ESTRO 2025 - Abstract Book

S1613

Clinical – äediatric tumours

ESTRO 2025

533

Mini-Oral Reirradiation for Recurrent Diffuse Intrinsic Pontine Glioma and Diffuse Midline Glioma is associated with Improved Survival Nisha Shariff 1 , Alejandro S. Moreno 1 , Julie Bennett 2 , Vijay Ramaswamy 2 , Anirban Das 2 , Anthony P. Liu 2 , Annie Huang 2 , Uri Tabori 2 , Cynthia Hawkins 2 , Peter Dirks 3 , Eric Bouffet 2 , Dana M. Keilty 1 , Barbara A. Millar 1 , David C. Hodgson 1 , Derek S. Tsang 1 1 Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Canada. 2 Neuro-Oncology Division of Hematology/Oncology, Hospital for Sick Children, Toronto, Canada. 3 Division of Neurosurgery, Hospital for Sick Children, Toronto, Canada Purpose/Objective: Diffuse intrinsic pontine glioma (DIPG) and diffuse midline glioma (DMG) are incurable diseases with no curative treatment options. Radiation remains the standard of care, with reirradiation (RT2) increasingly given as a palliative treatment. In this study, we report one of the largest known cohorts of DIPG/DMG patients undergoing RT2 to evaluate its effect on survival. Material/Methods: Patients aged less than 18 years treated for DIPG/DMG between January 1998 and February 2024 with an initial course of fractionated photon radiotherapy (RT1) and subsequent recurrence were retrospectively reviewed. The most common radiation dose for RT1 was 5400cGy in 30 fractions (96%); and for RT2, 3060cGy in 17 fractions (56%), 2000cGy in 10 fractions (18%), 3600cGy in 20 fractions (8%). The primary outcome was overall survival (OS), with an index time at the date of radiologic or clinical progression after RT1, excluding pseudoprogression. Results: A total of 118 children treated with radiation were included, with a median age of 7.7 years. A total of 38% of all tumors underwent biopsy; non-brainstem DMG with confirmed H3K27M accounted for 9% of the cohort. 39 patients received RT2 (33%). Two patients did not complete RT2, one of whom died during treatment; both were included. Children who received RT2 had superior survival from time of progression after RT1, with 6-month OS of 66% (95% CI 49-79) vs 22% (95% CI 13-31, p < 0.0001) for children who did not receive RT2; median survivals were 6.9 months vs 2.7 months, respectively. The median time from RT1 to RT2 was 7.7 months (IQR 6.3-12.0 months); patients with a greater than 1-year latent time between RT1 and RT2 had better survival from start of RT2 (median survivals were 10.9 months vs 5.5 months, p = 0.023). Multivariate analysis identified younger age, any adverse imaging findings on the 4-week post-RT1 reassessment MRI (including pseudoprogression), and the omission of RT2 as poor prognostic factors for OS. Histological grade (if biopsied), tumor location, use of any systemic therapy or bevacizumab were not associated with survival.