Inclusion Criteria:

          -  Adenocarcinoma of the prostate, post radical-prostatectomy

          -  Detectable prostate-specific antigen (PSA)

          -  Eastern Cooperative Oncology Group (ECOG)/Zubrod performance status of 0-2

          -  No definitive findings for skeletal metastasis on technetium 99-m methyl diphosphonate
             (MDP) or F-18 PET bone scan

          -  No definitive findings of systemic (extrapelvic) metastasis on CT and/or magnetic
             resonance (MR) scan of abdomen and pelvis

          -  Willingness to undergo pelvic radiotherapy

        Exclusion Criteria:

          -  Contraindications to radiotherapy (including active inflammatory bowel disease or
             prior pelvic radiotherapy)

          -  Inability to undergo fluciclovine or Ga-PSMA PET-CT

          -  Definitive findings of systemic metastasis on conventional imaging or biopsy

          -  Prior invasive malignancy (except non-melanomatous skin cancer) unless disease free
             for a minimum of 3 years

          -  Severe acute co-morbidity, defined as follows:

               -  Unstable angina and/or congestive heart failure requiring hospitalization in the
                  last 3 months

               -  Transmural myocardial infarction within the last 6 months

               -  Acute bacterial or fungal infection requiring intravenous antibiotics at the time
                  of registration

               -  Chronic Obstructive Pulmonary Disease exacerbation or other respiratory illness
                  requiring hospitalization or precluding study therapy at the time of registration

               -  Acquired immune deficiency syndrome (AIDS) based upon current Center for Disease
                  Control (CDC) definition; note, however, that human immunodeficiency virus (HIV)
                  testing is not required for entry into this protocol. The need to exclude
                  patients with AIDS from this protocol is necessary because the treatments
                  involved in this protocol may be significantly immunosuppressive.
                  Protocol-specific requirements may also exclude immunocompromised patients