45th Street New York NY 10017 Printed in the United States of America The Charge to a Proposed Task Group on Remote Afterloading Systems Remote afterloading of radioactive sources for brachytherapy is becoming increasingly popular in the United States as evidenced by the increased sales of remote afterloading systems With low medium and high dose rate options these units offer the potential for superior dose distributions and the practical advantages of better radiation protection However as with any new technology these systems generate a host of new concerns that the users must address This task group addresses several of these concerns Currently there are no explicit protocols for source calibration Often calibration of these sources yields activities at odds with those provided by the manufacturers This need for a dosimetry protocol is particularly important for the high activity Ir sources which are exchanged frequently Remote afterloading systems present a unique set of radiation control questions particularly when the units fail to function adequately and the sources stick in the applicators The task group would suggest radiation control practices and quality assurance procedures for these systems Often existing hospital rooms or teletherapy vaults not originally designed for the remote afterloading systems are used to house these
68. gure 14 depend on the source to chamber distance Most reporting on in air calibrations of LDR and HDR sources neglect attenuation and multiple scattering of photons in air Read et al at the National Physics Laboratory adopted 0 2 per meter as the correction for attenuation and multiple scattering in air for Ra Co and Cs Hence at distance of 5 cm to 100 cm likely to be used for in air calibration of HDR sources neglecting air attenuation and multiple scattering is reasonable b The exposure gradient displacement corrections are required because of the finite dimensions of the chamber These corrections are greatest when the dosimeter size is comparable with its distance from the source and are least when the chamber dimensions are small relative to its distance from the source Spherical chambers exhibit 74 Figure 14 Radiation attenuation and scattering in a room A source S is near the center of the room detector D is mounted on a plastic support stand Top 1 primary ray 2 ray attenuated or scattered by air 3 ray scattered by air toward D 4 ray scattered by stand 5 ray scattered by floor 6 ray scattered by ceiling 7 ray scattered by wall The effects of rays 2 and 3 often are neglected Rays 4 7 constitute room scatter radiation Bottom A conical 3 TVL shield with a cross section sufficient to shield the source intercepts rays 1 and 2 Measurements in this geomet
69. h sources are exchanged They generally include but are not limited to 1 Procedures for receiving and returning sources allow adequate time after source exchange to prepare and ship the decayed source six weeks is a good time period 2 Frequency of leak testing usually every six months If sources are retained for a shorter period of time it is sufficient for the user to rely on the manufacturer s leak test provided it is recent enough 3 Frequency of inventory checks usually quarterly as remote sources are self contained it is possible to write alternate procedures in the license that substitute for a physical inventory 4 Specifications of radiation surveys to be made with each source change in order to a Ensure that all sources are either in the safe of the remote afterloader or in the shipment container 39 b Determine the exposure rate at agreed points around the safe These rates must be within the limits set by the regulatory licensing agency c Determine for exposed sources that the exposure rate at points outside the treatment room identified in the license application are within the limits set by that agency 5 If patients receiving multiple fractions are in therapy when a source change occurs it is particularly important to confirm that the newly established source activity is used for calculation of their treatment times 6 Frequency of dose rate measurements in and around areas whe
70. hamber The block should have a small conical cross section and be placed as close as possible to the source but fully shield the chamber As the block will transmit only 0 1 of any incident radiation measurements above that 77 Table 4 Values of factor K the ratio of measured exposure rate to true exposure rate for cylindrical chambers with sideward positioning of sources a is cavity radius dis the distance from the source to the center of the cavity L is the cavity length DISTANCE FACTOR a a d 0 01 0 1 000 0 005 0 927 0 007 0 870 0 01 0 785 0 03 0 416t 0 05 0 275 0 1 0 147 0 5 0 0310 0 9 0 0173 ok SHAPE FACTOR o a L 0 1 1 000 0 9992 0 998t 0 997 0 972 0 162 0 15 1 000t 0 9986 0 987t 0 966 0 8824 0 234 0 25 1 000 0 4375 0 8497 1 0981 Approximate value based on K A tan A where a o For complete table see S Kondo and M L Randolph Rad Res 13 47 1960 Table entries are approximate values calculated from A tan A other entries are from the original article 78 represent room scatter contribution As room scatter may well be only 0 1 to 05 of the measured charge depending on the room size and the source chamber location these shielded measurements must be done with greater care to obtain a charge signal above that contributed by leakage charge Ezzel describes an alternate measurement of room scatter Assuming room scatter is a
71. he generally accepted standard of positional accuracy is I mm 11 Source Arrangements How are different source arrays achieved Methods included oscillating one or more sources pre loaded source trains pencils active and inactive pellets that can be interchanged and stepping sources 12 Uses Conventional RTP Radiotherapy Treatment Planning Software for Dosimetry How are isodose distributions obtained Can one use a commercial RTP computer for isodose computations or must other dedicated computers or other techniques preplanned isodose atlas be employed 13 Dose Optimization Available Is there dose optimization software available with the device 14 Bladder and Rectal Dosimetry Does the unit offer a method of measuring these doses Some devices offer low activity pilot or test sources designed for such dosimetry 15 Source Container Maximum Storage Activity What maximum activity in megabecquerels curies of Cs Co or Ir can be stored in the unit In any secondary storage unit 16 Special Features What is unique about the unit 17 Number of Applicator Channels How many channels does the unit have 18 Maximum Number of Sources in Device How many different radioactive sources can be stored in the unit at one time 19 Maximum Number of Channels Used Simultaneously How many of the available channels can be used at the same time 20 Sources Available Which radioisotopes are available What is t
72. he control console or nearby area and at a minimum 1 Describes the functioning of the control console options 2 Describes how to program a treatment and supplies a sample program 3 Describes how to check that the program and time adjustment factor if applicable are correct 4 Describes emergency procedures these shall also be posted 5 Provides a list of names and telephone numbers of people to contact in case of an emergency these shall also be posted 6 Provides a check list of quality assurance procedures to be performed and the name and number of the person to call if quality assurance is not acceptable 7 Provides a list of error messages if applicable A Physicist Engineer Manual should be easily accessible that at a minimum 1 Describes radiation survey procedures when receiving new sources 37 2 Describes procedures for returning old sources 3 Describes source change procedures 4 Provides a floor plan for room surveys to be performed 5 Provides a plan and check list of other radiation surveys to be performed 6 Provides a check list and forms for quality assurance procedures to be performed 7 Provides names and telephone numbers of people to calf in case of an emergency 8 Describes source calibration procedures and provides forms for calibration If nurses have a responsibility for operating a remote afterloading unit a Nurse s Manual should be at the control console which
