The structure of the current study provides a unique opportunity to explore various dosimetric SRS parameters in the setting of multiple brain metastases. Dose-volume criteria for SRS have been established in a prospective RTOG 90-05 dose-finding study and subsequently validated in RTOG 95-08, a randomized controlled trial of WBRT±SRS in patients with 1-3 brain metastases. Several single-institution series as well as multi-institutional retrospective analyses support the use of single-dose SRS for treatment of brain metastases; however, the dose-volume criteria and prescription guidelines are not known in the setting of ≥5 brain metastases where dose interaction among different lesion targets are much more likely. These interactions can potentially lead to increased rates of radiation necrosis, and if the SRS doses are arbitrarily reduced because of such concerns, then to a potentially decreased local control rates. These parameters will be closely tracked in this study with the aim of establishing an evidence-based dosimetric guidelines for radiosurgical treatment of multiple (≥5) brain metastases.