Histopathologic study of eyes after iodine I 125 episcleral plaque irradiation for uveal melanoma

Objectives: To describe the histopathologic findings attributable to irradiation in eyes with uveal malignant melanoma treated with iodine I 125 brachytherapy and to compare these findings with those reviewed in a previous study that compared histopathologic findings in eyes enucleated after proton beam teletherapy with those seen in eyes in a nonirradiated control group. Methods: The slides from 22 eyes with uveal melanoma that had undergone enucleation after the administration of ¹²⁵I brachytherapy were studied. The histopathologic features of the tumor and the retina were graded. Results were compared with findings from a previously reported group of 47 proton beam-treated eyes and its control group. Results: Patient age, time between irradiation and enucleation, and ciliary body involvement were similar for the ¹²⁵I brachytherapy-treated group and the proton beam- treated group and its control group. This allows comparison of the histopathologic findings. Comparing the ¹²⁵I brachytherapy-and proton beam-treated groups, most histopathologic features were similar with nominally statistically significant differences only for cell type, number of mitotic figures, and fibrous metaplasia of the retinal pigment epithelium adjacent to the tumor. Conclusions: Irradiation of uveal melanoma induces changes in the tumor and in the surrounding retina. Brachytherapy and charged particle therapy are the 2 principal methods of irradiation. This study demonstrates that similar changes are produced by ¹²⁵I plaque irradiation and proton beam irradiation.