73. heir physical form size and individual source activities Other parameters not included in Tables I and II but that are features of some units include a Memory for Standard Treatment Positions Can selected treatments be stored in memory for future treatments to be performed at a later date e g for a repeat treatment of the same source configuration required with fractionated therapy or for use on a series of patients requiring the same treatments b Safety Features How are applicator connections checked Is there a back up timer of any type How is the source position confirmed c Dummy Runs To Check Applicators Prior to Treatment Can the unit mechanically or electronically check applicator connections and insure the right combination of applicators and source guide tubes before treatment commences D Remote Afterloading Devices Table 1 lists six remote afterloading devices with low or medium dose rate features one high dose rate device and one pulsed dose rate device The Afterloading Buchler unit now marketed by STS Steuerungstechnik Strahlenschutz GmbH features an oscillating cam that moves a single source over 20 cm length to produce variable radiation distributions For treatment of gynecologic cancers two stationary sources are used as colpostat sources with the oscillating cam moving the tandem source to provide a 3 channel system This unit has an option for interchange between LDR and HDR operating modes if
74. her where the actual measurements are made allow adequate time for the well chamber to reach equilibrium temperature with the air in the room D Ionization Chamber Calibrations of LDR and HDR Sources Source calibration techniques using NIST or ADCL calibrated 68 spherical or cylindrical chambers in air water or water equivalent media have been described for LDR remote sources by Meertens Pipman et al for HDR sources in Gamma Med units by Bruggmoser et al Buffa and Cerra and Rodgers and HDR sources in the MicroSelectron by Ezzell and Jones and Bidmead Jones Flynn and by Goetsch and Attix and Goetsch et al If appropriate dosimetry corrections are made calibrations in air water or water equivalent media yield equivalent results 0 1 Calibration Factors Obviously Co and Cs LDR and HDR source s would be calibrated with an ion chamber and build up cap calibrated for the particular radionuclide of the LDR or HDR sources s Chamber calibrations for Co and Cs are available from NIST and ADCL laboratories 1 but no such calibration is available for Ir Methods of obtaining an ion chamber calibration for Ir are under active investigation Ezzell obtained a Ir calibration factor by interpolation between chamber calibration factors for Co with its build up cap and for superficial or orthovoltage photon energies without a cap calibration factors were plotted against
75. hylmethacrylate PMMA e g lucite perspex plexiglass acrylic using a Ir source They concluded that polystyrene and solid water are equivalent to water even if a full scattering phantom is not used However the more dense PMMA provided more attenuation of primary radiation which is compensated for by an increase in scatter under full scattering conditions without a full scatter medium PMMA is not truly water equivalent The free air exposure rate measured in a medium is given by 10 with P equal to unity i e no room scatter corrections are required The dose rate at a point r 8 in the medium is Daea t9 X mea 1 8 W aic Heal PJE Ac Pawai Gy s 22 which is similar to Equation 19 except 4 is the displacement factor similar but not identical to the equilibrium thickness attenuation correction A in the medium and the effects of attenuation and scattering in the medium F t 8 are inherent in the measured data 91 The free air exposure rate X is X r re R s 23 where f a the f factor for the medium is given by font Hea P 25 W e ai Gy R 24 Ezzell notes that in air and in phantom calibrations have agreed to within 2 for Ir sources when all correction factors are applied carefully Ix ISODOSE COMPUTATIONS Accurate dose computations for LDR MDR and HDR remote afterloading sources in an applicator in a patient depend on a knowledge of the dosimetry of
76. i T Sonoda and T Kasamatsu High Dose Rate Intracavitary Irradiation in The Treatment of Carcinoma of The Uterine Cervix Early Experience with 84 Patients Int J Radiat Oncol Biol Phys 14 893 898 1988 T Teshima M Chatani K Hata and T Inoue High Dose Rate Intracavitary Therapy for Carcinoma of the Uterine Cervix II Risk Factors for Rectal Complications Int J Radiat Oncol Biol Phys 14 281 286 1988 C Shu Mo W Xiang E and W Qi High Dose Rate Afterloading in The Treatment of Cervical Cancer of The Uterus Int J Radiat Biol Oncol Phys 16 335 338 1989 R G Dale The Use of Small Fraction Numbers in High Dose Rate Gynecological Afterloading Some Radiobiological Considerations Brit J Radiol 63 290 294 1990 K K Fu and T L Phillips High Dose Rate versus Low Dose Rate Intracavitary Brachytherapy for Carcinoma of the Cervix Int J Radiat Oncol Biol Phys 19 791 796 1990 C A F Joslin Brachytherapy A Clinical Dilemma Int J Radiat Biol Oncol Phys 19 801 802 1990 W E Livevsage Dose Rate Effects in Institute of Physical Sciences in Medicine Report 45 Dosimetry and Clinical Use of Remote Afterloading Systems ed A R Alderson Institute of Physical Sciences in Medicine London 1986 1 8 98 34 35 36 37 38 39 40 International Commission on Radiation Units and Measurements Report 38 Dose and Volume Specifications for Reporting Intracavitary Ther
77. imited to having available in the treatment facility 1 An emergency container Fire 5 and long handled tongs for retrieving the source s if it they break s from the drive mechanism or fail to return to the primary safe This emergency container should be large enough and deep enough to accept the entire applicator assembly that is in a patient if it is ever necessary to remove an entire applicator with sources intact in it During treatment the 34 Fire 5 A mobile emergency shielded container Long handled forceps to assist with source retrieval should be available with the container Courtesy of Mick Radio Nuclear Inc NY 35 container must be positioned sufficiently close to the patient so that it can accept the applicator with source intact in it if necessary Medical supplies and devices to assist with emergency applicator removal should be available 2 A radiation survey meter 3 A sign DANGER DO NOT ENTER OPEN SOURCE for immediate posting if required Documented exit radiation surveys of patients which may seem redundant are still good practice and may be required by license to confirm there are no sources in the patient depending on the regulatory agency and license application content An independent visible radiation detector in the room generally is required and may serve as the exit survey device However it must have sufficient sensitivity to respond to the smallest individual radioactive s
78. ing keys door interlocks radiation warning systems and for HDR units in linac 31 vaults ensure that any other device that produces radiation cannot be turned on simultaneously with the HDR unit 9 Describe patient viewing and communication systems 10 Describe the detection instruments calibration procedures calibration frequency leak test procedures and frequency and the qualifications of those performing these tests 11 Describe the quality assurance program including either pre treatment or daily quality assurance procedures and procedures to be performed at other selected monthly quarterly annually intervals 12 Describe the training of individuals performing the source changes normally vendor representatives 13 Describe the training and frequency of retraining of individual operators Annual training may be excessive retraining at two years is more reasonable 14 Describe the personnel radiological monitoring program Quarterly badge changes may be adequate 15 Describe the emergency procedures where they are posted and the frequency of emergency dry runs 16 Describe provisions of disposing of decayed sources usually by return to vendor 17 Describe the titles and locations of manuals available to personnel License Compliance You must do what you promise in your license so caution is advisable you can always do more but never less For example calibration and 32
