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

Abstract Background & Purpose 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. Materials and Methods 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 0.1cm3 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. Results 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 Conclusions 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.