Multi-institutional validation of brain metastasis velocity, a recently defined predictor of outcomes following stereotactic radiosurgery

•Brain metastasis velocity describes the recurrence rate of new brain metastases after initial treatment with radiosurgery.Brain metastasis velocity is calculated by dividing the number of new brain metastases after initial radiosurgery by the time in years since first radiosurgery.•Patients can be stratified into high, intermediate, and low risk velocity groups, which corresponds with overall survival.•The current study externally validates brain metastasis velocity as a prognosticator with over 700 patients from eight institutions.•Brain metastasis velocity is being employed in clinical trials as a tool to stratify patients for salvage whole brain radiation and radiosurgery.