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Calculation of Dose Distributions From 106 Ruthenium COC-Type Eye Applicator

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M Futaguchi

M Futaguchi*[1], A Haga[1], A Sakumi[1], H Okamoto[2], M Hamada[2], M Fuse[2], Y Abe[2], N Murakami[2], J Itami[2], K Nakagawa[2], [1]University of Tokyo Hospital, [2]National Cancer Center Hospital

SU-E-T-338 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: In the treatment of retinoblastoma, 106Ru brachytherapy is one of the important methods to control the tumor with preserving eye function. So far, we had some clinical experiences that the tumor on optic disc was effectively shrunk by using the COC-type applicator (BEBIG), which has a notch. In this study, the dose distribution was evaluated by Monte Carlo simulation to investigate a dose to the notched area of COC applicator.
Methods: The model of the COC-type applicator was created and registered in EGS5 Monte Carlo simulation code. Here, the applicator thickness was 1mm including 0.1mm of the silver radiation window and 0.2 mm of radioactive layer. The notched area was also reproduced from the measurement of actual geometry. The dose to the notched area was represented with the polar coordinate, in which the two-dimensional relative dose distributions of the spherical shells with 0.2 mm thickness at distances of 0.1, 1.3, and 2.5 mm from the surface were calculated. For comparison, the dose profile was also calculated by the Plaque simulator (BEBIG).
Results: The Monte Carlo result showed that the scattered electron largely contributed to the dose to the notched area. This contribution became dominant as the distance from the surface was larger. The calculation result of the Plaque simulator was significantly different from that of the Monte Carlo simulation around the notched area of the applicator.
Conclusion:The dose distribution with the COC-type applicator could be quantified by the Monte Carlo Conclusion: The dose distribution with the COC-type applicator could be quantified by the Monte Carlo calculation. It was found that the notched area of COC-type applicator was irradiated sufficiently by the scattered electron. The Plaque simulator could not reproduce the dose distribution around the notched area.

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