ESTRO 2022 - Abstract Book

S987

Abstract book

ESTRO 2022

biomathematical modelling to hypothesize dose-response-relationship curves for clinically applied radiation schedules for the treatment of glioblastoma to hypothesize whether dose-escalation might possibly be promising in this clinical setting. Materials and Methods A literature research was performed to retrieve clinical data of glioblastoma patients treated with different radiation schedules and total treatment doses combined with temozolomide. Progression-free survival rates (PFS) at 6 months and 12 months were recorded. PFS at 6 months (weighted by the number of patients included in the respective study) was fitted with a linear-quadratic model and optimized manually. Dose-response-curves were calculated for PFS at 6 months. Results 27 studies were identified with different fractionation schedules and total treatment doses. In all studies, patients were treated with combined radiochemotherapy with temozolomide. The studies had included between 10 and 287 patients. PFS at 6 and 12 months ranged from 0.43 to 0.90 and 0.20 to 0.76, respectively. The linear-quadratic fit showed a good correlation with r=0.68 for PFS at 6 months. The applied fractionation schedules are in the steep part of the dose-response curve. Conclusion Clinical data of patients treated with radiotherapy with different fractionation schedules and total radiation dose were well fitted by a radiation dose response curve based on the linear quadratic model. PFS at 6 months showed that clinically applied radiation schedules are located in the steep part of the dose-response-curve. Thus, even limited dose escalation might be hypothesized to have a clinical benefit for the treatment outcome of glioblastoma patients. 1 Bordeaux University Hospital, Radiotherapy, Bordeaux, France; 2 Bordeaux University Hospital, Radiotherapy , Bordeaux, France; 3 Bordeaux University Hospital, Medical oncology, Bordeaux, France Purpose or Objective Re-irradiation is an option for the treatment of high-grade gliomas recurrence. However, there is no recommendation regarding dose, fractionation or target volume. Our retrospective monocentric study aims to analyze progression-free survival (PFS), overall survival (OS) and the tolerance of glioblastoma re-irradiation. Materials and Methods We identified all patients treated by re-irradiation for high-grade glioma between 2014 and 2021 at Bordeaux University Hospital. Evaluation included overall survival, progression-free survival, and treatment-related toxicities. For each patient, IDH status and Bevacizumab association were detailed. Results 42 patients (median age 59 years [31; 75]; median WHO 1) were retreated for high-grade glioma recurrence (IDH-negative 78.5%). Median time between initial irradiation and re-irradiation was 12.7 months [1.7-314]. Median re-irradiation dose was 30 Gy [18-62.7] with a median volume (PTV) of 12.3 cm ³ [0.4-299]. Median OS after re-irradiation was 14.3 months [8.5; 20.1] and median PFS was 4.7 months [3; 6.5]. Radionecrosis was observed in 17 patients (40%), with only 2 symptomatic patients: headaches grade 2 and epileptic fit grade 3. Median OS of patients treated prior to re-irradiation with Bevacizumab was 4.9 months and median PFS was 2.6 months. When Bevacizumab was used during or after radiotherapy, median OS after re-irradiation was 15.8 months and median PFS was 6.2 months. PO-1164 Prolonged overall survival for IDH negative glioblastomas recurrence with re-irradiation G. Marie 1 , L. Mathilde 2 , B. Charlotte 3 , T. Renaud 1 , S. Catherine 1 , V. Veronique 1 , H. Aymeri 1

Conclusion Re-irradiation of high-grade gliomas is a well-tolerated treatment with encouraging results for patients with IDH-negative glioblastomas.