Dose calculation of different eye substructures using a realistic eye model when treating ocular tumors with electron therapy

One of the most frequent types of intraocular melanoma in adults is choroidal uveal melanoma. The most commonly used forms of radiation therapy are ophthalmic plaque brachytherapy and charged particle external radiation therapy. In the absence of adequate facilities for brachytherapy and proton therapy, electron therapy would be an efficient radiation therapy technique for treating eye melanomas. In the present work, the Monte Carlo code MCNPX 2.6.0 was used to calculate the dose distribution to substructures of the eye in electron therapy of three common choroidal tumors. The simulations were performed for 6 electron beams with nominal energies between 5 MeV and 10 MeV and also for 10 incidence angles. To identify suitable treatment plans, the tumor-to-sensitive zone dose ratios were estimated. Moreover, the equivalent doses delivered to healthy substructures of the eye were also calculated. The results indicate that for the treatment of tumors located at the posterior part of the eye, an electron beam with energy of 10 MeV and incident angle of 45 degrees relative to the eye axis provides the best tumor coverage while optimally sparing other eye substructures. In addition, for tumors positioned on the upper and lower parts of the vitreous, electron beams with energy of 10 MeV, an azimuthal angle of 270 degrees, and polar incident angles of 90 degrees and 105 degrees, respectively, lead to appropriate dose delivery.