High-Dose-Rate Brachytherapy

Inclusion Criteria: * Prior enrollment of UHN 05-0641-C or UHN 12-5015-C (Arm 1) * Histological evidence of recurrent prostate adenocarcinoma (Arm 1) * PSA doubling time \> 6 months (Arm 1) * Intermediate and High-risk localized prostate cancer (\>T1 or PSA\>10 or Gleason \> 6) (Arm 2) * Planned for EBRT + HDR boost (+/- hormone therapy) (Arm 2) * ECOG 0 or 1 * Age \> 18 years * Informed consent: All patients must sign a document of informed consent indicating their understanding of the investigational nature and risks of the study before any protocol related studies are performed. Exclusion Criteria: * Radiological evidence of regional or distant metastases * Contraindications to MRI (Patient weight as per MRI Technologist's discretion, Patients with pacemakers, cerebral aneurysm clips, shrapnel injury, or implantable electronic devices not compatible with MRI) * Bleeding diathesis and anti-coagulative therapy that cannot be temporarily ceased during brachytherapy * Previous prostate brachytherapy * Active hormonal therapy at time of brachytherapy (Arm 1) * Previous pelvic radiotherapy (Arm 2) * Contraindications to endorectal coil, surgically absent rectum, severe hemorrhoids or colorectal surgery. * Latex Allergy * Contraindications to conscious sedation, local anesthesia, or spinal/epidural anesthesia. * IPSS \>18 * Large TURP defect * TURP within the past 6 months * Prostate gland size \>80cc (Arm 2, whole gland HDR patients only) * History of Ulcerative Colitis and SLE (except for patients where the clinician determines benefit outweighs the risk of radiation) * Other medical conditions deemed by the PI to make patient ineligible for MRI-guided Prostate HDR brachytherapy.