The Relationship of Radiation Dose to Critical Eye Structures to Loss of Visual Acuity After I-125 Brachytherapy for Choroidal Melanoma

Abstract

Abstract: : Purpose: To determine how radiation dose to critical eye structures (foveola, disc, and lens) relates to visual acuity outcome in patients treated with I-125 brachytherapy for choroidal melanoma, and to determine clinical and tumor characteristics that influence visual acuity outcome independently of radiation dose. Materials and Methods: From 1986 to 1997, 657 patients enrolled in the Collaborative Ocular Melanoma Study (COMS) clinical trial for medium-sized choroidal melanoma and were randomized to treatment with I-125 brachytherapy. Radiation doses to critical eye structures were computed using Plaque Simulator © treatment planning system, incorporating adjustments for I-125 seed anisotropy, attenuation through the silastic insert and gold plaque, backscatter from the gold plaque, and plaque rotation, for 600 patients who were treated using a standard COMS gold plaque. A Cox proportional hazards regression model was used to model probability of loss of 3 or more and 6 or more lines of visual acuity following treatment as a function of the radiation doses to critical eye structures for the 502 patients who had initial visual acuity of 20/200 or better and an intact lens and hence were at risk of significant loss of visual acuity due to radiation retinopathy, optic neuropathy, or cataract following treatment. The Cox model also was used to identify baseline clinical and tumor characteristics that significantly influenced visual acuity loss independently of radiation dose. Results: Loss of visual acuity was dependent on dose to the center of the foveola and center of the lens with a strong synergistic interaction between the 2 doses. Dose to the optic disc did not influence visual acuity loss after accounting for doses to the foveola and lens. Presence of diabetes, a non-dome-shaped tumor, and tumor-associated retinal detachment at baseline independently increased the probability of visual acuity loss. Probability of visual acuity loss also increased with time since treatment. Conclusion: These data suggest that retinopathy and cataract resulting from radiation-induced damage to the fovea and lens and not optic neuropathy are the primary mechanisms of visual acuity loss following I-125 brachytherapy for choroidal melanoma, with patient medical and tumor-related factors also playing some role.

Keywords: melanoma • clinical (human) or epidemiologic studies: tre • clinical (human) or epidemiologic studies: out