Corneal Substructure Dosimetry Predicts Corneal Toxicity in Patients With Uveal Melanoma Treated With Proton Beam Therapy

Purpose This study examines the relationship between dose to corneal substructures and incidence of corneal toxicity within 6 months of proton beam therapy (PBT) for uveal melanoma. We aim to develop clinically meaningful dose constraints that can be used to mitigate corneal toxicity. Methods and Materials Ninety-two patients were treated with PBT between 2015 and 2017 and evaluated for grade 2+ (GR2+) intervention-requiring corneal toxicity in our prospectively maintained database. Most patients were treated with 50 Gy (relative biological effectiveness [RBE]) in 5 fractions, and all had complete six-month follow-up. Analyses included Mann-Whitney, χ 2 , Fisher exact, and receiver operating curve tests to identify risk factors for GR2+ toxicity. Bivariate logistic regression was used to identify independent dose-volume histogram (DVH) predictors of toxicity after adjustment for the most important clinical risk factor. Results The 6-month PBT GR2+ corneal toxicity rate was 10.9%, with half of patients experiencing grade 2 toxicity and half experiencing grade 3 toxicity, with no grade 4 events. Patients with anterior chamber tumors had a higher risk (58.3%) for toxicity than those with posterior tumors (0%) or posterior tumors extending past the equator (25%, P P Conclusions Patients receiving PBT for anterior uveal melanomas experience a high rate of GR2+ corneal toxicity because of increased corneal dose. Anterior location and corneal DVH parameters independently predict toxicity risk. We propose dosimetric constraints to facilitate treatment planning and toxicity mitigation.