East Asian multi-centre study on clinical long-term outcomes of postoperative proton beam therapy for localised paediatric intracranial ependymoma.

Background: Postoperative proton beam therapy (PBT) has shown potential benefits for paediatric intracranial ependymoma; however, further evidence is needed. This study evaluated survival outcomes and toxicity in an East Asian multi-centre cohort. Materials and methods: We retrospectively analysed patients aged <20 years who underwent postoperative PBT for intracranial ependymoma at eight institutions in Japan and China between 2000 and 2023. Overall survival (OS) and progression-free survival (PFS) were estimated using the Kaplan-Meier method, while local failure was evaluated using the cumulative incidence function. Late adverse events were graded according to the Common Terminology Criteria for Adverse Events (CTCAE), version 4.0. Prognostic factors for OS, PFS, and local control (LC) were analysed. Results: Seventy-one patients were included (median age at PBT, 5.4 years). WHO Grade 3 ependymomas accounted for 73.2% of cases, and 59.2% were infratentorial. Gross total resection (GTR) was achieved in 64.8% of patients. The median prescribed dose was 59.4 Gy (RBE), and median follow-up was 45.5 months. The 3- and 5-year OS rates were 93.6% and 76.9%, respectively; PFS rates were 71.7% and 66.8%; and LC rates were 88.4% and 83.5%. Grade ≥ 2 late adverse events were uncommon; radiation necrosis in one patient (1.4%) and secondary malignancies in two (2.8%). On multivariate analysis, female sex and supratentorial location were independently associated with improved OS and PFS, and higher dose with improved OS. GTR tended to improve LC. Conclusions: Postoperative PBT is associated with favourable clinical outcomes and an acceptable toxicity profile in paediatric intracranial ependymoma.