Assess Use of 18F-Fluciclovine for Patients With Large Brain Metastases Treated With Staged Stereotactic Radiosurgery

Inclusion Criteria: 1. Male or female, age ≥18 years 2. Performance status, Eastern Cooperative Oncology Group 0-2 3. Confirmed diagnosis of brain metastases with at least one untreated lesion \>2 cm in maximum diameter 4. Plan for SSRS per the treating team 5. For women of childbearing potential, a negative serum pregnancy test within 14 days of registration is required 6. For females of reproductive potential: use of highly effective contraception for at least 4 weeks prior to screening and agreement to use such a method during study participation and for an additional 1 week after post-treatment 18F-fluciclovine positron emission tomography/computerized tomography Exclusion Criteria: 1. Prior anaphylactic reaction to 18F-fluciclovine 2. Evidence of leptomeningeal disease 3. Prior whole-brain radiation therapy 4. Contraindication to MRI (e.g., due to safety reasons, such as presence of a pacemaker) 5. Females pregnant at the expected time of 18F-fluciclovine administration 6. Females who are expecting to be breastfeeding at the time of 18F-fluciclovine and unwilling to stop breast-feeding for 24 hours. Temporary cessation of breastfeeding 24 hours after the time of imaging is allowed 7. Major medical illness or psychiatric/cognitive impairments, which in the investigator's opinion, will prevent completion of protocol therapy and/or preclude informed consent