A Comparison of Treatment Outcomes after Standard Dose (70 Gy) versus Reduced Dose (50 Gy) Proton Radiation in Patients with Uveal Melanoma.

Objective: To compare outcomes in a large patient cohort with small-medium tumors located within 1 disc diameter (DD) of the optic nerve and/or fovea treated with 50 Gy or 70 Gy proton therapy.

Design: Retrospective cohort study. Subjects: A total of 1120 patients with uveal melanomas ≤ 15 mm in largest basal diameter, ≤ 5 mm in height, located within 1 DD of the optic nerve and/or fovea, who received primary treatment with protons between 1975 and 2016 at Massachusetts Eye and Ear/Massachusetts General Hospital.

Methods: The rates of outcomes were estimated using the Kaplan-Meier method. Differences between the radiation dose groups were tested using the log-rank test. Main outcome measures: Local tumor recurrence, melanoma-related mortality, and visual acuity preservation (≥ 20/200, ≥ 20/40).

Results: Local tumor recurrence was observed in 1.8% of the 50 Gy group and 1.5% of the 70 Gy group. The median time to recurrence was 30.7 months for patients treated with 50 Gy and 32.0 months for those treated with 70 Gy (P = 0.28). Five-year rates of vision retention (≥20/40, ≥ 20/200) were 19.4% and 49.3% for patients treated with 50 Gy and 16.4% and 40.7% in those treated with 70 Gy. Ten-year rates of melanoma-related mortality were 8.4% in the 50 Gy group and 8.9% in the 70 Gy group (P = 0.47).

Conclusions: Comparable rates of local control are achieved treating small-medium tumors near the optic nerve and/or fovea with 50 Gy or 70 Gy proton therapy, supporting the use of the lower dose in patients with these tumor characteristics.