18F-Fluciclovine PET to Distinguish Tumor Progression From Radiation Necrosis

The purpose of this study is to evaluate whether 18F-fluciclovine PET/CT of the brain, is able to distinguish radiation necrosis from tumor progression in cases where MRI is inconclusive. 18F-fluciclovine is an FDA approved radioactive diagnostic agent and is injected into the participant and then taken up by cancer cells, which can then be visualized with a PET/CT scan. 18F-fluciclovine is FDA approved for the detection of recurrent prostate cancer, but is still investigational for the purposes of this study.