How ten-years of reirradiation for paediatric high-grade glioma can shed light on first line treatment

Purpose: . Recurrence incidence for paediatric/adolescent high-grade glioma(HGG) exceeds 80%. Reirradiation(reRT) palliates symptoms and delays further progression. Strategies for reRT are scarce: we retrospectively analysed our series to develop rational future approaches. Methods: . We re-evaluated MRI+RT plans of 21 relapsed HGG-patients, accrued 2010-2021, aged under 18 years. All underwent surgery and RT+chemotherapy at diagnosis. Pathologic/molecular re-evaluation allowed classification based on WHO 2021 criteria in 20/21 patients. Survival analyses and association with clinical parameters were performed. Results: . Relapse after 1 st RT was local in 12(7 marginal), 4 disseminated, 5 local+disseminated. Re-RT obtained 8 SD, 1 PR, 1PsPD, 1 mixed response, 10 PD; neurological signs/symptoms improved in 8. Local reRT was given to 12, followed again by 6 local(2 marginal) and 4 local+disseminated second relapses in 10/12 re-evaluated. The 4 with dissemination had 1 whole brain, 2 craniospinal irradiation(CSI), 1 spine reRT and further relapsed with dissemination and local+dissemination in 3/four assessed. Five local+disseminated tumours had 3 CSI, 1 spine reRT, further progressing locally(2), disseminated(1), n.a.(1). Three had a third RT; three were alive at 19.4, 29, 50.3 months after diagnosis. Median times to progression/survival after re-RT were 3.7 months (0.6-16.2 months)/6.9 months (0.6-17.9 months), improved for longer interval r between 1 st RT and re-RT(P=0.017) and for non-PD after reRT(P< 0.001). First marginal relapse showed potential association with dissemination after re-RT(P= 0.081) Conclusions: . This is the biggest series of re-RT in paediatric HGG. Considering the dissemination relapse incidence observed, our results could prompt the investigation of first RT fields in a randomized trial.