Safety and Feasibility of Stereotactic Radiosurgery for Patients with 15 or more Brain Metastases

Background Current standard of care treatment for patients with ≥15 brain metastases(BM) is whole brain radiation therapy(WBRT), despite poor neurocognitive outcomes. We analyzed our institutional experience of treating these patients with stereotactic radiosurgery(SRS), with the aim of evaluating safety, cognitive outcomes, and survival metrics. Methods Patients who received SRS for ≥15 BMs in 1-5 fractions from 2014-2022 were included. Cognitive outcomes were objectively evaluated using serial Patient-Reported Outcome Measurement Information System(PROMIS) scores. Kaplan-Meier method was used for survival analysis and log-rank test for intergroup comparisons. Results Overall, 118 patients underwent 124 courses of LINAC-based SRS. The median number of lesions treated per course was 20(range 15–94). Most patients received fractionated SRS to a dose of 24 Gy in 3 fractions(81.5%). At the time of SRS, 19.4% patients had received prior WBRT and 24.2% had received prior SRS. The rate of any grade radiation necrosis(RN) and ≥grade 3 RN were 15.3% and 3.2% respectively. When evaluating longitudinal PROMIS score trends, 25 of 31 patients had a stable/improved PROMIS score. Patients who did not receive prior brain RT had a longer median survival(7.4 months vs 4.6 months, p = .034). The 12m local control was 97.6%, while the cumulative incidence of distant intracranial failure, with death as a competing event, was 46%(95% CI 36%, 55%). One year freedom from neurological death, leptomeningeal disease, and salvage WBRT were 89%, 94.6% and 84% respectively. Conclusion We present here one of the largest studies evaluating SRS for patients with ≥15 BMs. SRS was safe, had favorable cognitive outcomes, and comparable survival outcomes to contemporary studies evaluating WBRT in this population. Treatment-naïve patients had a median survival of >6 months, long enough to benefit from cognitive sparing with SRS. Our study supports randomized studies comparing SRS and hippocampal avoidance WBRT approaches for these patients.