SU‐E‐T‐452: Episcleral Eye Plaque Dosimetry Comparison for the Eye Physics EP917 Using Plaque Simulator and Monte Carlo Simulation

Purpose: To compare the dosimetry calculated by the treatment planning software, Plaque Simulator™, to the dosimetry calculated using Monte Carlo methods. Methods: MCNPX 2.6.0 Monte Carlo Simulation (MC) code was used to model the Eye Physics model EP917 eye plaque. The IsoAid Advantage, IA1‐125A, 125I seed was also modeled using MCNPX and compared to published data by Meigooni et al. Energy deposition tally in unit of MeV/g was used to calculate the dose averaged over a cell.Bebig Plaque Simulator (PS) v574 treatment‐planning software was used to calculate the dose based on AAPM TG‐43U1 dose formalism; single factors are used to account for source collimation and backscattering from the gold alloy plaque.Relative doses, normalized to a prescription point of 6 mm (5 mm from the inner sclera surface), from MCNPX and PS, along the eye central axis from 1 mm to 12 mm from the scleral surface, were compared for a single seed in the plaque. Results: The IsoAid Advantage, IA1‐125A, 125I seed dose rate constant and radial dose function were calculated and agreed within 5% and 4% respectively with Meigooni et al. published data. For the central seed position, the dose differences between the MC simulation along the central axis of the eye at 1 mm and 2 mm from the scleral surface and the predicted doses by the Plaque Simulator were 32.4% and 15.2%, respectively. For distances from 3 mm to 12 mm from the scleral surface, MCNPX agreed with PS within 5%. Conclusion: For the first source position, Plaque Simulator underestimated the dose at 1 mm and 2 mm from the scleral surface by 32.4% and 12.5%. Beyond 3 mm, PS agrees within uncertainties with MCNPX results. Further investigation is needed to better identify the sources of these differences.