- Purpose and Rationale
Many individual users contact the AAPM Brachytherapy Subcommittee (BTSC) and IROC Houston asking which of the available photon-emitting brachytherapy source models conform to the AAPM's guidelines. The AAPM guidelines are based on reports for low-energy and high-energy photon-emitting brachytherapy sources:
- R. Nath, L. L. Anderson, G. Luxton, K. A. Weaver, J. F. Williamson, and A. S. Meigooni, "Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM Radiation Therapy Committee Task Group No. 43," Med. Phys. 22, 209-234 (1995).
- R. Nath, L. L. Anderson, J. A. Meli, A. J. Olch, J. A. Stitt, and J. F. Williamson, "Code of practice for brachytherapy physics: Report of the AAPM Radiation Therapy Committee Task Group No. 56," Med. Phys. 24, 1557-1598 (1997).
- H. D. Kubo, G. P. Glasgow, T. D. Pethel, B. R. Thomadsen, and J. F. Williamson, "High dose rate brachytherapy treatment delivery: Report of the AAPM Radiation Therapy Committee Task Group No. 59," Med. Phys. 25, 375-403 (1998).
- J. F. Williamson, B. M. Coursey, L. A. DeWerd, W. F. Hanson, R. Nath, and G. Ibbott, ''Guidance to users of Nycomed Amersham and North American Scientific, Inc. I-125 Interstitial Sources: Dosimetry and calibration changes: Recommendation of the American Association of Physicists in Medicine Radiation Therapy Committee Ad Hoc Subcommittee on Low-Energy Seed Dosimetry,'' Med. Phys. 26, 570-573 (1999).
- J. F. Williamson, B. M. Coursey, L. A. DeWerd, W. F. Hanson, R. Nath, M. J. Rivard, and G. Ibbott, ''On the use of apparent activity (Aapp) for treatment planning of 125I and 103Pd interstitial brachytherapy sources: Recommendations of the American Association of Physicists in Medicine Radiation Therapy Committee Subcommittee on Low-Energy Brachytherapy Source Dosimetry,'' Med. Phys. 26, 2529-2530 (1999).
- M. J. Rivard, B. M. Coursey, L. A. DeWerd, W. F. Hanson, M. S. Huq, G. S. Ibbott, M. G. Mitch, R. Nath, and J. F. Williamson, "Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations," Med. Phys. 31, 633-674 (2004).
- L. A. DeWerd, M. S. Huq, I. J. Das, G. S. Ibbott, W. F. Hanson, T. W. Slowey, J. F. Williamson, and B. M. Coursey, "Procedures for establishing and maintaining consistent air-kerma strength standards for low-energy, photon-emitting brachytherapy sources: Recommendations of the Calibration Laboratory Accreditation Subcommittee of the American Association of Physicists in Medicine," Med. Phys. 31, 675-681 (2004).
- Z. Li, R.K. Das, L. A. DeWerd, G. S. Ibbott, A. S. Meigooni, J. Perez-Calatayud, M. J. Rivard, R. S. Sloboda and J. F. Williamson, "Dosimetric prerequisites for routine clinical use of photon emitting brachytherapy sources with average energy higher than 50 keV," Med. Phys. 34, 37-40 (2007).
- M. J. Rivard, W. M. Butler, L. A. DeWerd, M. S. Huq, G. S. Ibbott, A. S. Meigooni, C. S. Melhus, M. G. Mitch, R. Nath, and J. F. Williamson, "Supplement to the 2004 update of the AAPM Task Group No. 43 Report," Med. Phys. 34, 2187-2205 (2007).
- W. M. Butler, W. S. Bice Jr., L. A. DeWerd, J. M. Hevezi, M. S. Huq, G. S. Ibbott, J. R. Palta, M. J. Rivard, J. P. Seuntjens, and B. R. Thomadsen, "Third-party brachytherapy source calibrations and physicist responsibilities: Report of the AAPM Low Energy Brachytherapy Source Calibration Working Group," Med. Phys. 35, 3860-3865 (2008).
The Radiation Therapy Oncology Group (RTOG) has asked IROC Houston to identify those brachytherapy sources that meet the AAPM dosimetric prerequisites, since participating institutions will be expected to use sources meeting these prerequisites. This joint AAPM/IROC Houston is intended to satisfy the RTOG request and similar requests that have arisen from other cooperative clinical trial study groups.
