Normal tissue complication probability (NTCP) models could aid the understanding of dose-dependence of radiation-induced toxicities after eye-preserving radiotherapy of choroidal melanomas. We performed NTCP-modelling and established dose-response relationships for visual acuity deterioration and common late complications after treatments with proton therapy (PT).
Retrospective study from single large referral centre.
We considered patients diagnosed with choroidal melanoma and primarily treated with hypo-fractionated PT (52 Gy physical dose in 4 fractions). 1020 patients had complete visual acuity deterioration information, 991 patients had complete information on late complications.
Treatment details and dose-volume histograms (DVHs) for relevant anatomical structures and patient and tumour characteristics were available from a dedicated ocular database. Lasso variable selection was used to identify variables with the strongest impact on each endpoint, followed by multivariable Cox regressions and logistic regressions to analyse the relationship between dose, clinical characteristics and clinical outcomes. Dose-response relationships were estimated, adjusting for relevant clinical variables.
Dose-response relationship for visual acuity deterioration and late complications RESULTS: Dose metrics for several structures (i.e. optic disc, macula, retina, globe, lens, ciliary body) correlated with clinical outcome. The near-maximum dose to the macula (macula D) showed the strongest correlation with visual acuity deterioration. Retina D was the only variable with clear impact on the risk of developing maculopathy; optic disc D had the largest impact on optic neuropathy; cornea D had the largest impact on neovascular glaucoma; ciliary body D had the largest impact on ocular hypertension; the volume of the ciliary body receiving 26 Gy (ciliary body V) was the only variable associated with the risk of cataract; and retina V was associated with the risk of retinal detachment. Optic disc-tumour distance was the only variable associated with dry eye syndrome in the absence of DVH for the lachrymal gland.
Visual acuity deterioration and specific late complications demonstrated dependence on dose delivered to normal structures in the eye after PT for choroidal melanoma. Visual acuity deterioration depended on dose to a range of structures, while more specific complications were primarily related to dose metrics for specific structures.

Copyright © 2020. Published by Elsevier Inc.