Patient description: The patient is a 63-year-old man presenting to the Emergency Department with a history of acute urinary retention in the past 2 days. Abdominopelvic CT scan revealed a large prostate and a bladder filled with urine. He is a candidate for urethral catheterization and TURP. Further evaluation revealed: Post-void residual: 71 mL Prostate volume (TRUS): 63 mL Prostate-specific antigen (PSA) level: 3.5 ng/mL His recent blood chemistry (3 days ago) was normal: Hgb: 13.6 g/dl WBC: 133000 /mm3 Plt: 370000 /ml PT: 12 second PTT: 34 second INR: 0.9 Creatinine: 0.5 mg/dl BUN: 10 mg/dl U/A: Color: yellow Appearance: cloudy PH: 5.3 Specific gravity: 1.010 Glc: 100 Nitrite: negative Ketone: none Leukocyte esterase: negative RBC: negative WBC: 2 WBCs/hpf U/C: negative

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Prostatic Neoplasms Prostate Cancer men with untreated prostate cancer 1. Patients must have histologically or cytologically confirmed prostate cancer. The outside pathology report is acceptable for study entry. Every effort will be made to acquire the outside pathology slides to be confirmed by the Laboratory of Pathology, NCI 2. Intermediate or high risk prostate cancer (clinical tumor stage T2b or higher, Gleason 7 or higher, or PSA greater than 10). Previously obtained MR imaging may be used for clinical T staging (extracapsular extension, seminal vesicle invasion). 3. No prior local therapy (prostatectomy, radiation, cryotherapy) or hormonal therapy for prostate cancer. 4. Age greater than or equal to18 years. 5. ECOG performance status less than or equal to 2 (Karnofsky greater than or equal to 60%). 6. Radiotherapy is planned as definitive therapy for prostate cancer. For patients not treated at NCI ROB patients must have a radiation oncologist who is willing to collaborate with the ROB and provide documentation of treatment. 7. Ability of subject to understand and the willingness to sign a written informed consent document. for men with presumed prostate cancer relapse 1. Patients must have a history of histologically or cytologically confirmed prostate cancer. The outside pathology report is acceptable for study entry. Every effort will be made to acquire the outside pathology slides to be confirmed by the Laboratory of Pathology, NCI 2. Age greater than or equal to 18 years. 3. ECOG performance status less than or equal to 2 (Karnofsky greater than or equal to 60%). 4. Radiotherapy (external beam irradiation alone or in combination with hormonal therapy and/or brachytherapy) was delivered as definitive therapy for prostate cancer and documentation is available. 5. Evidence of prostate cancer recurrence (biochemical relapse by the Phoenix definition, enlarging palpable prostatic abnormality, imaging evidence strongly suggestive of local failure) 6. Ability of subject to understand and the willingness to sign a written informed consent document  Patients unable to tolerate MRI (patients with pacemakers, cerebral aneurysm clips, shrapnel injuries, or other implantable electronic devices or metal not compatible with MRI). 2. Evidence of metastases (pelvic lymph node involvement is not an ). For patients with recurrent prostate cancer, oligometastatic disease (3 or lessfewer visible metastases) is not an criterion. 3. Patients with coagulopathies who are at increased risk for bleeding or on active anticoagulation therapy (platelets less than 100,000 per mm^3 or PT/PTT greater than 1.5 times the upper normal limit (UNL). Patients are eligible if the underlying cause is correctable. 4. Subjects weight exceeding MRI or radiation treatment table tolerance 5. Patients with active urinary tract infections 6. Patients with renal insufficiency with a GFR less than 30, due to the fact that they will not be able to undergo gadolinium enhanced MRI 7. Uncontrolled illness or comorbidity that in the judgment of the PI would preclude participation in the study 8. Hepatitis B or Hepatitis C active infection 9. HIV-positive patients are ineligible because HIV is known to increase radiation toxicity and may result in under-dosing or alterations in the treatment plan that would alter the likelihood of local recurrence. Appropriate studies will be undertaken in HIV positive patients when indicated