Significant correlation between gross tumor volume (GTV) D98% and local control in multifraction stereotactic radiotherapy (MF-SRT) for unresected brain metastases

Background Stereotactic radiotherapy (SRT) should be applied with a biologically effective dose an ?/? of 12 (BED12) ? 40 Gy to reach 1-year local control (LC) 70%. The aims this retrospective study were report series 81 unresected large brain metastases treated Linac-based multifraction SRT according the ICRU 91 and identify predictive factors associated LC. Methods Included in first (BM) consecutively volumetric modulated arc therapy (VMAT) from 2017 2019. prescribed was 33 for GTV 23.1 (70% isodose line) PTV 3 fractions (3f). Mean BM largest diameter 25.1 mm 7.2 cc respectively. follow-up 10.2 months. Results LC 79.7% 69.7% at 1 2 years Significant D98% (HR = 0.84, CI 95% 0.75–0.95, p 0.004) adenocarcinoma as histological type 0.29, 0.09–0.96, 0.042) univariate multivariate analysis. A threshold 29 significantly correlated (1-year 91.9% vs 69.6% < (p 0.030)), corresponding BED12 52.4 Gy. No tumor progression observed 53.4 Gy, 20 /1f 29.4 3f. Median OS 15 Symptomatic radionecrosis occurred 4.9% cases. Conclusion is strong reproducible significant factor SRT. Dose prescription lead 98% 52.4–53.4 improve LC, respectively 19.7–20 Gy/1f 29–29.4 Gy/3f.