More than Just the Number of Brain Metastases: Evaluating the Impact of Brain Metastasis Location and Relative Volume on Overall Survival After Stereotactic Radiosurgery.

OBJECTIVE: Most evidence describing outcomes of patients with brain metastases is based on number of brain metastases, rather than location or volume. We evaluated the impact of tumor location and relative volume on overall survival (OS) among a large cohort of patients treated with stereotactic radiosurgery. METHODS: Clinical, radiographic, and dosimetric data were collected on patients treated with first (if multiple) stereotactic radiosurgery for brain metastases. Multivariate analyses were performed to investigate the impact of brain metastasis relative location and volume on OS after stereotactic radiosurgery. RESULTS: Analysis included 300 patients with 817 tumors (116 patients with single brain metastasis). The most common tumor locations were supratentorial (75% of tumors), cerebellar (19%), and brainstem (5%). Median tumor volume was 0.4 mL (range, 0.003-65.0 mL). Tumor-specific factors associated with inferior OS included brainstem location versus both supratentorial and cerebellum locations for particular assumed values of cube root tumor volume (P < 0.001 for each) and increasing total supratentorial tumor volume (P = 0.004). Patients with supratentorial tumors and cerebellar tumors demonstrated similar OS, and cube root total tumor volume within the cerebellum and brainstem did not predict for OS. CONCLUSIONS: The presence of brainstem metastases and cumulative supratentorial tumor volume are adverse features that result in inferior survival. These results can be used to inform patient prognosis and future clinical trial design.