This is randomized controlled study of neurocognitive outcomes in patients with five or more brain metastases treated with stereotactic radiosurgery (SRS), specifically the Gamma Knife (GK) system, or whole-brain radiation therapy (WBRT). The goal of the study is to enroll 120 patients with at least five (≥5) newly-diagnosed brain metastases from non-melanoma, except melanoma patients with BRAF V600E B-Raf protein mutation, primary cancers with the largest intracranial tumor volume ≤10 cc, ≤15 cc total tumor volume, absence of leptomeningeal disease on MRI, and Karnofsky performance status (KPS) score ≥70 (unless due to intracranial disease), and KPS expected to improve to ≥70 with treatment.