Dosimetry of eye plaques for ocular tumors presents unique challenges in brachytherapy. The challenges in accurate dosimetry are in part related to the steep dose gradient in the tumor and critical structures that are within millimeters of radioactive sources. In most clinical applications, calculations of dose distributions around eye plaques assume a homogenous water medium and full scatter conditions. Recent Monte Carlo (MC)-based eye-plaque dosimetry simulations have demonstrated that the perturbation effects of heterogeneous materials in eye plaques, including the gold-alloy backing and Silastic insert, can be calculated with reasonable accuracy. Even additional levels of complexity introduced through the use of gold foil "seed-guides" and custom-designed plaques can be calculated accurately using modern MC techniques. Simulations accounting for the aforementioned complexities indicate dose discrepancies exceeding a factor of ten to selected critical structures compared to conventional dose calculations. Task Group 129 was formed to review the literature; re-examine the current dosimetry calculation formalism; and make recommendations for eye-plaque dosimetry, including evaluation of brachytherapy source dosimetry parameters and heterogeneity correction factors. A literature review identified modern assessments of dose calculations for Collaborative Ocular Melanoma Study (COMS) design plaques, including MC analyses and an intercomparison of treatment planning systems (TPS) detailing differences between homogeneous and heterogeneous plaque calculations using the American Association of Physicists in Medicine (AAPM) TG-43U1 brachytherapy dosimetry formalism and MC techniques. This review identified that a commonly used prescription dose of 85 Gy at 5 mm depth in homogeneous medium delivers about 75 Gy and 69 Gy at the same 5 mm depth for specific (125)I and (103)Pd sources, respectively, when accounting for COMS plaque heterogeneities. Thus, the adoption of heterogeneous dose calculation methods in clinical practice would result in dose differences >10% and warrant a careful evaluation of the corresponding changes in prescription doses. Doses to normal ocular structures vary with choice of radionuclide, plaque location, and prescription depth, such that further dosimetric evaluations of the adoption of MC-based dosimetry methods are needed. The AAPM and American Brachytherapy Society (ABS) recommend that clinical medical physicists should make concurrent estimates of heterogeneity-corrected delivered dose using the information in this report's tables to prepare for brachytherapy TPS that can account for material heterogeneities and for a transition to heterogeneity-corrected prescriptive goals. It is recommended that brachytherapy TPS vendors include material heterogeneity corrections in their systems and take steps to integrate planned plaque localization and image guidance. In the interim, before the availability of commercial MC-based brachytherapy TPS, it is recommended that clinical medical physicists use...

Since publication of the 2004 update to the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (TG-43U1), several new low-energy photon-emitting brachytherapy sources have become available. Many of these sources have satisfied the AAPM prerequisites for routine clinical use as of January 10, 2005, and are posted on the Joint AAPM/RPC Brachytherapy Seed Registry. Consequently, the AAPM has prepared this supplement to the 2004 AAPM TG-43 update. This paper presents the AAPM-approved consensus datasets for these sources, and includes the following 125I sources: Amersham model 6733, Draximage model LS-1, Implant Sciences model 3500, IBt model 1251L, IsoAid model IAI-125A, Mentor model SL-125/ SH-125, and SourceTech Medical model STM1251. The Best Medical model 2335 103Pd source is also included. While the methodology used to determine these data sets is identical to that published in the AAPM TG-43U1 report, additional information and discussion are presented here on some questions that arose since the publication of the TG-43U1 report. Specifically, details of interpolation and extrapolation methods are described further, new methodologies are recommended, and example calculations are provided. Despite these changes, additions, and clarifications, the overall methodology, the procedures for developing consensus data sets, and the dose calculation formalism largely remain the same as in the TG-43U1 report. Thus, the AAPM recommends that the consensus data sets and resultant source-specific dose-rate distributions included in this supplement be adopted by all end users for clinical treatment planning of low-energy photon-emitting brachytherapy sources. Adoption of these recommendations may result in changes to patient dose calculations, and these changes should be carefully evaluated and reviewed with the radiation oncologist prior to implementation of the current protocol.

Monte Carlo (MC) simulations were performed to estimate brachytherapy dose distributions for Collaborative Ocular Melanoma Study (COMS) eye plaques. Brachytherapy seed models 200, 6711, and CS-1 Rev2 carrying 103Pd, 125I, and 131Cs radionuclides, respectively, were modeled and benchmarked against previously published values. Calculated dose rate constants MClambda were 0.684, 0.924, and 1.052 cGy h(-1) U(-1) (+/- 2.6%, k = 1 uncertainty) for models 200, 6711, and CS-1 Rev2, respectively. The seeds were distributed into 10, 12, 14, 16, 18, 20, and 22 mm-diameter COMS eye plaques. Simulations were performed in both heterogeneous and homogeneous environments, where the latter were in-water and the former included the silastic seed carrier insert and gold-alloy plaque. MC-based homogenous central axis dose distributions agreed within 2% +/- 1% (+/- 1 s.d.) to hand-calculated values. For heterogeneous simulations, notable photon attenuation was observed, with dose reduction at 5 mm of 19%, 11%, and 9% for 103Pd, 125I, and 131Cs, respectively. A depth-dependent correction factor was derived to correct homogenous central-axis dose distributions for plaque component heterogeneities, which were found to be significant at short radial distances.

Agreement within 2% was observed among conventional brachytherapy TPS and MC codes for intraocular brachytherapy dose calculations in a homogeneous water environment. In general, the magnitude of dose errors incurred by ignoring the effect of the plaque backing and Silastic insert (i.e., by using the TG-43 approach) increased with distance from the plaque's central-axis. Considering the presence of material heterogeneities in a typical eye plaque, the best method in this study for dose calculations is a verified MC simulation.

Cs (IsoRay Medical model CS-1 Rev2). Observations are included on the behavior of these dosimetry parameters as a function of radionuclide. Recommendations are presented on the selection of dosimetry parameters, such as from societal reports issuing consensus datasets (e.g., TG-43U1, AAPM Report #229), the joint AAPM/IROC Houston Registry, the GEC-ESTRO website, the Carleton University website, and those included in software releases from vendors of treatment planning systems. Aspects such as timeliness, maintenance, and rigor of these resources are discussed.Links to reference data are provided for radionuclides (radiation spectra and half-lives) and dose scoring materials (compositions and mass densities). The recent literature is examined on photon energy response corrections for thermoluminescent dosimetry of low-energy photon-emitting brachytherapy sources. Depending upon the dosimetry parameters currently used by individual physicists, use of these recommended consensus datasets may result in changes to patient dose calculations. These changes must be carefully evaluated and reviewed with the radiation oncologist prior to their implementation.