79. ingle nursing staff unit can be better trained and patients generally receive better care For the Radiation Safety Officer there are distinct regulatory and procedural advantages from having a single group of nurses for whom training records and personnel exposure records must be maintained and for whom initial continuing and annual instructions in radiation safety must be given High dose rate remote afterloading devices yield dose rates greater than 0 2 Gy min doses of several gray generally are delivered in minutes High dose rate remote afterloading is particularly appealing to facilities with large patient populations they if treated by conventional manual LDR brachytherapy would require prolonged hospitalizations Treating these patients as outpatients using multiple fraction treatment regimens on a remote HDR device is appealing to the patients Free standing radiation therapy centers that do not provide hospital rooms find HDR units appealing A dedicated HDR treatment suite with an overhead x ray tube and fluoroscopy can accommodate many patients yearly large workloads are possible on a single unit There is little radiation exposure to attending medical personnel and none to adjacent patients adjacent patients receive radiation exposure with manual LDR or remote LDR afterloading Applicators can be rigidly secured for the short treatment times common with HDR therapy consequently undesired applicator movement observed during pro
80. l Phys 24 167 170 1992 M B Podgorsk L A DeWerd B R Thomadsen and B R Paliwal Thermal and Scatter Effects on the Radiation Sensitivity of Well Chambers Used for High Dose Rate Ir 192 Calibrations Med Phys 19 1311 1314 1992 H Meertens A Calibration Method for Selectron LDR Sources in Brachytherapy 1984 Nucletron Trading BV Leersum the Netherlands edited by R F Mould Nucletron Trading BV Leersum the Netherlands 1984 58 67 103 74 75 76 77 78 79 80 81 Y Pipman A Jamshidi A Sabbas Commissioning of a Selectron LDR Remote Afterloader Tests and Measurements Med Phys 16 494 1989 Abstract G Bruggmoser K Kuphal U Freund M Wannenmacher Dosimetry of the Afterloading Therapy with Gamma Med in Proceedings of the First International Meeting of Gamma Med Users edited by S M Shah Mick Radio Nuclear Instruments Inc New York NY 1986 154 159 A Buffa Gamma Med II Source Calibration Employing Tonometric Techniques in Proceedings Second Annual International High Dose Rate Remote Afterloading Symposium Health Physics Consultants South China ME 1987 77 81 G A Ezzell Evaluation of Calibration Techniques for the MicroSelectron HDR in Brachytherapy 2 Proceedings of the 5th International Selectron User s Meeting edited by R F Mould Nucletron International BV Leersum The Netherlands 1989 61 69 G A Ezzell Evaluati
81. l cm are allowed The desired dose distribution is achieved by allowing different dwell times at each location Model Ii of this unit features an indexer with twelve channels into which a single 370 GBq 10 0 Ci Ir source can be moved sequentially for interstitial implants a new unit Model 12i contains twenty four channels and allows forty steps of 0 l cm to l cm increment over 40 cm length AU of the devices listed feature numerous fail safe systems to ensure safe operation and use numerous popular applicators adapted for remote operation IHI PATIENT POPULATIONS EQUIPMENT SELECTION AND FACILITY DESIGN A Patient Populations and Equipment Selection Selection of a particular remote afterloading device will depend on the types and numbers of patients to be treated total project costs and funds available and the radiation oncologists current treatment philosophies and willingness to adopt new methods of patient care Obviously facilities with large patient numbers 100 patients per year or greater may find remote afterloading more practical and the costs less burdensome than facilities with small patient numbers Some of the types of brachytherapy and common anatomic sites treated with remote afterloading devices are intracavitary uterus vagina rectum intraluminal esophagus bronchus trachea interstitial breast chest wall head and neck vaginal sidewall pancreas and surface skin lesions treated with molds Because o
82. le in the room as patients can have numerous additional electrical monitors each requiring its own power Generally existing hospital rooms often are too small to accommodate ancillary equipment such as x ray tubes and anesthesia equipment which one may consider having in a new facility For a low or medium dose rate unit it is imperative to know the maximum amount of radioactive materials and type to be used at one time and their duration of use e g length of treatment sessions and the projected workload of the unit Licensing the facility will generally require compliance with the three traditional requirements of the USNRC and its Agreement States namely that the dose equivalents in adjacent unrestricted areas be 1 less than 0 02 mSv 2 mrem in one hour 2 less than 1 mSv 100 mrem in 7 days and 3 less than 5 mSv 500 mrem in one year The recent NCRP and ICRP recommendations of 1 mSv 100 mrem annual effective dose equivalent for members of the general public continuously frequently exposed to radiation have been adopted by the USNRC with 5 mSv 25 500 mrem allowed by license authorization Realistic estimates of the maximum amounts of radioactive materials to be used for specific durations are required in satisfying these conditions In a new facility it may be possible to include in the treatment suite other desirable ancillary equipment Table 3 such as dedicated localization equipment required to
83. libration under AAPM approved protocols of similar HDR well type ionization chambers purchased by users for calibration of their Ir HDR sources of identical design to the source used to calibrate the ADCL well ionization chambers Can conventional nuclear medicine or brachytherapy well ionization chambers be used to calibrate HDR sources One major difference between LDR and HDR sources is the magnitude of the currents they generate in ion chambers The HDR sources with activities as large as 740 GBq 20 0 Ci obviously yield much higher currents than 740 MBq 20 0 mCi LDR sources The well ionization chamber electrometer current range and linearity determine if the well ionization chamber can be used with HDR sources For example the RADCAL Model 4050 well ionization chamber is calibrated from 4 5 fA to 225 nA and the maximum current of 225 nA is produced by a 185 GBq 5 0 Ci Tc source yielding 4 5 nA per curie of Tc Using stated calibration factors for this chamber the maximum activity of Cs measurable would be about 92 5 GBq 2 5Ci for Co the maximum activity measurable would be about 25 9 GBq 0 70 Ci for Tr 111 GBq 3 0 Ci appears to be the upper limit Hence a careful 64 review of the user s manual should identify whether a particular well ionization chamber electrometer can accommodate the hi currents provided by HDR sources one needs to calibrate A well insert can be designed with about 2 cm diameter cylind
84. longed hospital stays required with LDR brachytherapy is reduced In some instances the HDR remote afterloading sources can be configured more advantageously yielding more desirable dose distributions than those achieved with conventional LDR radioactive sources and manual afterloading In treatments of some gynecologic cancers with HDR units urinary catheters are not required as with conventional treatments Vaginal packing requirements often are less Hence HDR therapy is an appealing alternative to LDR therapy in treating gynecologic malignancies Finally the very small diameter about l mm high activity 148 0 GBq 4 0 Ci to 740 0 GBq 20 0 Ci Ir sources in HDR remote afterloading units allow treatments of interstitial and intraluminal sites esophagus bronchus bile duct brain etc previously untreated or treated only with difficulty with conventional LDR manual afterloading techniques Medium dose rates are those between low and high dose rates several 10 Gy doses can be delivered in several hours Interest in MDR remote brachytherapy is less pronounced than interest in HDR remote brachytherapy B Disadvantages of Remote Afterloaders Remote afterloaders are not free of disadvantages The devices require a modest capital expenditure of 150 000 to 300 000 and the cost of renovating a conventional hospital room to accommodate an LDR unit is probably 50 000 to 100 000 An HDR suite is more costly a dedicat
