Monte Carlo investigation of dose distribution of two model Ru/Rh ophthalmic plaques in a realistic human eye model with different uveal melanoma size.

Uveal melanoma is the most common primary eye cancer with the highest incidence. BEBIG Ru/Rh ophthalmic plaques more used for the treatment of these eye malignancies, mainly malignancies with small to medium sizes. In this study, we evaluate dose distributions around a voxelized eye phantom due to CCA and CCB eye plaque using GATE code. The phantom contains the important eye substructures with three defined tumors with the same basal diameter and different apical thicknesses of 3 mm, 4 mm, and 5 mm. The validation for source and plaques have been performed by comparing the obtained results for energy spectrum of the source and percentage depth-dose along the central axis of plaques with the available published data. The delivered doses to the eye components and tumors show that received doses by different eye substructures depend on the size of the plaque and tumor thickness. Results show that the knowledge of the height of tumor apex before treating eye tumors with ophthalmic plaques is essential. On the other hand, about 32% (62%) of the dose deposition belongs to secondary produced photons in the CCA (CCB) plaque. Moreover, comparing the results obtained from two plaques, showed that although the CCB plaque produces a more uniform dose distribution in the tumor, the CCA plaque presents a higher dose delivery to the tumor and a lower one to the critical structures for all three tumor sizes. Therefore, it is recommended to use CCA plaque for eye tumors up to 5 mm height of the apex.