152 Re-irradiation for recurrent paediatric diffuse midline glioma: an international, multi-institutional retrospective study

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Abstract Introduction Children with recurrent diffuse midline gliomas (DMG) have limited therapeutic options at recurrence. Re-irradiation (RT2) may be used at progression but with uncertainty about benefit. Method We conducted a multi-institutional retrospective study of children aged <18 with DMG treated at three centres (Toronto, Canada; Birmingham, UK; Nottingham, UK). Patients with radiologic progression after first radiation (RT1) were included. Overall survival (OS) was calculated from the date of progression after RT1. Survival was analysed using Kaplan–Meier and log-rank test. Multivariable Cox regression identified independent predictors of OS. Results 167 patients were included with median age 7.9 years; 54 (32%) received RT2. Children selected for RT2 had longer interval from RT1 to progression (9.5 vs 5.9 months, p < 0.0001). Median OS from progression was longer in the RT2 group (7.1 months) compared to the no RT2 cohort (2.5 months; p < 0.0001). Six-month OS was 68% vs 16% and 1-year OS was 19% vs 3%, respectively. Patients needing RT2 ≥1 year after RT1 had superior survival compared with earlier RT2 (9.7 vs 5.0 months; p = 0.0041). Higher RT2 dose (≥30.6 Gy) showed a non-significant trend towards longer OS (p = 0.086). In multivariable analysis, use of RT2 was the strongest independent predictor of survival (HR 0.29, 95% CI 0.20–0.42; p < 0.0001). Older age at RT1 and clinical trial enrolment were also associated with improved survival. Conclusions In this large, multi-institutional international cohort, children with DMG treated with re-irradiation at progression showed a survival benefit, supporting re-irradiation as a key component of salvage therapy.