ESTRO 38 Abstract book

S387 ESTRO 38

[6.9-17.6], HFRT: 7.7 [5.7-10.3] and SRT: 9.7 [6.2-14.9] months (Figure 1)) . In multivariate analysis, Karnofsky performance scale ≥70% (p<0.01), ReRT for first recurrence (p=0.02), longer time interval between RT start dates (p<0.01) and smaller planning target volume (p<0.05) were significant favorable prognostic factors (Table 1). Eight patients (12.5%) developed severe, hospitalization required, acute toxicity and five cases (7.7%) of radionecrosis were reported in the UMC Utrecht dataset (n=65). The ReRT risk score showed good calibration by corresponding results of the Cox regression and Kaplan-Meier estimators (mOS of the prognostic groups in our cohort: 14.6, 9.76, 5.32 months versus Niyazi’s development cohort 14.2, 9.1 and 5.3 versus Niyazi’s validation cohort 13.8, 8.8 and 3.8 months). Discrimination performance of the score is modest (c- index: 0.65).

Conclusion This atlas was feasible and reproducible for the delineation of DVC on planning CT using fused MRI. It will be used to prospectively assess dose-volume relationship for DVC and occurrence of nausea vomiting during intracranial or head and neck irradiation. PO-0755 Patterns of Re-irradiation for Recurrent Gliomas and Validation of a Prognostic Score J. Verhoeff 1 , C. Post 1 , M. Kramer 2 , E. Smid 1 , H. Van der Weide 2 , K. Kleynen 1 , M. Heesters 2 1 UMC Utrecht, Radiation Oncology, Utrecht, The Netherlands ; 2 UMC Groningen, Radiation Oncology, Groningen, The Netherlands Purpose or Objective Re-irradiation (ReRT) 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 ReRT risk score introduced by Niyazi et al. (2018). Material and Methods We retrospectively analyzed a cohort of patients with recurrent malignant glioma treated with salvage conventionally fractionated (CFRT; fractional dose <3 Gray), hypofractionated (HFRT; fractional dose 3-5 Gray) or stereotactic radiotherapy (SRT; fractional dose ≥5 Gray) between 2007 and 2017 at the University Medical Centers of Utrecht and Groningen. Results Of the 121 patients included, 60 patients (50%) underwent CFRT, 22 (18%) HFRT and 39 (32%) SRT. The primary tumor was grade II-III in 52 patients and grade IV 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 and mOS from first day of ReRT of 8.5 [6.5-11.6] and 11.3 [6.3-28.5] months respectively. Overall, mOS post ReRT was 9.7 months [6.5- 14.6]. No significant difference in mOS was found between the treatment groups using log-rank test (p=0.17) and multivariate Cox regression (p=0.79) (mOS CFRT: 10.0

Conclusion In our series, mOS after ReRT was sufficient to justify use of this modality. Until a reliable treatment decision tool is developed based on larger retrospective research, the decision for ReRT schedule should remain personalized and based on a multidisciplinary evaluation of each patient.