Quantification of radiation retinopathy after beam proton irradiation in centrally located choroidal melanoma.

Purpose: To localize and quantify ischemic changes induced by proton beam irradiation of central choroidal melanoma and to identify baseline predictors correlated with the extent of ischemic changes.

Methods: Retrospective chart review of patients with central choroidal melanoma treated by proton beam irradiation and conducted widefield fluorescein angiography (≥ 20 months after radiation therapy). Quantification and location of ischemic areas and correlation to baseline predictors. Multiple linear regression model was performed for analyses.

Results: Twenty-five eyes from 25 patients were included in final analysis. Mean largest basal tumor area was 56.6 ± 40.0 mm and mean maximal tumor prominence 2.5 ± 1.4 mm. Mean total radiated area was 339.1 ± 68.3 mm. All patients showed ischemic changes. Mean ischemic area was 387.6 ± 123.3 mm and mean ischemic index (ischemic area/total visible area) was 0.53 ± 0.23. Twenty-two patients (88%) presented ischemic changes outside of the irradiation field, which comprised of 23% of total ischemic area. Mean angular distance between lateral border of irradiation field and ischemic area outside of the radiated area was 44.8 ± 36.5°. Multivariable analysis revealed a positive correlation of total ischemic area with total radiated area (p = 0.02) and initial sonographic tumor prominence (p = 0.02).

Conclusions: Ischemic changes induced by proton beam irradiation of central choroidal melanoma were localized and quantified. Ischemic changes exceed the tumor area distinctly and are found also outside of the irradiation field in the majority of patients. Size of irradiation area and tumor prominence are positively correlated with extent of ischemic area.