85. me design A well ionization chamber may be used to determine relative activities as long as each individual source in the batch is measured in an identical manner e g at the same position in the center of the well ionization chamber Multiple autoradiographs of each source on one film and a comparison of relative optical densities is an alternate method but requires greater attention to procedural detail 3 Leak testing of the source s Swabs or filter papers moistened with water or alcohol are used to wipe either the source surface or the interior of the selected source carrier Activity can be measured with calibrated GM tubes or scintillation counters that can detect 37 Bq 1 0 nCi Often indirect leak testing is required by testing the interior of applicators or source guide tubes directly in contact with the source rather than direct leak testing of the source s Generally the extent of leakage from a sealed non gaseous source is estimated by multiplying the measured activity obtained by a factor of 10 Normally sources that have less than 185 Bq 5 0 nCi removable activity on their exterior surface are considered uncontaminated 4 Determination of dose distribution anisotropy Source construction and encapsulation generally produce dose distributions that are anisotropic particularly near the ends of small linear sources Figure 10 Often these effects are neglected and the sources are considered point sources for dose c
86. minimize scattering Figure 13 Source and chamber should be near the center of a large room and well above the floor to minimize any contribution from room scattering The same location in the room with the same equipment about should always be used for subsequent calibrations of the source or replacement sources so that the room scattering effects if any are constant Large volume ion chambers are better than the conventional 0 6 cm cylindrical Farmer type chambers Buffa notes that 3 cm ion chamber yields 1 pA 40 cm from a 370 GBq 10 0 Ci source Ezell notes that 0 6 cm ion chambers can yield 5 pA at 20 cm from a 300 GBq 8 10 Ci source As long integrated charge collection periods may be required leakage charge should be measured and corrections made to the integrated charges measured To minimize leakage use low noise electrical cables allow long electrometer warm up times and keep cable lengths short to minimize the lengths of cables exposed to radiation Depending on ion chamber volume and collection efficiency in air charge measurements may be made a few centimeters from the source and up to l m from the source For LDR sources the low current necessitates measurements at closer distances which is why well ionization chamber measurements are preferred Measurements made close to the source exhibit higher charges shorter end effect timer 71 Figure 13 a Calibration fixture designed to minimize radiation s
87. mulated charge in coulombs corrected for leakage but not corrected for chamber dose gradient or room scatter effects t the duration of charge collection in seconds a the end effect timer error in seconds a transit time of the source s and a function of d C the conventional temperature and pressure correction for ionization chambers the correction for the collection efficiency of the electrometer chamber at calibration ion p_ the correction for the collection efficiency of the electrometer chamber at the time of the study 81 P a the exposure gradient displacement correction Pao the room scatter correction X X X N _ the calibration factor for the ion chamber electrometer at calibration conditions in roentgens per coulomb From the free air exposure rate X r one can then obtain the collisional air kerma rate at r K r Kur A O W e a Gy s 12 with X r in R s in air and W e in air is the mean energy expended per unit charge released in dry air W e 33 97 J C 87 6 Gy R Although the primary goal is to measure a source strength for use in clinical dose calculations a secondary goal is to derive a strength value that can be compared to the manufacturer s stated calibration of the source As the calibration certificate may state activity in megabecquerels curies apparent activity in milligram radium equivalent or air kerma rate uGy h at a reference
88. must be satisfied Dove provides illustrative examples of the correction for this geometry and additional equations for other geometries Kondo and Randolph provide similar corrections K in which a distance factor equal to the ratio of chamber cavity radius a to the distance d of the chamber s center from the source of radiation is expressed as a function of the shape factor equal to the ratio of chamber radius 1 to chamber cavity length L K is the ratio of the measured exposure rate to the true exposure rate conceptually identical to Dove s correction Table 4 a partial table applies for cylindrical chamber positions perpendicular to the source Kondo and Randolph provide an additional table for another chamber source geometry For a given chamber and source geometry Dove s equation and Table 4 an expanded version of Kondo and Randolph s Table 1 provide similar corrections c Room scatter includes reflective contributions from all surfaces in the room including the chamber holding stand Often room scatter is assumed to be a constant contribution to the integrated charge independent of the chamber to source distance However this is likely true only if the chamber and source are both about 2 m from scattering surfaces Buffa investigated room scatter using three tenth value layer shield block on a mobile stand Figure 14 and positioning the shielding block between the source and the ion c
89. ns as the source to chamber distance was changed by accurately known amounts using the drive mechanism of a beam scanning system 70 Following the methodology of Goetsch et al if the measured distance is in error by an amount c then d d c m 7 where d the effective center to center source chamber distance d the measured source chamber distance with an arbitrary but constant offset C the correction or error in the distance Assuming the same amount of room scatter radiation M is included in each integrated charge reading M then M M M C 8 d where M is the integrated charge reading due only to primary radiation At each nominal distance d a constant f independent of d is f M ed M M e d4 cy m2 C 9 Any group of three equations made at three or more distances can be used to solve for the three unknowns f c and M The quantity f is 80 combined with the exposure rate constant and with the chamber s exposure calibration factor to determine the source strength d Calibration data at a single source to chamber distance may be obtained by measuring the charge rate current or charge collected in an interval of time Following the dosimetry concepts of Attix the free ah exposure rate X r at a distance r from the source can be calculated from X t M Crp Aia Pia Pera Prs Nx R s 10 where me S c s fat and M_ the accu
