RADI-31. MULTI-INSTITUTIONAL VALIDATION OF BRAIN METASTASIS VELOCITY, A RECENTLY DEFINED PREDICTOR OF OUTCOMES FOLLOWING STEREOTACTIC RADIOSURGERY

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). Compared to initial salvage with WBRT, salvage SRS was associated with improved OS following DBF for BMV < 4 (p = 0.05), BMV 4–13 (p = 0.002) and BMV > 13 (p = 0.0001). 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 vs salvage SRS after DBF.