The AAPM and IROC Houston work together to identify and register brachytherapy sources that meet the AAPM criteria. A webpage-based Registry is maintained by IROC Houston, listing sources that meet the AAPM criteria. IROC Houston relies on the AAPM's BTSC, through its Brachytherapy Source Registry Work Group (WGBSR), to establish the criteria for including or excluding source models from this Registry, and to determine which source models meet the criteria. As the recommendations are intended to apply internationally, some of the agencies, organizations and standard laboratories identified within the U.S. could be, at the discretion of the BTSC, interpreted in the context of the arrangements in other countries where applicable.
- Compliance Registry Appearance and Contents
The Registry is in the form of a webpage reachable via hot links from both the AAPM and IROC Houston websites, and is entitled "Joint AAPM/IROC Houston Registry of Brachytherapy Sources Meeting the AAPM Dosimetric Prerequisites." The webpage displays the following information for each source model listed on the Registry: The vendor (manufacturer if different), radionuclide, model number, trade name, date of addition to the Registry, and dosimetry publications taken as evidence of compliance.
Links to this Policy, the AAPM prerequisites publications, other publications subsequently determined to be relevant, as well as an application form to be used by source vendors are kept accessible on the webpage.
The following text appears verbatim on the webpage:
The AAPM, through its Brachytherapy Subcommittee, has determined that the following brachytherapy source models comply with the AAPM's dosimetric prerequisites as set forth in one of two publications: "Dosimetric prerequisites for routine clinical use of new low-energy photon interstitial brachytherapy sources: Recommendations of the American Association of Physicists in Medicine Radiation Therapy Committee". Med. Phys. 25, 2269-2270 (1998), or "Dosimetric prerequisites for routine clinical use of photon emitting brachytherapy sources with average energy higher than 50 keV," Med. Phys. 34, 37-40 (2007). The manufacturers must also satisfy criteria established by the AAPM Subcommittee on Calibration Laboratory Accreditation and described in a publication (hereafter referred to as "the 2004 CLA Report"): "Procedures for establishing and maintaining consistent air-kerma strength standards for low-energy, photon-emitting brachytherapy sources: Recommendations of the Calibration Laboratory Accreditation Subcommittee of the American Association of Physicists in Medicine". Med. Phys., 35 671-685 (2004). The criteria are summarized here:
The AAPM dosimetric prerequisites for brachytherapy sources may be summarized as follows The vendor provides air-kerma strength calibrations that are directly or indirectly traceable to the air-kerma strength standards (SK,N99 for low energy sources) for photon emitting brachytherapy sources maintained by NIST, or in the case of HDR 192Ir, the standard developed by the University of Wisconsin and maintained by the ADCLs.
- A full set of TG-43 dosimetric parameters is available, supporting both calculation of the 2-D dose-rate distribution and, for low-energy seed models, the 1-D isotropic point source approximation. This set of dosimetric parameters must be based upon at least one experimental study and at least one Monte Carlo study of the source model's dosimetric parameters. These studies must be performed by investigators having independence from the manufacturer, and have been accepted for publication in a peer-reviewed journal.
- The vendor has assured that the calibration from NIST has been transferred to the ADCLs.
- The vendor has implemented a program that is compliant with the 2004 CLA Report for periodically comparing its air-kerma strength calibrations with the NIST primary standard and the secondary standards maintained by the ADCLs.
The complete text of the 2004 CLA report is available here.
The AAPM dosimetric prerequisites for high-energy sources may be summarized as follows:
- The single-source dose distribution used for clinical treatment planning should be based upon two dose-rate determinations, one of which is a theoretical calculation method such as the Monte Carlo method, and the other an experimental measurement. Note that a single dosimetric study is acceptable for certain 137Cs, 192Ir, and 60Co sources under specific circumstances (see the complete text.)
- A full set of TG-43 dosimetric parameters is available, supporting calculation of the 2-D dose-rate distribution. In addition, a set of "along and away" tables must be provided.
- The vendor provides air-kerma strength calibrations that are directly or indirectly traceable to the air-kerma strength standards for photon emitting brachytherapy sources maintained by NIST.
- The vendor has implemented a program of periodically comparing its air-kerma strength calibrations with the NIST primary standard or the secondary standards maintained by the ADCLs that is compliant with the CLA Report. Note, however, that while the CLA Report specifically addresses low-energy sources, the AAPM has confirmed that manufacturers are expected to comply with its requirements for high-energy sources also. The CLA Report was dedicated to low-energy sources. Until a similar report is available for high-energy sources, vendors must apply these guidelines with appropriate variations. For example, it may be necessary to send a source or a measurement system to NIST or an ADCL.
