ESTRO 2025 - Abstract Book

S737

Clinical - CNS

ESTRO 2025

3904

Digital Poster Dose-escalated re-irradation of recurrent glioma – Analysis of risk of radionecrosis and symptomatic edema Daniel F. Fleischmann 1,2,3 , Laura Gajdi 1 , Stephan Schönecker 1 , Sebastian N. Marschner 1,2 , Raphael Bodensohn 4 , Jan Hofmaier 1 , Sylvia Garny 1 , Robert Forbrig 5 , Niklas Thon 6 , Stefanie Corradini 1 , Claus Belka 1,2,7 , Maximilian Niyazi 4,1,8 1 Department of Radiation Oncology, LMU University Hospital, LMU Munich, Munich, Germany. 2 German Cancer Consortium (DKTK), partner site Munich, a partnership between DKFZ and LMU University Hospital, Munich, Germany. 3 German Cancer Research Center, (DKFZ), Heidelberg, Germany. 4 Department of Radiation Oncology, University Hospital Tübingen, Tübingen, Germany. 5 Institute of Neuroradiology, LMU University Hospital, LMU Munich, Munich, Germany. 6 Department of Neurosurgery, LMU University Hospital, LMU Munich, Munich, Germany. 7 Bavarian Cancer Research Center, (BZKF), Munich, Germany. 8 German Cancer Consortium (DKTK), partner site Tübingen, a partnership between DKFZ and University Hospital Tübingen, Tübingen, Germany Purpose/Objective: Re-irradiation (re-RT) is an effective re-treatment option for recurrent glioma. The risk of radionecrosis (RN) increases with the cumulative total dose. In this analysis, we evaluated a large single-center group of patients with recurrent glioma treated with re-irradiation with or without dose escalation for the occurrence of RN on MRI and the occurrence of symptomatic edema (SE). Material/Methods: Patients with recurrent glioma undergoing re-RT without concomitant bevacizumab (BEV) at our center were included into this retrospective analysis. Dose summation was performed EQD2/2 scaled. Repair factors assuming half repair at 6 or 12 months after RT were applied, to account for different time intervals between primary and re RT. RN was detected on basis of follow-up MRI and verified by an experienced neuro-radiologist. SE was detected by edema on MRI in combination with clinical implications such as prolonged dexamethasone use. RN-free and RN/SE free survival were calculated both from the beginning of re-RT until the occurrence of RN or RN and/or SE, respectively. Cox regression was performed for RN- and RN/SE-free survival. Two dose groups were built with a median split. Results: 116 patients (74 male, 42 female, median age 56 years at re-RT) with recurrent glioma undergoing re-RT were included into the analysis. 65 patients were treated with ≤ 39.6 Gy (range 30.6 - 39.6 Gy) and 51 patients with > 39.6 Gy (range 40.0 - 43.2 Gy). Median interval between RT and re-RT was 16 months vs. 25 months and temozolomide was applied in 30.8 % vs. 29.4 % of cases, in the ≤ 39.6 and > 39.6 Gy dose groups, respectively. RN was present in 30.8 % vs. 33.3 %, and RN/SE in 35.4 vs. 37.3 % of cases, respectively. Regarding RN-free survival, no statistically significant difference could be detected in the cox regression, when comparing ≤ 39.6 vs. > 39.6 Gy. Regarding RN/SE-free survival, dose summation with a repair factor assuming half repair at 12 months showed statistical significance on univariable analysis (p = 0.033), whereas all other factors including PTV volume, concomitant TMZ and all other dose summation formulas had no statistical significance. Conclusion: Re-RT includes the risk of RN and RN/SE in about 1/3 of cases. The prediction of RN and RN/SE remains challenging especially in the era of dose-escalation without BEV being readily available in the re-RT setting. Complex dose summation models including repair seem to be the key for further insight for the prediction of RN and RN/SE.

Keywords: Glioma, Re-RT, Dose-Escalation