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

Pediatr Blood Cancer. 2026 Jul;73(7):e70371. doi: 10.1002/1545-5017.70371. Epub 2026 May 4.

Abstract

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: Median age at re-RT was 11 years, with a median interval of 28.5 months between RT courses. The median prescribed re-RT dose was 54 Gy (range, 25-60), yielding a cumulative EQD2 of 102.6 Gy (range, 46.8-112.9). Median OS and PFS were 46.0 and 16.5 months, respectively. Among 16 ependymoma patients, all received full-dose proton re-RT (54-59.4 Gy), yielding a 1-year OS of 91.7% and PFS of 50.0%. Glioma patients had inferior outcomes (1-year OS 55.4%, PFS 41.6%) with a median re-RT EQD2 of 48.1 Gy. An RT interval of ≥12 months was associated with improved OS and PFS. Composite dosimetry in 21 patients showed a median cumulative brain D0.1cc 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.

Keywords: neuro‐oncology; pediatric CNS tumors; proton therapy; radiation oncology; re‐irradiation.

MeSH terms

  • Adolescent
  • Central Nervous System Neoplasms* / mortality
  • Central Nervous System Neoplasms* / pathology
  • Central Nervous System Neoplasms* / radiotherapy
  • Child
  • Child, Preschool
  • Feasibility Studies
  • Female
  • Follow-Up Studies
  • Humans
  • Infant
  • Male
  • Neoplasm Recurrence, Local* / pathology
  • Neoplasm Recurrence, Local* / radiotherapy
  • Prognosis
  • Proton Therapy* / adverse effects
  • Proton Therapy* / methods
  • Proton Therapy* / mortality
  • Radiotherapy Dosage
  • Re-Irradiation* / adverse effects
  • Re-Irradiation* / methods
  • Re-Irradiation* / mortality
  • Retrospective Studies
  • Survival Rate
  • Young Adult