- In addition, the AAPM requires biennial comparisons for high-energy sources through Measurement Quality Assurance (MQA) tests.
- In the case of experimental sources for which no ADCL interpolative or NIST primary standard exists, the end user institution is responsible for calibrating the sources with an ionization chamber of appropriate dimensions that has calibrations directly traceable to an appropriate NIST air-kerma standard.
The webpage will contain the following disclaimer:
The AAPM and IROC Houston maintain this Registry solely as a service to their members and clients. Neither the AAPM nor IROC Houston endorses or approves specific products. No statement regarding the quality of construction, safety, or clinical effectiveness of specific sources is expressed or implied by inclusion or exclusion of sources from this Registry. The AAPM Brachytherapy Subcommittee bases its decisions to place or exclude source models in this Registry on the content of published papers and the vendor's descriptions of its calibration procedure. The AAPM and IROC Houston neither warrant nor are responsible for (a) accuracy of the published dosimetry studies and applicability to the sources as manufactured; (b) compliance of the vendor with its stated procedures; or (c) the accuracy of any particular brachytherapy source calibration. The AAPM does not monitor on a continuing basis the compliance of the vendor's calibration procedures with the AAPM prerequisites nor the compatibility of its source design and manufacturing practices with the published dosimetry data.
- Procedures for Registry Inclusion
- Request for inclusion of a source model is initiated by the vendor applying to the AAPM BTSC for this purpose.
- A special case exists for orphaned sources; those no longer commercially available, but still in regular use in hospitals. These must be sources with long half-life and suitable dose rates which consequently comprise only certain models of 137Cs and 60Co sources. In the case of these sources, there is no manufacturer available to submit the Registry application forms. For these orphaned sources, the AAPM and IROC Houston have agreed to an alternative procedure for Registry application: a hospital that wishes to participate in a clinical trial that involves brachytherapy sources not currently posted on the Registry may submit the application, listing the dosimetric studies available and the dosimetry parameters to be used for treatment planning. The hospital must also describe their method of source strength traceability for review by the IROC Houston to assure the correct calibration of the sources. In the special case of source trains, in which individual sources cannot be removed for calibration with a well chamber, the hospital may describe a method of calibration at a distance in a phantom, in accordance with calibration procedures described in the peer-reviewed literature.
- Upon receipt, BTSC will deliver the application to WGBSR, which will review the published/accepted dosimetry papers. WGBSR will review the vendor's statements regarding calibration procedures with appropriate NIST Group Leader as well as the ADCL Directors and the AAPM CLA Subcommittee chair. WGBSR may withhold entry into the Registry until any discrepancies between the vendor's statements and calibration lab personnel observations are resolved satisfactorily. Following its review, WGBSR will forward a recommendation for or against inclusion in the Registry to BTSC.
- BTSC has adopted the following "Independence Policy" (reproduced from "Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations." Med. Phys. 31, 633-674 (2004):
The first meaning of "independent studies" is that they are performed, written, and published by investigators who are affiliated with institutions independent of the source vendor and who have no major conflicts-of interest with that vendor.
The second meaning of "independent studies" is that they are scientifically independent of one another, i.e., they represent independent and distinct estimations of the same quantities. In the case of two measurement based studies, this will usually mean that two different investigators have used their own methodologies for measuring and sampling the relative dose distribution, as TLD dosimetry is highly technique and investigator dependent. In the case of an empirical study and a Monte Carlo study, if properly executed, they will yield scientifically independent estimates of the TG-43 parameters. Thus, so long as the two studies are successfully scrutinized by the peer-review process and satisfy the AAPM scientific requirements, the empirical and Monte Carlo investigator author lists can overlap or even be identical. It is permissible to publish the Monte Carlo and measured estimates in the same paper so long as the two datasets are independently tabulated. In this context, "Not independent" means that the one study is used to modify the outcomes and methods of the other to improve agreement between the two datasets in a manner that is not scientifically justified.
- BTSC has adopted the following "Data Overlap Policy": We require that, for sources other than conventionally-encapsulated 137Cs, 192Ir, and 60Co sources. two dosimetry studies each assess: (a)Λ ; (b) gL(r) or gP(r); (c) F(r,θ) and φan(r) with r and sampling resolution at least as good as that recommended in the 2004 AAPM TG-43U1 (low-energy) and Li et al. 2007 (high-energy) reports so that overlap between the two studies may readily reveal significant discrepancies if present; and (d) L or Leff. As provided in reference (8) above, a single dosimetry study is acceptable for conventionally-encapsulated 137Cs 192Ir, and 60Co sources.