90. ntracavita Intralumina Interstitial Cs 8 to 6mm Co 8 4 3 15 22 mm mir G S 4 3 15 and 2 2 mm Sources mechanically auto connect to ball chain Oscillating cam moves one source over 20 cm two sources remain fixed Gravity fallin weight e 3 in unit and 3 in source changing container No Munich Paris Bejing Manchester Stockholm Rome Fletcher Interstitial Not stated in commercial literature Cam oscillates tandem source and two stationary sources to field preselected Atlas distribution No uses isodose atlas No Treatment terminates at present dose on detectors used during treatment Low Medium High Intracavitary Cs 4 2 to 3 2 mm Sources auto connect to drive cable None static Backup battery and safety device 10 or 20 preloaded trains in mobile safe No Detouche Chassagne Fletcher Henschke Not stated in commercial literature Preloaded sources arranged to give desired distnbution Conventional arrangements Yes using point source programs isodose atlas MicroSeectroa LDR Nucietroa Engiereing BY Netherian Low Intraluminal Interstitial mir 1S mm PCs 1 9 mm Sources auto connect to drive cable monitored by microprocessor Pneumatic microprocessor controlled Source Trains with 48 pellets 120 mm any pellet may be programmed to be active inactive Stationary linear sources or seed arrays Back up ba
91. of existing patient rooms is most common for LDR units Low dose rate remote afterloading units usually can be located in rooms used for manual afterloading Figure 1 Corner rooms adjacent to electrical closets or stairwells are ideal if the regulatory licensing agency allows use of occupancy factors less than one for these areas The room should be close to the nurses work station to minimize long cable runs for remote alarm systems and to allow visual surveillance by the nurses of the entry doorway if possible to minimize interruptions in therapy While bedside shields commonly used for manual afterloading procedures can be used in conjunction with remote afterloading units Figure 2 they offer several practical disadvantages In smaller rooms there is little space remaining around the bed if both the LDR 20 l ELEVATOR SHAFT o U T REMOTE s CONTROL t TO NURSES D E CURTAIN REMOTE CONTROL 172 LEAD ON ORYWALL DEDICATED POWER OUTLET COMPRESSED b Hi AIR SUPPLY STAIRWELL SCALE 1 2 Figure 1 A small 11 by 9 second floor hospital room renovated at a cost of 59 000 to house an LDR remote afterloading device for gynecologic treatments Courtesy G P Glasgow Maywood IL This room features an internal storage closet in which the LDR unit is stored when not in use A projection shield 1 2 lead beneath the bed shields the area below 1 4 lea
92. omputations Generally the user should determine if the dose anisotropy for a specific model source has been measured Measuring dose distribution anisotropy is difficult and few reports exist Cerra and Rodgers measured dose anisotropy for a Gamma Med Ili high activity Ir source dose anisotropy in low activity Ir seeds was reported by Ling et al and C Thomason et al as well as for Cs seed sources Siwck et al reported on the dose anisotropies produced by adjacent spherical Cs sources in a Selectron 55 7 135 af A Sag j 135 aT y 165 pee 165 Figure 10 Measured isodose rate contours in water for a 370 GBq 10 0 Ci 0 5 mm by 5 5 mm Ir Gamma Med II source in an endobronchial applicator The respective intensities starting from the center arc 1146 509 285 125 68 and 42 cGy hr Ci Axes arc labeled in centimeters Courtesy of F Cerra and J F Rodgers Washington D C 56 Users should determine by measurement if possible or by review of the literature the dose anisotropy of specific source models Data for dose distribution anisotropy should only be used for the specific model sources reported and not applied to other sources 5 Absolute calibration of the source s For remote afterloaders using single Ir sources replaced several times yearly it is most important to develop a consistent reproducible method of calibration For long lived sources e g Cs pellets where
93. on of Calibration Techniques for a High Dose Rate Remote Afterloading Iridium 192 Source Endocurietherapy Hyperthermia Oncology 6 101 106 1990 C H Jones and A M Bidmead Calibration of the MicroSelectron HDR System in Brachytherapy 2 edited by R F Mould Nucletron International BV Leersum the Netherlands 1989 75 82 A Flynn Quality Assurance Checks on a MicroSelectron HDR Selectron Brachytherapy Journal 4 112 115 1990 S J Goetsch and F H Attix Ir Remote Afterloading Source Calibration AAPM Newsletter 15 No 1 3 1990 104 82 83 84 85 86 87 88 89 90 G A Ezzell The Effect of Alternative Calibration Procedure using the NFL 2505 3 Ionization Chamber A Brief Communication Selectron Brachytherapy Journal 5 42 43 1991 L R Read J E Bums R A C Liquorish Exposure Rate Calibration of Small Radioactive Sources of Co Ra and Cs Int J Appl Radiat Isot 29 21 27 1978 D B Dove Effect of Dosemeter Size on Measurements Close to a Radioactive Source Brit J Radiol 62 202 204 1959 V S Kondo and M L Randolph Effect of Finite Size of Ionization Chambers on Measurements of Small Photon Sources Radiation Research 13 37 60 1960 A F Bielajew An Analytic Theory of the Point source Non uniformity Correction Factor for Thick walled Ionization Chambers in Photon Beams Phys Med Biol 35 517 538 1990 H Tolli Ioniz
94. or material composition of the central axis insert source holder may also alter chamber response Central axis positional dependency Figure 12 of well chambers has been reported by numerous authors The positional dependency also is energy dependent and must be measured for each radionuclide Usually source holders can be designed to accurately reposition sources 65 RELATIVE RESPONSE OF WELL CHAMBER 40 1 125 6702 30 O 1 425 6711 20 Au 198 aa WAGE gf C8137 pg 206 1 0 e 10 20 40 60 80 100 200 400 600 800 1000 AVERAGE PHOTON ENERGY keV Figure 11 Energy dependence of Ar filled well ionization chamber Responses are normalized to that of Ra 6702 and 6711 are model number of CA 125 I sources Courtesy of K A Weaver San Francisco 66 1 1 09 RELATIVE READING Raneedie 1mg o oe Cs tube 5 mg em Irseed 0 5mg a A seeds 40 mCi 6702 and 1 3 mCi 6711 07 1 2 3 4 5 6 7 8 9 10 11 12 DISTANCE FROM WELL BOTTOM cm Figure 12 Variation in response of well ionization chamber with vertical position along the well axis for several radionuclide sources Courtesy of K A Weaver San Francisco CA 67 at specific locations along the central axis where the positional dependency is least The well chambers designed for HDR sources exhibit a heat dependency e g the 370 GBq 10 0 Ci sources can increase the air temperature in the collection w
95. ource used in the device at the maximum distance the source could be from the detector A hand held Geiger Mueller survey meter is best for exit surveys Finger radiation monitors for personnel operating units are a good practice While unusual events such as a source jammed in the applicator are infrequent if personnel are involved in an emergency their finger rings in conjunction with their whole body personnel monitors will help provide estimates of dose equivalents received during emergencies Posted emergency procedures should address the appropriate sequence of actions if the source s fails to retract and explain the next sequence of actions if the first corrective action sequence fails to retract the source s e g describe what actions to take if the source s fails to retract when the emergency off is pushed describe what sequence of actions to follow if the mechanical retraction system fails describe who to call next if no one responds at the first emergency number called etc 36 Finally well described procedures should exist for source s retrieval if the source totally detaches from its drive mechanism and falls to the floor or remains in an applicator in the patient Particular care must be given to emergency procedures for HDR sources because the exposure rates are so high Exposure rates l m from an unshielded 370 GBq 10 0 Ci Ir source are about 4 6 R h D Manuals An Operator Manual should be at t
