Vision loss following high-dose proton-based radiotherapy for skull-base chordoma and chondrosarcoma.

Abstract

Dose escalation for skull-based chordoma and chondrosarcoma can put critical adjacent structures at risk, specifically the anterior optic pathway. We report the incidence of vision loss following high-dose conformal proton-based radiotherapy. We reviewed patients with skull-base chordoma or chondrosarcoma treated with proton-based therapy between 2007 and 2018. We analyzed 148 patients and 283 individual eyes with functional vision at baseline who received a minimum 30GyRBE to 0.1 cm³ of the anterior optic pathway. Eyes were classified as "functionally blind" if visual acuity was 20/200 or worse. Kaplan-Meier and normal tissue complication probability modeling were used to establish the relationship between radiation dose and risk of functional vision loss. At last follow-up, 110 of 148 patients were alive with no evidence of disease progression. With a median follow-up of 4.1 years (range, 0.5-12.8), 5 eyes in 3 patients developed functional blindness, with 2 patients developing bilateral blindness. Median time to blindness was 15.2 months. The 5-year incidence of vision loss was 2.1% (95% CI: 0.9-4.9%). On univariate analysis, development of blindness was associated with presence of multiple medical comorbidities (p = 0.0040). While there were no events with a maximum dose < 60GyRBE delivered to the anterior optic pathway, the crude rate was 3.6% over 60GyRBE, with all events occurring between 60-65GyRBE. Despite the high radiotherapy dose delivered to patients with skull-base chordoma and chondrosarcoma, the rate of vision loss is low and no events occurred in those who received a maximum dose under 60GyRBE.