A Study of MRI-guided High-dose Radiation Therapy in Prostate Cancer

Inclusion Criteria: * Intermediate-risk prostate cancer patients will be eligible for this study. Risk groups will be assigned as per NCCN guidelines. Intermediate-risk patients will be defined as: * PSA 10-20 ng/ml or * Gleason score = 7 or * Clinical stage T2b/T2c or * Additionally, patients will be required to meet all of the following criteria: * Age ≥ 18 * Karnofsky Performance Status (KPS) ≥ 80 (Appendix 1) * Prostate size ≤ 80 cc * Presence of a T2-visible prostatic lesion with maximum dimension of ≥ 0.5 cm and no more than one additional disease focus * MRI findings: Lesion may contact the capsular edge, possible extracapsular extension (ECE) permitted * International Prostate Symptom Score ≤ 15 * Satisfy all MRI screening criteria and be willing to fill out the standard MRI screening form Exclusion Criteria: Patient will be excluded if they meet any one of the following criteria: * Gleason score \>7 * PSA \>20 * Prior or concurrent androgen deprivation therapy for prostate cancer MRI findings: suspicious for/probable ECE * MRI findings: \>2 disease foci identifiable * Evidence of metastatic disease on bone scan or MRI/CT * MRI ineligibility due to: the presence of a cardiac pacemaker, defibrillator, or other implanted metallic or electronic device which is considered MR unsafe; severe claustrophobia; inability to lie flat for the duration of the study; etc. * Metallic implant or device in the pelvis that might distort the local magnetic field and compromise quality of mp-MRI * Lateral pelvic separation greater than 50 cm and/or anterior-posterior separation greater than 35 cm which are incompatible with MRCAT reconstruction * Contra-indications to receiving gadolinium contrast * KPS \< 80 * Pelvic or prostate MRI or CT (MRI preferred) evidence of radiographic T3, T4, or N1 disease * Prior history of transurethral resection of the prostate * Prior history of urethral stricture * Prior history of pelvic irradiation * History of inflammatory bowel disease * Unable to give informed consent * Unable to complete quality of life questionnaires * Abnormal complete blood count, including any of the following: * Platelet count less than 75,000/ml * Hb level less than 10 gm/dl * WBC less than 3.5/ml * Abnormal renal function tests (creatinine \> 1.5)