Feasibility and Safety of High‐Dose Proton Re‐Irradiation in Recurrent Pediatric Central Nervous System Tumors: A Single‐Institution Retrospective Study

PURPOSE: Pediatric central nervous system (CNS) tumors often recur despite multimodality therapy. Although re-irradiation (re-RT) has historically been limited by concerns for severe late toxicities, modern techniques have renewed interest in this approach. Proton therapy provides dosimetric advantages that may enable curative re-treatment with reduced normal tissue exposure. METHODS: We retrospectively reviewed 54 pediatric patients who underwent proton re-RT for recurrent CNS tumors at our institution (2010-2024). Eligible patients had received prior CNS-directed RT at ≤20 years of age. Toxicities were graded per Common Terminology Criteria for Adverse Events (CTCAE) v5.0 as acute (<3 months) or late (≥3 months). Cumulative dosimetry was assessed by registering RT1 and RT2 plans and converting doses to EQD2 (α/β = 2 Gy). Overall survival (OS) and progression-free survival (PFS) were estimated using Kaplan-Meier methods. RESULTS: of 109.0 Gy; only one patient developed Grade 3 radiation necrosis (RN). High-grade acute toxicity occurred in 13.0% of patients, all manageable with supportive care. CONCLUSION: Proton re-RT for pediatric CNS tumors is feasible and associated with encouraging survival and low rates of serious late toxicity.