Incorporating MR Imaging Into Prostate Radiotherapy Treatment Planning

Inclusion Criteria: * Participants must have histologically confirmed prostate cancer. * PSA level and prostate biopsy must be reviewed at Brigham and Women's Hospital or the Dana Farber Cancer Institute and should support a diagnosis of stage I-III prostate adenocarcinoma. * Candidates with PSA greater than 20, digital rectal exam consistent with disease outside the prostate (clinical T3/T4 disease), or Gleason score 8 or greater, should have a bone scan and diagnostic pelvic CT or MRI to exclude metastatic disease. * Prostate biopsy, serum PSA measurement, and any indicated diagnostic imaging studies must be performed within 60 days of the date of registration. * Participants should not have had prior curative local treatment for prostate cancer, including no radiotherapy or prostatectomy. A maximum 90 days of systemic androgen deprivation therapy prior to registration is allowed. * Participation is limited to adult patients, age 18 years or older. * ECOG performance status ≥2 (Karnofsky ≥60%) * Life expectancy of greater than 10 years. * Able to tolerate an MRI examination. * Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: * Participants with known or suspected metastatic (stage IV) prostate cancer. * Participants with an implanted device, prosthesis, or any other foreign body with ferromagnetic properties that would make them ineligible to undergo MRI examination. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.