INTRODUCTION: Brain metastasis velocity (BMV) is a prognostic metric that 
describes the recurrence rate of new brain metastases after initial treatment 
with radiosurgery (SRS). We have previously risk stratified patients into high, 
intermediate, and low-risk BMV groups, which correlates with overall survival 
(OS). We sought to externally validate BMV in a multi-institutional setting.
METHODS: Patients from nine academic centers were treated with upfront SRS; the 
validation cohort consisted of data from eight institutions not previously used 
to define BMV. Patients were classified by BMV into low (<4 BMV), intermediate 
(4-13 BMV), and high-risk groups (>13 BMV). Time-to-event outcomes were 
estimated using the Kaplan-Meier method. Cox proportional hazards methods were 
used to estimate the effect of BMV and salvage modality on OS.
RESULTS: Of 2829 patients, 2092 patients were included in the validation 
dataset. Of these, 921 (44.0%) experienced distant brain failure (DBF). Median 
OS from initial SRS was 11.2 mo. Median OS for BMV < 4, BMV 4-13, and BMV > 13 
were 12.5 mo, 7.0 mo, and 4.6 mo (p < 0.0001). After multivariate regression 
modeling, melanoma histology (β: 10.10, SE: 1.89, p < 0.0001) and number of 
initial brain metastases (β: 1.52, SE: 0.34, p < 0.0001) remained predictive of 
BMV (adjusted R2 = 0.06).
CONCLUSIONS: This multi-institutional dataset validates BMV as a predictor of OS 
following initial SRS. BMV is being utilized in upcoming multi-institutional 
randomized controlled trials as a stratification variable for salvage whole 
brain radiation versus salvage SRS after DBF.