Post-operative hypofractionated stereotactic radiotherapy for brain metastases from lung and breast cancer in patients without prior WBRT: a retrospective dose escalation study.

This study investigated hypofractionated stereotactic radiotherapy (HSRT) for resected brain metastases and how the dose-fractionation affects local control (LC) and radionecrosis (RN). We retrospectively evaluated patients with brain metastases who were treated between 2010 and 2023. Post-operative HSRT was delivered in three or five fractions. The primary objective was to determine the effect of dose escalation and fractionation on LC. Secondary objectives included identifying factors associated with RN. Statistical analyses were conducted using Chi-square or Fisher's exact tests for categorical data and Mann-Whitney U tests for continuous variables (significance level: p < 0.05). After a median follow-up of 19 months, 34 patients out of 212 (16%) had local recurrence. A biologically effective dose (BED) > 28.8 Gy was associated with better LC (p = 0.002), but no benefit was found for a BED > 48 Gy. RN developed in 34 patients (16%). A prescription BED > 48 Gy was associated with an increased incidence of symptomatic RN (p = 0.002). For HSRT in three fractions, a CTV D99% ≥ 29 Gy significantly improved the LC (p = 0.04), and V30Gy, V23.1 Gy, and V18Gy were significantly associated with an increased risk of RN. The fractionation was not found to affect the LC or RN. This large, retrospective cohort study on post-operative HSRT indicates that a BED of 40.9-48 Gy (3 × 7,7 Gy or 5 × 6 Gy) to the planning target volume results in excellent LC while limiting the risk of RN. No difference in LC or RN was found for different fractionations.