Abstract
a variety of concave eye applicators with beta-ray sources, such as 90Sr/90Y and 106Ru/106Rh, are usually used in brachytherapy treatment of superficial intraocular tumors as uveal melanoma. However, in this study, a new plaque with 66Ni/66Cu beta-ray source has been designed and proposed. 66Ni/66Cu is an ideal radio isotope for this kind of brachytherapy due to its suitable half-life and beta energy. In this work, the designed 66Ni/66Cu plaque is compared with 90Sr/90Y and 106Ru/106Rh plaques which are more commonly used in this kind of treatment. The aim of this work is based on calculating the 3D dose distribution induced by beta-ray eye applicators on a mathematical model of the human eye using the Monte Carlo code MCNPX in order to treat a posterior uveal melanoma with 3.5 mm thickness from the choroid surface and compare the results. Three mathematical models were developed for 90Sr/90Y, 106Ru/106Rh and 66Ni/66Cu ophthalmic applicators. The mathematical model of applicators were attached to the eye model in order to calculate the dose distribution using the MCNPX *F8 tally. The average dose rate in all regions of the eye model was assessed. The *F8 tally results showed that the deposited energy due to the applicator with the radionuclide 106Ru/106Rh is higher in all eye regions, including tumor. However the relative energy deposition in the tumor compared to the lens is significantly higher for the 66Ni/66Cu applicator, with a factor of 88 to 1, whereas this ratio is 22 to 1 and 40 to 1 for 90Sr/90Y and106Ru/106Rh plaques respectively. Therefore, the 66Ni/66Cu applicator delivers a high amount of dose to the tumor without inflicting a drastic effect to the lens. This feature of 66Ni/66Cu plaque makes it a better option for critical organ safety in this kind of treatment compared to 90Sr/90Y and106Ru/106Rh plaques. zz