A Study of Stereotactic Radiosurgery (SRS) in People With Brain Cancer Having Tumor Resection Surgery

Inclusion Criteria: * Histologically or cytologically confirmed breast cancer, non-small cell lung cancer, melanoma, or gastrointestinal cancer. In malignancies for which tissue confirmation is not standard diagnostic practice (for example, hepatocellular carcinoma diagnosed by characteristic imaging), radiographic diagnosis consistent with standard of care is acceptable. In all cases, the intracranial lesion planned for resection undergoes pathologic examination as part of protocol-directed surgery. * At least one intact brain metastasis is planned for surgical resection that has not previously received stereotactic radiosurgery or other focal radiotherapy, measuring 6 cm or less in diameter. * No evidence of leptomeningeal disease based on clinical symptoms, MRI imaging of the brain or spinal cord, and/or lumbar puncture cytologic analysis. * No prior SRS to the index BM planned for surgical resection. Prior SRS to non- index lesions is permitted, with approval from the principal investigator. The interval since prior cranial radiotherapy will be recorded. All clinically significant toxicities from prior radiotherapy must have resolved to grade 1 or lower (CTCAE); patients with unresolved symptomatic (grade 2 or higher) radiation necrosis, treatment-related enhancing treatment effect, or clinically significant cerebral edema attributable to prior cranial radiation are not eligible. * No prior therapeutic craniotomy or craniectomy with biopsy. * Age ≥ 18 * Karnofsky Performance Status (KPS) of ≥ 70 and anticipated survival of \>1 year * Ability to undergo contrast-enhanced MRI brain Exclusion Criteria: * Pregnant and/or breastfeeding * Prior whole brain radiotherapy. * Neurologic instability despite medical management, such that either the treating team or study investigators feel that urgent craniotomy without awaiting SRS is indicated. * Judgment by the principal investigator that the patient should not participate in the study if the patient is unlikely to comply with study procedures, restrictions, and requirements.