RADIATION EFFECTS ON THE OPTIC-NERVE OBSERVED AFTER BRACHYTHERAPY OF CHOROIDAL MELANOMAS WITH RU-106 RH-106 PLAQUES

From 1966 to 1990 a total of 93 juxtapapillary choroidal melanomas were treated using RU-106/Rh-106 plaques with a notch for the optic nerve. The choroidal melanoma was controlled after brachytherapy in 79 cases (85%). Fourteen eyes (15%) had to be enucleated because of tumor regrowth. Eye and optic nerve phantoms were fabricated, loaded with small-volume thermoluminescent dosimeters, treated with active plaques, and the radiation dose determined at the optic disc and along the optic nerve. The median dose within the anterior optic nerve was 51.2 Gy (range 10.3-60.5 Gy). The probability of developing complete radiation optic neuropathy (RON) was 23% and 53% at 5 and 10 years, respectively. The probability of developing partial RON was 66% at 5 years and 82% at 10 years. The probability of retaining visual acuity better than 0.5 was 38% at 5 years and 26% at 10 years. No dose-response relationship could be established from the ophthalmological. morphological and functional findings. Eyes following plaque irradiation with 50 Gy or more in the center of the optic nerve experienced significant radiation optic neuropathy, other eyes did not.