96. re sources in remote afterloading units or supplemental safes are stored when not in use E Emergency Procedures Some emergency procedures have previously been discussed under routine procedures e g that plans should be made for emergencies In preparing emergency procedures it is important to have separate procedures established for electrical power loss emergencies fire ii the treatment facility or in the remote afterloading device emergencies and radiation emergencies For the latter typical emergencies include 1 source s failing to seat in the applicator aborting the treatment 2 potential interruption of the therapy because the sources dislodge from the applicator the applicator dislodges from the patient or a source guide tube becomes loose or ruptures 3 clock or timer failure during therapy 4 at the end of therapy the source s fail to retract and 5 the sources or source capsule break away and spill the radioactive material in the room A major emergency would be losing a source in the patient e g some accident in which the applicator fails and the source breaks loose and lodges in the patient Some consider ation must be given to the actions required if this were to occur While open ended catheter procedures have been used with remote 40 afterloading units they are not recommended because of the small possibility of losing a source within a patient Procedures exist for placing opened ended c
97. rm the length to l mm accuracy For pneumatic transfer of sources air tubes must be inspected for hairpin leaks constrictions and other obstacles to source transport Particular care should be given to testing the remote afterloader with all combinations of source transport tubes and applicators to ensure that faulty connectors do not exist 45 2 The mechanical integrity of the applicators via visual inspection and or radiographs Confirm the presence and correct placement of any internal shields or other critical internal components within the applicator 3 That any simulated dummy source designed to represent source position or placement and the radioactive source s both position properly generally to l mm accuracy in applicators or at static locations in test devices Radiographs of dummy sources in test devices or applicators Figures 6 7 with their mechanical positions indicated by pen pricks or other external markers if possible combined with autoradiographs of the radioactive source s in the same device or applicators will show any lack of coincidence between the position of the dummy sources and the position of the radioactive source s Ezzell describes a device with eighteen channels Figure 8 used for autoradiography Jones uses a strip of radiation sensitive paper for autoradiographs For simulated sources and radioactive sources one can observe by CCTV and transparent source placement check devices Figure 9
98. ry include room scatter contributions rays 4 7 and the multiple scatter ray 3 from air Courtesy of G P Glasgow Maywood IL 75 smaller displacement corrections than cylindrical chambers Dove and Kondo and Raldolph provide protocols for these corrections which can vary from about 1 2 at 10 cm to 0 1 at 40 cm for a 0 5 cm cylindrical Farmer type chamber Bielajew reviewed the theory of these corrections extending the work of Kondo and Randolph Tolli investigated the displacement effect at 20 mm source chamber distance for Ir Co and Cs For an idealized cylindrical chamber Figure 15 with a cavity of radius a and length 2h located a distance X from the source with its length perpendicular to X Dove determined that the ratio of the measured exposure rate D X a 2h to the true exposure D X is given by 2a Xord Lor 2h SOURCE DOSEMETER Figure 15 Source cylindrical chamber geometry for exposure gradient displacement corrections The letters in lower case denote parameters used by Dove those in upper case are the parameters used by Kondo and Randolph The source to center of chamber distance is X or d the chamber cavity diameter is 2a the chamber cavity length is 2h or L 76 1 1 X h 3 22 2 D X a2h 1 X h4 5 2h a 3 a 3 4 DOD L 1 X5 R 7 Th a 20 hat 9 af 4 where the condition k lt XV 2X 4a X a 5
99. se involving chamber calibration at multiple distances 5 The accuracy of any decayed source s activity calculated by computer Decayed source activity tables should be available to confirm source activities calculated by the remote afterloading unit 6 That any multi channel indexer functions properly and moves the source s in proper sequence into the correct channels 43 7 That appropriate backup systems function properly during simulated power failures and or air pressure losses 8 That the mechanical source retraction system works it may not be possible to simulate an exposed source condition on some units 9 That any radiation detectors in the remote afterloader operate properly 10 That program storage and recall function properly Check that dwell times in stored programs are changed to reflect source activity at the time of use unless the machine design requires entry of dwell time patterns based on a given activity e g 370 GBq 10 0 Ci with automatic adjustment of the real treatment time to allow for decay 11 That leakage radiation rates around the device are acceptable B Facility Testing Facility testing includes but is not limited to confirming 1 That any door interlock system retracts the source s when the door is opened and that the unit does not restart automatically when the door is closed 2 That the source s cannot be driven out of the safe with the door open 3 That radiation
100. signs of devices on this Registry 30 B License Content With respect to the license application content include only the absolute minimum information required The license and any attached documents is a legal standard against which compliance actions will be judged Quality assurance procedures that you intend to do faithfully at regular intervals should be excluded unless required by the regulatory agency A typical license application must 1 Describe the source s radionuclide size manufacturer ac tivity and physical construction 2 Describe the manufacturer and model of the remote afterloader 3 Describe the intended use cancer therapy in humans 4 Describe the intended users and their training and experience 5 Describe the radiation detection instruments to be used 6 Describe to scale the floor plan of the facility identifying the doors windows wall materials and distances to closest occupiable points around above and below the facility 7 Prove by calculations that selected adjacent areas comply with the required regulatory standards likely to be 0 02 mSv 2 mrem in one hour 1 mSv 100 mrem in seven days and 5 mSv 500 mrem in one year for non restricted areas and 1 mSv 100 mrem in one year for members of general public continuously exposed The 5 mSv 500 mrem per year may be allowed by license authorization by the USNRC 8 Describe area security including access to operat
101. stitute of Physics New York 1984 40 43 L N Berkley W F Hanson R J Shalek Discussion of the Characteristics of the Results of Measurements with a Portable Well Ionization Chamber for Calibration of Brachytherapy Sources in Recent Advances in Brachytherapy Physics edited by D A Shearer American Institute of Physics New York 1981 38 48 102 66 67 68 69 70 71 72 73 A L Boyer P D Cobb K R Kase and D J S Chen 92Ir Hospital Calibration Procedures in Recent Advances In Brachytherapy Physics edited by D A Shearer American Institute of Physics New York 1981 82 103 J F Willamson R L Morin F M Khan Dose Calibrator Response to Brachytherapy Sources A Monte Carlo and Analytic Evaluation Med Phys 10 135 140 1983 A Niroomand Rad Routine Calibrations of Brachytherapy Sources with a Well Type Dose Calibrator Using Standard Calibrated Sources Radiat Med 8 238 245 1990 K A Weaver L L Anderson J A Meli Source Calibration in Interstitial Brachytherapy Interstitial Collaborative Working Group Raven Press New York 1990 15 19 S J Goetsch F H Attix D W Pearson B R Thomadsen Calibration of Ir High Dose Rate Afterloading Systems Med Phys 18 462 467 1991 S J Goetsch F H Attix L A DeWerd and B R Thomadsen A New Re Entrant Ionization Chamber for the Calibration of Ir 192 HDR Sources Int J Radiat Oncol Bio
