ESTRO 2025 - Abstract Book

S1627

Clinical – äediatric tumours

ESTRO 2025

Purpose/Objective: Re-irradiation plays a crucial role in the salvage treatment of patients with recurrent central nervous system (CNS) malignancies, providing long-term control or palliative relief in some cases. While initial treatment protocols are well-defined, guidelines for pediatric CNS tumor re-irradiation are lacking.This retrospective study reviews our experience with re-irradiation at a tertiary center examining the clinical impact of re-irradiation, along with an assessment of treatment-related toxicities and overall survival following recurrence. Material/Methods: This study retrospectively analyzed pediatric patients who received re-irradiation for CNS tumors at Hospital Universitario Virgen del Rocío (Seville, Spain) between 2018 and October 2024. Ten patients were included, although one was lost to follow-up after treatment due to transfer to another center. Results: The median age was 8 years (range 3–15 years). Diagnoses included diffuse intrinsic pontine glioma (DIPG) (n=7), diffuse astrocytoma (n=1), germ cell tumor (n=1) and posterior fossa anaplastic ependymoma (n=1). The most common initial treatment regimen was 54 Gy in 30 fractions (70%) (range 40-59.4 Gy / 23-33 fractions). The median time to first relapse was 10.5 months (range 5–76 months), with 80% of relapses occurring locally. Re-irradiation regimens were varied: 20 Gy in 10 fractions (n=2), 19.8 Gy in 11 fractions (n=3), 21.6 Gy in 12 fractions (n=1), 18 Gy in 10 fractions (n=1), 28.8 Gy in 16 fractions (n=1), 23.4 Gy in 13 fractions (n=1) and 36 Gy in 20 fractions (n=1). The median follow-up was 9 months (range 2–55). The 6-month OS rate was 50%, and the 1-year OS rate was 25%. The median OS after re-irradiation was 6 months. Three patients remain alive: one DIPG and two non-DIPG. For DIPG, median OS was 4 months, while for non-DIPG CNS tumors, it was 55 months. In 77.7% of patients, re-irradiation improved or controlled symptoms, while 33.3% did not experience improvement. Treatment was well tolerated: 33.3% experienced grade 1 toxicity and 11% grade 2 toxicity, with no grade 3 or 4 toxicities. We analyzed the relationship between symptom improvement after radiotherapy and survival using Kaplan-Meier and log-rank tests. A significant difference was found (p=0.0155), indicating that patients who improved had better survival. Additionally, time to relapse correlated with post-recurrence survival (p=0.0046), suggesting longer relapse times predict better survival.