ESTRO 2020 Abstract Book

S471 ESTRO 2020

and 2 lesions (0.8%) in 2 patients (3.1%) had been proven histopathologically as radiation necrosis. Conclusion According to the evaluation of the cohort so far, SRS using SIDCA seems to be a feasible and safe treatment for patients with multiple metastases. So far, the local and intracranial control rate seems promising as well. However, closer analysis will be needed, with more patients and a longer follow-up. PO-0877 Hypofractionated and single-fraction SRT for brain metastases with sex as a key predictor of OS J. Mangesius 1 , T. Seppi 1 , C.R. Arnold 1 , D. Minasch 1 , K. Bates 2 , M. Nevinny-Stickel 1 , U. Ganswindt 1 1 Medical University Innsbruck, Department for Therapeutic Radiology and Oncology, Innsbruck, Austria ; 2 Medical University Innsbruck, Department of Medical Statistics- Informatics and Health Economics, Innsbruck, Austria Purpose or Objective To compare overall survival outcome of patients with brain metastases treated with hypofractionated (HFSRT) or single-fraction (SRS) radiosurgery after long-term follow- up. To evaluate the power of common prognostic factors and scores for therapy decision-making, and to assess the potential of sex as an independent predictor of overall survival. Material and Methods Retrospective analysis of 281 consecutive patients receiving radio surgery for brain metastases was performed. A Kaplan-Meier survival curve and Cox proportional hazards multivariate analyses were used to compare overall survival between males and females, as well as between SRS and HFSRT, before and after propensity score matching. Prognostic scores were compared using Harrell’s concordance index. Results Median overall survival was 11 months after both SRS (95% CI: 7.5-14.5) and HFSRT (95% CI: 8.3-13.7 months; p = 0,99). After propensity score matching, median overall survival was 11 months after SRS (95% CI: 6.9-15.1) and 7 months after HFSRT (95%CI: 4.7-9.3; p = 0.135). Independent prognostic factors were sex, primary tumor, KPI, and systemic disease status. Median overall survival was 16 months for women and 7 months for male patients (p < 0.001). After excluding sex specific tumors and propensity matching, median overall survival was 16 months for women and 8 months for male patients p < 0.01). Evaluation of prognostic indices showed BSBM to be the most accurate (Harrell’s C = 0.68), followed by SIR (0.61), GPA (0.60), RPA (0.58), and Rades et al. (0.57).

Conclusion No difference in survival could be observed between HFSRT and SRS treated patients. Female sex was a major independent positive prognostic factor for survival. Sex and gender characteristics should be considered in the decision-making for the personalized treatment of patients with brain metastases. PO-0878 Improving dose distribution by adaptive radiotherapy for glioblastoma: A prospective study T. Matsuyama 1 , T. Watakabe 1 , T. Saito 1 , R. Toya 1 , N. Oya 1 1 Kumamoto University Hospital, radiation onoclogy, Kumamoto city, Japan Purpose or Objective The aim of this study was to analyze the efficacy of adaptive radiotherapy (ART) for glioblastoma (GBM). Material and Methods A total of 62 patients with newly diagnosed GBM who received postoperative irradiation (60 Gy in 6 weeks) with ART were prospectively evaluated. The initial clinical target volume (CTVi) was represented by a hyperintense signal abnormality on preoperative or postoperative T2- weighted MRI plus 10 mm. The initial planning target volume (PTVi) was CTVi plus a 5-mm margin. The leaf margin was 5 mm. The PTVi received 40 Gy at 2 Gy per fraction. For ART, contrast-enhanced MRI during radiotherapy (Mid-MRI) was taken at an irradiation dose of 34 Gy to 38 Gy. The boost clinical target volume (CTVb) was represented by the resection cavity and residual enhanced tumor on postoperative MRI plus 10 mm. In this study, two types of CTVb were created based on contrast- enhanced MRI before (postoperative state) and during radiotherapy (CTVb-Pre and CTVb-Mid, respectively). The boost planning target volume (PTVb) was CTVb plus 5 mm. Two types of boost plan (Pre-boost plan and Mid-boost plan) were also created. In actual radiotherapy, the PTVb- Mid received 20 Gy at 2 Gy per fraction. Post-radiotherapy MRI (Post-MRI) was taken on the last day of irradiation. The boost clinical target volume based on Post-MRI (CTVb-Post) was created in the same way as CTVb-Pre and CTVb-Mid, and PTVb-Post was created by adding a 5-mm margin to CTVb-Post. To investigate PTVb-Post coverage in the Pre- and Mid- boost plans, Post-MRI was fused with planning CT, and the dose-volume histograms of PTV-Post were compared. Additionally, the conformity indices (CIs) of the Pre-and Mid-boost plans were compared. CIs was defined as the ratio of the volume that received 95% of the prescribed dose to the PTV.

Figure: Kaplan-Meier analysis of survival by sex