102. te The MINIRAD features sixteen channels is particularly applicable for LDR interstitial therapy of the breast and prostate and is designed to be disconnected from the patient once the initial source transfer is complete Each patient has a dedicated source container and the unit can track up to fourteen different containers The LDR Inter Pal C 38 features thirty eight channels and also is designed to be disconnected from the patient once source transfer is complete This unit allows the operator to use an electronic remote control device for source transfer By the nature of their design the 17 MINIRAD and Inter Pal C 38 do not retract sources when personnel eater the patient s room after the procedure begins The I amp channel MicroSelectron PDR uses a 37 GBq 1 0 Ci Ir source to yield instantaneous dose rates up to 300 cGy h which when pulsed i e delivered in a few minutes during each hour are believed equivalent to continuous low dose rates of about 50 cGy h Eight high dose rate devices are included Table 2 The Ralston 20B unit available in Japan was omitted as as no units have been sold in the United States Afterloading Facts Buchler unit is a general purpose unit for interstitial intracavitary intraluminal and intraoperative therapy It has a twelve channel indexer and can be loaded with either a point source l mm xX l mm active volume Ir or with a linear source 0 5mm x 5 mm active volume
103. te walls specific density 2 2 g cm for a 370 GBq 10 0 Ci Ir source Figure 4 Bourland describes for a Buchler HDR unit a vault 8 m 26 Table 3 Equipment List Dedicated Remote Afterloading and Minor Procedures Suite Anesthesia area Medical gases and vacuum designated location and electrical power for patient monitoring equipment remote displays Audio communications Visual communications 2 systems e Sink scrub area Patient procedures table Overhead track mounted or C arm x ray unit with fluoroscopy e X ray generator location X ray control console Remote afterloader control console e In room radiation detector e In room and remote radiation indicators e Remote afterloader storage and treatment locations e Operating room procedures light e Storage applicators and medical supplies e Door interlock e Treatment applicators Applicator positioning clamp Integral with procedures table Emergency off buttons at console in maze and in room e Emergency lighting Wall or ceiling mounted Emergency power for selected equipment Audio video anesthesia patient monitoring lighting radiation detectors and indicators remote afterloader Optional dedicated scrub area Optional halon fire protection Halon reservoir and discharge head s Optional treatment planning workstation 27 Dedicated Remote Afterloading and Minor Procedures Suite optional Designed for 10 Curies of Iridium 192 scrub area 147 Ib f
104. ters for a planned therapy entry errors can occur Often with high dose rate units operators must treat a waiting patient as soon as possible due to the patient s medical condition and the pressure to treat quickly can contribute to user generated errors Procedures should exist to allow quick but independent confirmation by a second person of two aspects of the proposed treatment The planned treatment parameters and the entry into the operating console of the planned treatment parameters Errors can occur in both 18 19 processes Preparation and use of well planned pre treatment forms and check lists for each anatomic site commonly treated is recommended A generic checklist could include but would not be limited to the following items Have the pre treatment functional QA tests been done Is the prescription written directive completed and signed Has the prepared treatment plan prescription target volume specification dose dose rates number of sources their spatial 61 positions etc been independently reviewed e g will the planned use of the device yield the desired dose and dose distribution Have the treatment parameters keyed by an operator into the microprocessor controlling the unit been reviewed by a second individual Are all pre treatment forms completed and signed prior to treatment Do pre treatment autoradiographs if any confirm the proposed treatment is correctly entered into the console Stand
105. the tested radionuclides are contained in other than a standard container For example assays of Cs sealed sources using a Cs calibration point will not be absolutely accurate because of the difference in features of the calibration ampule of Cs and the sealed source Calibrations of either long or short lived low activity brachytherapy sources by well ionization chambers designed for these sources is described in AAPM Report 13 and in other articles Most 63 recently Weaver et al reviewed chamber calibration energy dependence position dependence and response stability of well ionization chambers designed for calibration of LDR sources The LDR sources in remote afterloading units can also be calibrated in these well ionization chambers per AAPM Report 13 assuming that the well ionization chamber is calibrated for the LDR radioisotope Co Cs or Ir The AAPM Task Group 40 report reviews the quality assurance tests for brachytherapy source calibrators Well ionization chambers designed to accommodate the large currents associated with HDR sources are now available Goetsch et al report a design of a re entrant well type ionization chamber for use with Ir HDR sources the chamber accommodates a 10 nA current from a 370 GBq 10 0 Ci Ir source The chamber is calibrated for Ir HDR sources of specific design and encapsulation The University of Wisconsin ADCL and K amp S Associates Inc ADCL provide ca
106. the unit contains multiple sources of the same nominal activity one needs to determine the average activity and standard deviation of the lot and confirm that they meet manufacturer stated certificate values Methods of absolute calibration are discussed in Section VIII of the report E Brachytherapy Planning Computer For any computer system that produces isodose curves for remote afterloaders it is imperative that the user understand the algorithm and exactly how the doses are computed The user may have to enter key parameters specific to a radionuclide and source model or select parameters from an existing menu Source activities may be expressed in megabecquerels millicuries apparent millicuries milligram radium equivalents alternately the certificate may state the reference air kerma rate at l m or air kerma strength produced by the source AAPM Report 21 Specification of Brachytherapy Source Strength is a valuable guide to understanding these parameters Modifying effects of the source capsule on the dose distribution may be considered or neglected depending on the ability of the computational algorithm to represent those effects the same is true of the modification caused by source carriers or applicators Tissue attenuation and multiple scattering corrections must also be considered It is beyond the scope of this document to discuss all of these topics for the many radioisotopes source models and applicator systems avail
107. the user has purchased suitable LDR and HDR sources The Curietron has four channels and is available as a low medium or high dose rate unit The source safe contains Cs sources 1 8 mm in external diameter by 5 3 mm in length and inactive spacers that arc loaded to form sources of the desired active lengths The device contains the storage safe for the sources the electromechanical transfer system and the operating control panel Sources with activities varying from 555 MBq 15 0 mCi to 5 55 GBq 150 mCi with active length of 8 mm to 96 mm can be formed Conventional metallic applicators of either the Fletcher or Henschke design are available as are plastic applicators of the DeLouche or Chassagne type popular in Europe The high dose rate projector can contain up to 185 GBq 5 0 Ci of CS Table 1 a Low Medium and High Dose Rate Remote Afterioading Devices Manufacturer or Vendor Outside Diameter 10 11 12 13 14 Modality of Applicators Method of Source Transfer Method of Source Movement Method of Source Retraction in the Event of a Failure Storage of Source Simulation Sources for Treatment Simulation Applicators Abdilable Accuracy of Source Position Source Arrangements and Dose Calculation Uses Conventional RTP Software or Dosimetry Dose Optimiza tion Table Bladder and Rectal Dosimetry Afterloading BUCHLER Buchler GmbH Germany Low Medium High I
