Radiation necrosis and therapeutic outcomes in patients treated with linear accelerator‐based hypofractionated stereotactic radiosurgery for intact intracranial metastases

Introduction Balancing disease control and treatment‐related toxicities can be challenging when treating higher‐risk brain metastases (BMs) that are larger in size or eloquent anatomical locations. Hypofractionated stereotactic radiosurgery (hfSRS) is expected to offer superior or equal efficacy with lower toxicity profile compared with single‐fraction SRS (sfSRS). We report the efficacy and toxicity profiles of hfSRS in a consecutive cohort of patients to support this predicted benefit from hfSRS for high‐risk BMs. Methods We retrospectively analysed 185 consecutive individual lesions from 152 patients with intact BMs treated with hfSRS between 1 July 2016 and 31 October 2019 and followed up to 30 April 2022 with serial brain magnetic resonance imaging (MRI). The primary endpoint was the event of radiation necrosis (RN). Local control (LC) rate and distant brain failure (DBF) were reported as secondary outcomes. Kaplan–Meier method was used to report the cumulative incidence of RN and overall survival and the incidence of DBF. Potential risk factors for RN were assessed using univariable Cox regression analysis. Results The median follow‐up was 38.0 months, and the median survival post‐SRS was 9.5 months. The cumulative incidence rate of RN was 13.2% (95% CI: 7.0–24.7%), and 18.1% of patients with confirmed RN were symptomatic. Higher mean dose delivered to planning target volume (PTV) (HR 1.22, 95% CI: 1.05–1.42, P = 0.01), higher mean BED10 (biological equivalent dose assuming a tissue α/β ratio of 10) (HR 1.12, 95% CI: 1.04–1.2, P