Brain [18F]-FES PET/CT in Patients With Estrogen-Receptor Positive Breast Cancer

The goal of this interventional study is to optimize the protocol of FES PET/CT in Estrogen Receptor positive Breast cancer patients with Brain metastases. Patients will undergo MRI of the brain and FDG PET/CT brain as part of standard of care for radiation treatment planning. An additional 18F-FES PET/CT brain scan will be completed before this standard of care radiation treatment. Patients will be followed prospectively with clinical and MRI assessments per standard-of-care for a total of 12 months. Study Population: Patients with ER-positive breast cancer with biopsy proven or suspected new or recurrent brain metastases (based on standard of care MRI) planned for radiation treatment of brain lesions.