RTHP-17. PATTERNS OF RE-IRRADIATION FOR RECURRENT GLIOMAS AND VALIDATION OF A PROGNOSTIC SCORE

Abstract Re-irradiation is a generally accepted method for salvage treatment in patients with recurrent glioma. However, no standard radiation regimen has been defined. This study aims to compare the efficacy and safety of different treatment regimens and to independently externally validate a recently published reirradiation risk score. We retrospectively analyzed a cohort of patients with recurrent malignant glioma treated with salvage conventionally fractionated (CFRT), hypofractionated (HFRT) or stereotactic radiotherapy (SRT) between 2007 and 2017 at the University Medical Center in Utrecht and Groningen. Moreover, we validated the reirradiation risk score. Of the 121 patients included, 60 patients (50%) underwent CFRT, 22 (18%) HFRT and 39 (32%) SRT. The primary tumor was grade 2/3 in 52 patients and grade 4 in 69 patients with median Overall Survival (mOS) since first surgery of 113 [Interquartile range: 53.2–137] and 39.7 [24.6–64.9] months respectively (p< 0.01). Overall, mOS from the first day of re-irradiation was 9.7 months [6.5–14.6]. No significant difference in mOS was found between the treatment groups. In multivariate analysis, Karnofsky performance scale 70% (p< 0.01), re-irradiation for first recurrence (p= 0.02), longer time interval (p< 0.01) and smaller planning target volume (p< 0.05) were significant favorable prognostic factors. The reirradiation risk score was validated. In our series, mOS after reirradiation was sufficient to justify more use of this modality. Until a reliable treatment decision tool is developed based on larger retrospective research, the decision for re-irradiation schedule should remain personalized and based on a multidisciplinary evaluation of each patient.