Trial of Differential Margins in Single Isocenter Radiosurgery of Brain Metastases

Inclusion Criteria: 1. Stated willingness to comply with all study procedures and availability for the duration of the study 2. Male or female, aged 19 and older 3. Brain metastases diagnosis not requiring retreatment to the same tumor 4. For females of reproductive potential should undergo pregnancy testing as per UAB Radiation Oncology standard policies 5. Ability of subject or Legally Authorized Representative (LAR)) to understand and the willingness to sign a written informed consent document. Exclusion Criteria: 1. Current use of cytotoxic chemotherapy within 3 days of treatment. There are no restrictions on the use of immunotherapy during treatment. TKIs known to be radiation sensitizers such as BRAF should be held at least 24 hours prior to treatment. 2. Inability to have MRI imaging 3. Pregnancy 4. Treatment with another investigational drug 14 days of enrollment 5. Radiosurgery planned for post-operative adjuvant cavity only. Patients with any gross residual after surgery are eligible. Patients with at least one intact metastasis may enroll but adjuvant cavity will not be evaluable. 6. At the time of Radiation Oncology consultation more than twenty targets are identified. Note that it is common that a few additional metastases may be identified during the treatment planning or peer review processes. More than twenty targets may be included if this number is found after the initial clinical review of the treatment planning MRI. 7. Tumor maximal diameter \> 4 cm. 8. Prior SBRT or SRS to a lesion planned for retreatment. Note that patients with prior whole brain radiation alone are eligible. 9. Patients with diffuse leptomeningeal tumor are not eligible. Patients with a focal dural or pachymeningeal tumor are eligible if other intra-axial tumors are planned to be treated. Similar to postoperative cavities, the pachymeningeal tumor deposit will be treated but not evaluable for the assessment of local control or toxicity. INCLUSION OF VULNERABLE PARTICIPANTS Vulnerable populations as defined by the NIH including children, prisoners, and adult subjects who lack capacity to consent to research participation are not eligible.