S1022
Clinical – Paediatric tumours
ESTRO 2026
fractions (81.8%), while re-RT dose regimens varied (range 19.8–54.0 Gy). Target volumes at re-irradiation had a median of 41.0 cc. Treatment fields included whole-brain (45.5%), focal (27.3%), and craniospinal irradiation (27.3%). Organ-at-risk tolerance limits were maintained for brainstem, spinal cord and optic pathways with a median total EQD2 of ≤ 77.5 Gy, ≤ 37.2 Gy and ≤ 60 Gy, respectively. Radiological response, with a median of 2 months after re-RT, demonstrated stable disease in 45.5%, partial response in 18.2%, and progression in 36.4%. Median interval from initial RT to re-RT was 12.8 months (range 3.4–81.0), with a median time to progression post–re-RT of 3.9 months and median overall survival from diagnosis of 33.7 months (range 14.5–61.7). Post- re-irradiation disease progression was associated with a median overall survival of 3.1 months. Acute toxicities were predominantly grade 1–2 alopecia (50%), erythema ≤ G3 (30%), and fatigue (10%), with no grade 4–5 events.
possibly reflecting greater accuracy in dose estimates or a publication bias. Standardised cardiac contouring, inclusion of substructure metrics, and harmonised dose reporting are needed to guide the development of validated paediatric dose-response models. References: [1] Bates JE, Rancati T, Keshavarz H, Gagliardi G, Aznar MC, Howell RM, et al. Cardiac Disease in Childhood Cancer Survivors Treated With Radiation Therapy: A PENTEC Comprehensive Review. Int J Radiat Oncol Biol Phys 2023.
https://doi.org/10.1016/j.ijrobp.2023.03.045. Keywords: Cardiac dose, Paediatric cancer, radiotherapy
Digital Poster 4121 Re-irradiation in Paediatric Brain Tumors: Cumulative Dose Limits, Treatment Toxicities and Disease Control — A Single-Center Retrospective Analysis. Catarina van der Elzen, Fátima Aires, Patrícia Varzim, Fernando Costa, Gabriel Farinha, Ana Rita Figueira, Lígia Osório Radiation Therapy, Unidade Local de Saúde de São João, Porto, Portugal Purpose/Objective: Recurrent/progressive pediatric brain tumors pose significant therapeutic challenges with limited salvage options. Re-irradiation (re-RT) may offer survival benefit and local control in highly selected patients. This study aimed to evaluate clinical outcomes, toxicity, and cumulative dosimetric parameters in pediatric patients undergoing re-irradiation for recurrent/progressive Central Nervous System (CNS) tumors using modern conformal techniques. Material/Methods: A retrospective cohort of 11 pediatric patients (median age 7.0 years; 63.6% female) with recurrent/progressive CNS malignancies was analyzed. Tumor histologies included diffuse intrinsic pontine glioma/diffuse midline glioma (DIPG/DMG) (45.5%), ependymomas (27.3%), and other rare entities. Most lesions were located in the brainstem (45.5%). Re- irradiation was performed using volumetric- modulated arc therapy (VMAT) or fractionated stereotactic VMAT (FSRT-VMAT). Cumulative biological effective dose (BED) and equivalent dose in 2 Gy fractions (EQD2) were calculated for critical structures. Radiological response, survival outcomes, and acute toxicities were assessed. Median follow-up was 39.7 ± 28.2 months. Results: All patients successfully completed re-irradiation. Initial RT was primarily delivered with 54.0 Gy in 30
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