Stereotactic Radiosurgery or Whole-Brain Radiation Therapy in Treating Patients With Brain Metastases That Have Been Removed By Surgery

Pre-registration Inclusion Criteria: 1. Number of Brain Metastases - Four or fewer brain metastases (as defined on the pre-operative MRI or CT brain scan) and status post resection of one of the lesions. 2. Non-CNS Primary Site - Pathology from the resected brain metastasis must be consistent with a non-central nervous system primary site. Note: Patients with or without active disease outside the nervous system are eligible (including patients with unknown primaries), as long as the pathology from the brain is consistent with a non-central nervous system primary site. 3. Size of Metastases - Any unresected lesions must measure \< 3.0 cm in maximal extent on the contrasted MRI or CT brain scan obtained ≤ 35 days prior to pre-registration. The unresected lesions will be treated with SRS as outlined in the treatment section of the protocol. Note: The metastases size restriction does not apply to the resected brain metastasis; with resected brain metastases only surgical cavity size determines eligibility. 4. Size of Resection Cavity - Resection cavity must measure \<5.0 cm in maximal extent on the post-operative MRI or CT brain scan obtained ≤35 days prior to pre-registration. Note: It is permissible for the resection of a dominant brain metastasis to include a smaller "satellite" metastasis as long as the single resection cavity is less than the maximum size requirements. 5. Tumor Staging Procedures - All standard tumor-staging procedures necessary to define baseline extra cranial disease status completed ≤42 days prior to pre-registration. 6. Treatment with Gamma Knife or Radiosurgery - Able to be treated with either a gamma knife or a linear accelerator-based radiosurgery system. 7. Age ≥ 18 years 8. Neurocognitive Testing - Willing and able to complete neurocognitive testing without assistance from family and companions. Note: Because neurocognitive testing is one of the primary goals of this study, patients must be able to utilize English language booklets (and/or French booklets if enrolled in Canada). 9. Quality of Life (QOL) Questionnaires - Willing and able to complete QOL by themselves or with assistance 10. ECOG Performance Status - ECOG Performance Status (PS) 0, 1, or 2. 11. SRS Credentialed by IROC Houston Quality Assurance - The site's SRS facility is IROC Houston Quality Assurance approved. 12. Neurocognitive Testing Credentialing - The site study team member performing neurocognitive testing of patients must have credentialing confirming completion of the neurocognitive testing training of the protocol. 13. Written Informed Consent - Provide written informed consent 14. Mandatory Samples for Correlative Tests - Willing to provide mandatory blood and urine samples for correlative research purposes. Pre-registration Exclusion Criteria: 1. Pregnancy, Nursing and Contraception - pregnant women, nursing women and men or women of childbearing potential who are unwilling to employ adequate contraception throughout the study and for men for up to 3 months after completing treatment. 2. Prior Cranial Radiation Therapy 3. MRI or CT Scans - Inability to complete a MRI or CT scan with contrast of the head. 4. Gadolinium Allergy - Known allergy to gadolinium. 5. Cytotoxic Chemotherapy - Planned cytotoxic chemotherapy during the SRS or WBRT. 6. Other Tumor Types - Primary germ cell tumor, small cell carcinoma, or lymphoma 7. Leptomeningeal Metastasis - Widespread definitive leptomeningeal metastasis 8. Location of Brain Metastasis - A brain metastasis that is located ≤ 5 mm of the optic chiasm or within the brainstem. Randomization Inclusion Criteria: 1. Number of Unresected Lesions - Post-operative MRI or CT scan confirmed zero, one, two or three unresected lesions. 1.1 Each unresected lesion must measure ≤ 3.0 cm in maximal extent on the contrasted post-operative MRI or CT brain scan. 1.2 Note: The pre-registration, post-operative, brain scan may be used for the randomization scan if obtained ≤ 28 days prior to randomization. 1.3 Note: If there are no unresected brain metastases (i.e., all brain metastases have been resected), a post-operative CT brain scan may be used if obtained ≤ 28 days prior to randomization. 2. Size of Resection Cavity - Post-operative MRI or CT scan confirms resection cavity measures \< 5.0 cm in maximal extent. 2.1 Note: The pre-registration, post-operative brain scan may be used for the randomization scan if obtained ≤ 28 days prior to randomization. 2.2 Note: If there are no unresected brain metastases (i.e., all brain metastases have been resected), a post-operative CT brain scan may be used if obtained ≤28 days prior to randomization. 3. Urine or Serum Pregnancy Test - Negative urine or serum pregnancy test done ≤ 7 days prior to randomization, for women of child bearing potential only. Randomization Exclusion Criteria: none