An Investigational Scan (rh PSMA 7.3 PET/MRI) for the Detection of Recurrent Disease and Aid in Radiotherapy Planning in Biochemically Recurrent Prostate Cancer

PRIMARY OBJECTIVE: I. To evaluate the positive predictive value and detection rate of fluorine F 18 rhPSMA-7.3 (F-18 rhPSMA-7.3) positron emission tomography (PET)/magnetic resonance imaging (MRI) in detecting recurrent disease in prostate cancer patients with biochemical recurrence. SECONDARY OBJECTIVE: I. To determine the change in salvage radiation treatment plan after F-18 rhPSMA-7.3 PET/MRI imaging. EXPLORATORY OBJECTIVES: I. To assess the feasibility of utilizing the PSMA avid recurrent disease on PET/MRI as an alignment tool for MR guided radiotherapy (MR linear accelerator \[MR-LINAC\]). II. To assess the treatment response in those patients who demonstrate rhPSMA-7.3 avid disease on the first PET/MRI scan. OUTLINE: Patients receive F-18 rhPSMA-7.3 intravenously (IV) and after approximately 60 minutes of uptake time, will undergo PET/MRI over 60 minutes. Patients with evidence of F-18 rhPSMA-7.3 disease in the first PET/MRI scan undergo a second F-18 rhPSMA-7.3 PET/MRI at 6 months after the second dose of standard hormonal therapy. After completion of study treatment, patients are followed up within 7 days.