In this research study, the investigators are trying to determine if there are measurable changes in prostate MRI that will help predict those who will or will not respond to Androgen Deprivation Therapy (ADT) and External Beam Radiation Therapy (EBRT) The first baseline prostate MRI prior to the start of treatment is standard of care. The participant's ADT/EBRT treatment is also standard of care, as advised by their doctor. It is the 3 follow up prostate MRIs during ADT/EBRT treatment, and 4 follow up serum PSA levels that are part of this research study.

If the participant chooses to take part in this research study, the participant will have 3 follow up prostate MRIs during a 6 month time period, while the participant is having their ADT/EBRT treatment. These follow-up prostate MRIs will use a standard imaging protocol without the use of an endorectal coil. The participant will also have a total of 4 blood samples to measure serum PSA. 1-2 mls (just less than ½ teaspoon) will be taken for each sample.

Research Study Plan

• Baseline Visit (routine standard of care screening visit): PSA blood test and prostate MRI
• Visit 1 (8 weeks after starting ADT): PSA blood test and prostate MRI
• Visit 2 (6 weeks after starting EBRT): PSA blood test and prostate MRI
• Visit 3 (on last day of EBRT): PSA blood test
• Visit 4 (6 months after starting ADT): PSA blood test and prostate MRI

Planned Follow-up: The investigator would like to keep track of the participant's prostate cancer status while they continue to see their doctor at DFCI. The investigators would like to do this by collecting the following data from the participant's medical records, to look at long-term outcome of their ADT/EBRT treatment.

• PSA values
• Clinical results of your treatment. The investigator will not contact the participant to obtain this information.

Inclusion Criteria:

• Adult males with unfavorable intermediate- to high-risk localized disease, defined as having one of the following three categories, Clinical or radiographic T2b-T4 primary tumor or Gleason score 7-10 in any core, or PSA ≥ 10 prior to initiation of therapy
• Patients are deemed suitable for therapy with ADT and EBRT.
• Subjects must to able to provide informed written consent prior to study entry.

Exclusion Criteria:

• The standard exclusion criteria for MRI exams will apply which include patients with pacemakers, non-compatible intra-cranial vascular clips, inner ear implants, and severe claustrophobia.
• Patients who because of age, general medical or psychiatric condition, or physiologic status unrelated to the presence of prostate cancer are unlikely to be candidates for repeat MRIs, or cannot give valid informed consent.
• Patients unwilling or unable to undergo the multiparametric MRI exam (non-endorectal coil).
• Patients with a history of allergic reaction to latex or Gadolinium containing intravenous contrast agents.
• Individuals with renal disease or other contraindications to gadolinium will be excluded. The BWH standard MRI contrast screening criteria will be used to establish renal status.
• Patients who have had prior prostatectomy or prior androgen therapy.
• Patients with hip implant or any other metallic implant or device that results in significant distortion of the local magnetic field and compromise of the quality of the multiparametric MRI data.

During and immediately after the MRIs.

Adverse events included any serious events related to the MRI exam. Expected adverse events from MRI are not serious and include claustrophobia while in the MRI magnet, a warming sensation while in the MRI magnet, or infiltration of intravenous contrast in the subcutaneous tissues at the time of its administration.