Purpose: To evaluate the dosimetry of brachytherapy treatments for intraocular tumours by comparing results from several Monte Carlo (MC) systems and one commercial model-based dose calculation algorithm (MBDCA). This work is done in order to develop test cases for adopters of MBDCAs. The scenario investigated here is the treatment of ocular melanoma using a Collaborative Ocular Melanoma Study (COMS) 16 mm eye plaque loaded with 13 model 6711 ¹²⁵I seeds.
Methods: The levels of agreement among four MC codes (EGSnrc egs_brachy, Geant4 ALGEBRA, Penelope2014, and MCNP6) were evaluated by comparing the results from various test cases. Some comparisons were also done using a research version of the OncentraBrachy/ACE commercial TPS. The test cases included: i) modelling the 13 seeds individually, ii) combined in water positioned within the plaque, iii) the full COMS plaque in a water phantom, and iv) the full plaque in a realistic eye phantom. Local and global dose comparisons were made.
Results: For all test cases, local agreement of ALGEBRA, MCNP, and Penelope with egs_brachy was within 2% and global agreement was within 1%. These values are consistent with the typical uncertainties expected in the low energy photon domain. The presence of the fully modelled plaque (including metal backing and plastic insert as opposed to just the seeds) increased variations between the codes. TPS doses show larger disagreements, with local dose differing by 2% on average and by as much as 8% at some points.
Conclusion: This work indicates that these MC codes exhibited excellent agreement for these test cases both in water and within an eye phantom, justifying their use as a benchmark. Further work will investigate discrepancies between the TPS and MC calculations, towards clinical applications of advanced dose evaluations.
Funding Support, Disclosures, and Conflict of Interest: Funding: Natural Sciences and Engineering Research Council (NSERC) of Canada, Canada Research Chairs, Ontario Ministry of Research and Innovation. COI: none.