Room: AAPM ePoster Library
Purpose: plaque dose evaluations traditionally follow the TG43 formalism, however, ocular doses are in error by up to 90%, motivating adoption of advanced algorithms and production of reference datasets. Towards these goals, this work updates and extends the Carleton Laboratory for Radiotherapy Physics (CLRP) database for eye plaque (EP) brachytherapy with photon-emitting sources using the EGSnrc-application egs_brachy.
Methods: simulated include 10-24 mm diameter Collaborative Ocular Melanoma Study (COMS), 12-20 mm BEBIG-COMS, and 4 other representative published models. Brachytherapy seeds for 125I (model 6711, IsoSeeds I25.S06/16), 103Pd (model 200), and 131Cs (Isoray) are considered. Doses are calculated with egs_brachy in water phantoms containing (0.05cm)3 voxels spanning the eye for 2 scenarios: (i) ‘HOMO’: seeds in water with no plaque or interseed effects (TG43-simulated conditions); (ii) ‘HETERO’: seeds fully modelled in eye plaques. For validation, dose distributions are compared to the previous database (CLRP_EPv1; only 10-22 mm 103Pd/125I COMS plaques modelled with BrachyDose) and other publications.
Results: 3D dose distributions are in good agreement with previous results. For example, for the COMS 16 mm plaques loaded with 103Pd seeds, doses along the central EP axis (and 8 points of interest) are within 1.4% (0.8%) with CLRP_EPv1, and within 5% (11.7%) with published MCNP calculations; the corresponding results for 125I are 0.5% (1.7%), and 4% (19.5%), respectively. The 125I BEBIG-COMS 16 mm plaques (simulated for the first time) have doses that differ by 3% (sclera) and 15% (opposite side of the eye) relative to standard COMS, due to differences in density/composition and seed model. For all plaques, significant dose reductions for HETERO relative to HOMO scenarios are observed.
Conclusion: 3D dose distributions and benchmarked eye plaque models for use in egs_brachy have been successfully produced, and will be freely distributed, enabling advances in ocular brachytherapy research and clinical practice.
Funding Support, Disclosures, and Conflict of Interest: funding sources from Natural Sciences and Engineering Research Council (NSERC) of Canada, Canada Research Chairs, Ontario Ministry of Research and Innovation. Disclosures and Conflict of Interest: Some of this work was supported by Eckert & Ziegler BEBIG.