- BTSC expects that vendors will comply with the AAPM prerequisite requiring periodic comparisons of their calibrations with those of an independent laboratory. Vendors can best do this by participating in comparisons with both NIST and the ADCLs offering calibration services for that source model. The AAPM has recommended a procedure and a frequency for such comparisons in: "Procedures for establishing and maintaining consistent air-kerma strength standards for low-energy, photon-emitting brachytherapy sources: Recommendations of the Calibration Laboratory Accreditation Subcommittee of the American Association of Physicists in Medicine." Med. Phys. 31, 675-681 (2004). The AAPM High Energy Brachytherapy Source Dosimetry working group (HEBD) has set a calibration comparison frequency of two years for 60Co, 137Cs, and 192Ir. Vendors of these high-energy sources should comply with this comparison frequency.
- Inclusion into the Registry is by majority vote of the BTSC. Written notification of any unfavorable decision will be provided to the vendor by the WGBSR chair along with an explanation.
- Upon completion of a positive vote for inclusion by the BTSC, IROC Houston will be informed of the decision and instructed to add the source model to the Registry.
- BTSC reserves the right to withhold entry into the Registry if it believes that the dosimetry articles contain technical errors or omissions; or rely on unproven or inappropriate computational or experimental dosimetry methodologies.
- Upon receipt of notification of rejection of a source from the Registry, a manufacturer may appeal the decision by submitting a written request for review to the AAPM Therapy Physics Committee (TPC). The TPC will assign a minimum of three physicists to review the materials submitted to the BTSC and the decision made by BTSC. TPC may decide to endorse or reverse the decision of the BTSC.
- This Policy may be revised as new source models or technologies emerge.
- Procedures for Registry Removal
Vendors (or hospitals according to section C.2) may request that a source be removed from the Registry on the grounds that it will no longer be available to the medical community. Immediate steps will be taken to remove the source from the Registry upon receipt of a specific written request from the manufacturer, source distributor, or hospital.
While manufacturers are encouraged to contact the BTSC should there be any changes in their source manufacturing processes, the BTSC retains the discretion to remove a product from the Joint AAPM/IROC Houston Registry should it have grounds to believe that a product, as currently manufactured, is no longer accurately characterized by the reference-quality dose-distribution data submitted in support of Registry posting. Reasonable grounds include, but are not limited to: change of manufacturing venue or process, changes in source geometry and/or internal design, and discovery of deficiencies in the published dosimetry data.
To retain Registry status, the vendor may submit for BTSC review a set of revised dosimetry data that meet the standards specified by the AAPM dosimetric prerequisites. Alternatively, the vendor may provide evidence to BTSC demonstrating that the revised product is dosimetrically equivalent to the original source from which the published and accepted dosimetry data were derived. Such information should include, as applicable,
- Assurances from the vendor that manufacturing processes are unchanged and the geometric and compositional structure of relevant source components are unchanged.
- Review of quality assurance data (e.g., source radiograph, optical micrographs, measurements, etc.) and vendor manufacturing processes with original dosimetry investigators. These investigators must make a recommendation regarding equivalence to BTSC and be willing to discuss findings with BTSC in closed session.
- Review of NIST anisotropy and spectroscopy measurements before and after the product change.
- A description of the vendor's efforts and checks, along with their outcome, to assure the equivalence of their current product with that at the time of original dosimetric characterization.
The above information should be submitted to BTSC with sufficient lead-time that BTSC can make a recommendation prior to the vendor distributing the modified product commercially for routine clinical use.
Failure of a vendor to maintain a regular program of comparisons with NIST and an ADCL, in accordance with the recommendations of the AAPM Calibration Laboratory Accreditation (CLA) Subcommittee (Med. Phys. 31, 675-681 (2004) or Med. Phys. 34, 37-40 (2007)) may result in removal. When CLA determines that a vendor has exceeded the recommended interval, the CLA chair will issue a warning. If a response to the chair's communication is not received within 60 calendar days, the CLA chair will notify the BTSC chair that the source model should be removed from the Registry. The decision to remove a source model from the Registry will be made by majority vote of the BTSC. Upon completion of a vote to remove, IROC Houston will be instructed to remove the source from the webpage Registry.
The following application is available for download from the Registry webpage.
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