Clinical outcomes in a large pediatric cohort of patients with ependymoma treated with proton radiotherapy

Background Treatment for pediatric ependymoma includes surgical resection followed by local radiotherapy (RT). Proton RT (PRT) enables superior sparing of critical structures compared with photons, with potential to reduce late effects. We report mature outcomes, patterns of failure, and predictors of outcomes in patients treated with PRT. Methods One hundred fifty patients (<22 y) with World Health Organization grades II/III ependymoma were treated with PRT between January 2001 and January 2019 at Massachusetts General Hospital. Demographic, tumor, and treatment-related characteristics were analyzed. Event-free survival (EFS), overall survival (OS), and local control (LC) were assessed. Results Median follow-up was 6.5 years. EFS, OS, and LC for the intracranial cohort (n = 145) at 7 years were 63.4%, 82.6%, and 76.1%. Fifty-one patients recurred: 26 (51.0%) local failures, 19 (37.3%) distant failures, and 6 (11.8%) synchronous failures. One hundred sixteen patients (77.3%) underwent gross total resection (GTR), 5 (3.3%) underwent near total resection (NTR), and 29 (19.3%) underwent subtotal resection (STR). EFS for the intracranial cohort at 7 years for GTR/NTR and STR was 70.3% and 35.2%. With multivariate analysis, the effect of tumor excision persisted after controlling for tumor location. There was no adverse effect on disease control if surgery to RT interval was within 9 weeks of GTR/NTR. Conclusion PRT is effective and safe in pediatric ependymoma. Similar to previous studies, GTR/NTR was the most important prognostic factor. Intervals up to 9 weeks from surgery to PRT did not compromise disease outcomes. There was no LC benefit between patients treated with >54 Gray relative biological effectiveness (GyRBE) versus ≤54 GyRBE.