RADT-34. RE-IRRADIATION REGIMENS FOR RECURRENT GLIOMA: SURVIVAL AND TOXICITY

Abstract Re-irradiation is a common treatment option for recurrent high-grade glioma (HGG), though the optimal dose-fractionation regimen remains unclear. This report presents single-center data from an ongoing multicenter, retrospective study in the Netherlands. We included adult HGG patients treated with re-irradiation. Dose-fractionation regimens were categorized in 3 groups: conventionally fractionated radiotherapy (CFRT, <3Gy/fraction), hypofractionated radiotherapy (HFRT, 3-5 Gy/fraction) and stereotactic radiotherapy (SRT, ≥5Gy/fraction). We compared baseline characteristics, overall survival, and toxicity including incidence of radionecrosis between groups to identify the optimal dose-fractionation regimen. Of 112 patients, 33 underwent CFRT, 60 HFRT and 19 SRT. 21 patients had a good prognostic Niyazi score, 70 intermediate and 6 poor, with more poor scores in the SRT group. SRT patients had smaller median GTVs compared to HFRT and CFRT (1.9, 20.5, 32.8 respectively, p=0.003). Radiation groups also differed in primary histology (less grade 4 in CFRT, p=0.009), but not in age and KPS. Overall survival (OS) was worse for HFRT (median OS 9 months (95%-CI 6.5-11.5)) compared to CFRT (12 months (8.9-15.2, p=0.039)) and SRT (12 months (9.2-14.8, p = 0.012)), but did not differ between CFRT and SRT (p=0.437). In Cox regression, Karnofsky performance score <80 (hazard ratio (HR): 1.874, p=0.006) and large GTV (HR: 1.011, p=0.003) were independently associated with poor survival, while the fractionation schedule was not. Multivariable logistic regression on toxicity analysis indicated an increased risk of radionecrosis in the CFRT and HFRT groups compared to the SRT group (OR 5.861, p=0.011), even after adjusting for GTV and age. In conclusion, re-irradiation schemes in HGG are univariably, but not independently, associated with overall survival; this relationship seems to be confounded by differences in GTV and possibly by KPS. Radionecrosis was more common in HFRT and CFRT than in SRT. Extension and/or validation of findings will be performed in a multicenter cohort.