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Episcleral Eye Plaque Dosimetry Comparison for the Eye Physics EP917 Using Plaque Simulator and Monte Carlo Simulation


L Zimmermann

L Zimmermann, MS1*, A Amoush, Ph.D.2, D Wilkinson, Ph.D.3, (1) ,Ceveland State University, (2) Cleveland Clinic Foundation, Cleveland, OH, (3) Cleveland Clinic Foundation, Cleveland, OH

SU-E-T-452 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
To compare the dosimetry calculated by the treatment planning software, Plaque Simulatorâ„¢, 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.

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