NCOG-46. Safety and efficacy of re-irradiation with salvage craniospinal irradiation for recurrent pediatric central nervous system malignancies

BACKGROUND Few studies have investigated the safety and outcome of re-irradiation with craniospinal irradiation (CSI). Our study aims to characterize clinical outcomes, including toxicity, and correlate outcomes with dosimetric parameters after photon re-irradiation with CSI. METHODS This single-institution retrospective study was approved by the IRB. Inclusion criteria included <21 years at diagnosis, definitive RT at initial diagnosis, and CSI as part of treatment at relapse or secondary malignancy from 2013-2025. Patients with <1 month of follow-up were excluded. Clinical and treatment characteristics were recorded. Kaplan-Meier method was used to assess overall survival (OS) and progression-free survival (PFS). Toxicities were graded using CTCAE v5. RESULTS Of the 9 patients in the cohort, 5 (55.6%) were female. Median age at diagnosis was 4.6 years (range: 0.2-17.0). The most common histology was medulloblastoma (n=3). At diagnosis, 6 patients received CSI and 3 received focal RT. Median dose of first RT was 54 Gy (range: 21.6-59.4) and 8 patients received proton RT at diagnosis. Median time to first relapse was 15.9 months (range: 2.3-94.0). Location of first recurrence was brain (n=5), spine (n=1), or both brain and spine (n=3). Six patients received chemotherapy and five received additional radiotherapy before re-irradiation with CSI. All patients had progression noted ≥2 times radiographically prior to salvage CSI. Median dose of salvage CSI was 24 Gy (range: 18.0-30.6) and median dose to any boost volume was 30 Gy (range: 25-36 Gy). Median follow-up was 7.0 months (range: 2.2-92.4 months), and PFS and OS at 6 months were 55.6% and 77.8%, respectively. No grade ≥2 CNS toxicity was observed. Five patients experienced grade ≥3 acute hematologic toxicity. CONCLUSIONS Re-irradiation with CSI can be a safe option and provide local control; median follow-up time remains short and cumulative doses to critical organs at risk remain important considerations for this approach.