This prospective pilot study will assess the feasibility of rh PSMA 7.3 positron emission tomography/magnetic resonance imaging (PET/MRI) scans in detecting prostate cancer that may have come back (recurrent) in patients with increasing levels of prostate-specific antigen (PSA) following prostate surgery (biochemically recurrent). An increase in PSA levels alone does not tell the doctor where the cancer may be or how much cancer there may be. Imaging tests, like a bone scan, MRI, and/or computed tomography, are often performed to help the doctor learn where or how much cancer there is, and how best to treat the cancer. rhPSMA-7.3 is a radioactive tracer agent that when used with PET/MRI imaging may help diagnose and look for the spread of prostate cancer. Prostate-specific membrane antigen (PSMA) is a protein that is expressed in prostate cancer and this agent targets the PSMA molecule. Giving rh PSMA 7.3 during PET/MRI may help doctors better find where the cancer may be spreading and how much of it there is. The results of this trial may also guide in radiotherapy planning.

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.

Inclusion Criteria:

• Patient is male and aged > 18 years old
• History of localized adenocarcinoma of the prostate status post (s/p) radical prostatectomy
• An initial elevated PSA >= 0.2 followed by a subsequent confirmatory PSA >= 0.2 clinically suspicious for biochemically recurrent disease
• If the patients were previously taking androgen deprivation therapy (ADT), it should be discontinued at least 12 weeks prior to the study
• Treatment plan includes salvage radiation with or without hormones.
• Patient willing to provide signed informed consent and willing to comply with all required study schedule events, where safe and feasible
• Non-English speaking patients may be enrolled.

Exclusion Criteria:

• Patients with any medical condition or circumstance that the investigator believes may compromise the data collected or lead to a failure to fulfil the study requirements
• Patients who are planned to have an Iodinated contrast agent with computed tomography (CT) or gadolinium based contrast agent with MRI or other PET radiotracer < 24 hours prior to the PET scan
• Patients with contraindication to undergo MRI
• Patients with extreme claustrophobia
• Patients with prior allergy to MRI contrast agent
• Patients who are cognitively impaired