Phase I Compare OS in Post-CyberKnife Radiosurgery Tx in 1-3 VS 4 or More Brain Metastases

This is registry-based cohort study of patients with brain metastases treated at Stanford University Medical Center (SUMC) with CyberKnife radiosurgery (CK RS). It has two components: (1) a retrospective follow-up of patients treated since 2006, and (2) the accrual of a new cohort of patients treated over a 5-year period from January 15, 2013 to December 31, 2017 and followed for at least one year thereafter. The primary aim of this study is to estimate the effect of the number of brain tumor metastases on survival after adjusting for known risk factors for mortality.