108. titute of Standards and Technology primary standards and for re entrant well ionization chambers used as tertiary standards we still lack a NIST primary standard for thimble ionization chambers irradiated with Ir Moreover participants of a recent NIST workshop The Calibration of Iridium 192 Sources for Use in High Dose Rate HDR Brachytherapy indicated development of a primary standard is unlikely in the immediate future The Task Group 41 final report does explain the recently adopted AAPM approved ADCL procedure for obtaining an N factor for Ir for thimble chambers by interpolation between other N factors for energies bounding Ir explains how this factor is transferred to re entrant well ionization chambers and advises AAPM members on the use of re entrant well ionization chambers for measuring source activity Finally significant developments in methods of Ir source calibrations that may have occured while this manuscript was in press obviously are excluded Nevertheless we trust this report will serve as a useful resource for the members of the American Association of Physicists in Medicine and others Glenn P Glasgow Chairman TG 41 March 2 1993 iii ACKNOWLEDGEMENTS We appreciate contributions to Tables 1 and 2 from K Herold for Buchler J Moe for ORIS M Mount for Nucletron F Mick for Gamma Med and R Calfee for Omnitron Their contributions comments and suggestions were appreciated We appreciate the
109. trom Effect of Source Encapsulation in the Energy Spectra of Ir 192 and Cs 137 Seed Sources Phys Med Biol 36 495 505 1991 P R Almond J R Marbach P M Stafford Brachytherapy Buildup Factors for Cesium 137 Rays Endocurietherapy Hyperthermia Oncology 5 49 52 1989 P W Grigsby J F Williamson C A Perez Source Configurations and Dose Rates For The Selectron Afterloading Equipment For Gynecologic Applicators Int J Radiat Oncol Biol Phys 24 321 327 1992 C Pla M D Evans E B Podgorsak Dose Distribution Around Selectron Applicators Int J Radiat Oncol Biol Phys 13 1761 1766 1987 106 100 101 102 103 J A Meli L L Anderson K A Weaver Dose Distribution in Interstitial Brachytherapy Interstitial Collaborative Working Group Raven Press New York 1990 21 31 H C Park and P R Almond Evaluation of the Build up Effect of an Ir High Dose Rate Brachytherapy Source Med Phys 19 1293 1297 1992 J A Meli A S Meigooni R Nath On the Choice of Phantom Material for Ir Sources Int J Radiat Oncol Biol Phys 14 587 593 1988 L L Anderson Remote Afterloading in Cancer Management Part I Afterloader Design and Optimization Potential in Brachytherapy Oncology 1983 edited by B S Hilaris M A Batata Memorial Sloan Kettering Cancer Center New York 1983 93 100 107
110. ttery Emergency battery to operate air reservoir for pneumatic retum 15 in unit 45 in mobile safe Allin unit Manual Manual or 1 mCi Co source available option Interstitial applicators either rigid or flexible bronchial esophageal gt 60 types l mm pneumatic check i mm with penumatic check Linear or point interstitial sources arranged by user Point sources individually constructed to yield any desired distribution Yes or uses A Yes has dedicated dedicated IBM PC IBM PC and software however conventional RTP point source pro grams could De used Visual inspection of isodose distribution Measured doses using pilot sources Table 1 2 Cont d Low Medium and High Dose Rate Remote Afterinading Devices Manufacturer or Vendor 1 Dose Rates 2 Modality 15 Source Container Maximum Storage Act ity 16 Special Features 17 Number of Applicator Channels IR Ma ximum Number of Sources in Projector 19 Ma ximum Number of Channets Used Simultaneously SOURCES Radioisotope Physical Size Afterloading BUCHLER Buchler GmbH Gennany Low Medium High Intracavitary intraluminal interstitial Cs 12 Ci Co 1 2 Ci ir ici Options for interchange between LDR amp HDR modes Jor3 1 oscillating 2 stationary AVAILABLE Cs Capsule 11 5 mm L x 6 5 mm OD Cs Ci HDR Curietron Oris CIS US France Tow
111. urce strength at the time of source change or alternately measuring the new old strength ratio in a well chamber prior to the in air measurement of the new source strength 4 The dose to a medium from the in air calibration The dose rate to a small mass of water in free space at r where the radius of the water sphere is the minimum required to establish either charged particle equilibrium or transient charged particle equilibrium is D tre alt X t W ae Heal PNE Aca Banter Gy s 19 Hen P the ratio of mass energy absorption coefficients where Ag the equilibrium thickness attenuation correction for the small mass of water in free space Boosie the quotient of absorbed dose by collisional air kerma rate Attix provides an excellent discussion with numerical examples of Heal PYE Aggy and Byer for ratio and Cs Table 5 includes these values as well as values for Ir as selected by TG 41 The dose rate at a point r 6 in a full scattering phantom is Dawa ts Doo palT F 1 9 Gy s 20 87 Table 5 Values of Bua Acq and 4 p i for Ir Cs and Co 1927r BIC Co Ponor 1 000 1 001 1 003 Ag 1 000 0 996 0 988 Bal 1 112 1 114 1 111 Note Aa i Boaa P water s Pt vater 7Cs and Co data after F H Attix Introduction to Radiological Physics and Radiation Dosimetry John Wiley amp Sons New York 1986 p 364 where the anisotropy factor F r is the
112. ver requirements the regulatory agency has established for those allowed to exchange sources Generally this issue must be addressed in the license application Proper documentation of the contents of this training and attendance records of those who attend arc generally required by regulatory agencies Generally the license will have been written to identify the individual physicist safety officer or others who are then responsible for instructing the nursing staff or other staff members who become involved in operating the unit The identified individual usually the radiologic physicist or health physicist is responsible for providing instruction on radiation safety procedures to all personnel caring for patients treated with the remote afterloader including retraining at the intervals specified in the license VI ACCEPTANCE TESTING The acceptance tests establish the baseline operating performance parameters of the remote afterloading device and facility They can be broadly divided into 1 the mechanical and electrical operation of the remote afterloading device and radiation monitors 2 the mechanical and electrical features of the facility 3 the integrity of the applicators 4 the integrity and proper operation of the radioactive source s and 5 the proper operation of the computer that generates isodose distributions Numerous authors have reported acceptance tests and quality assurance procedures for remote afterloaders
113. y storage of 100 allows use of small channels and memory interstitial needies card 10 18 1 1 1 1 mir mir Capeute 0 59 mm OD 25mm capoule engh x 10mm L 1 1 mm diameter 12 Ci max 0 5 to 1 Ci Table 2 a High Dose Rate Remote Aftericading Devices 10 11 Outside Diameter of Applicators Method of Source Transfer Method of Source Movement Method of Source Retraction in the Event of Failure Storage of Source Simulation Sources for Treatment Simulation Applicators Available Accuracy of Source Position Source Arrangements and Dose Calculations Ahecloading Nocietroe BUCHLER Facts i Engineering Buchler GmbH amp Ce BV Atracavitary Intraluminal Interstitial Interstitial Intracavitary S mm to 1 7 mm Cs 4 2 to 3 2 mm Sources welded to Sources auto connect Source laser welded steel drive cable to drive cable Steel drive cables to drive cable Stepping motor None static Shifting mechanism Stepping motor 60 steps to 32 steps over 48 stepe of 25 mm 300 mm length 640 mm over 12 cm length 5 mm over 24 cm 48 steps Emergency motor Backup battery and Backup battery Dual monitors and backup battery safety device backup battery emergency hand crank 10 or 20 preloaded 4G trains in mobile safe No Dummy Source All applicators on the Delouche Chassagne Same as Curietron Flexible and rigid market are usable Fletcher Henschke plus int

remote afterloading technology - The American Association of

Contents

Download Pdf Manuals

Related Search

Related Contents