Inclusion Criteria:  Age ≥ 18 years old. Subjects must have pathologically confirmed (by routine hematoxylin and eosin (H&E) staining) invasive adenocarcinoma of the prostate and must have been planning to undergo SBRT. Subjects must have one or more of the following: Clinical Stage T2b - T2c (AJCC 6th edition) tumor Gleason Score 7 as determined from a biopsy taken within 6 months of the baseline/screening visit Demonstrated blood PSA levels 10-20 ng/ml as measured during the Subject Enrollment/Baseline visit Subject or authorized representative was informed of the nature of the study and provided written informed consent, approved by the appropriate Institutional Review Board (IRB)/Ethics Committee (EC) of the respective clinical site.  Exclusion Criteria:  Prostate >80 cc documented within 3 months preceding the Screening/Baseline visit Clinical stage T3 or T4 (AJCC 6th edition) tumor Blood PSA level >20 ng/ml as measured during Subject Enrollment/Baseline visit Gleason Score ≥ 8 Subjects who had MRI evidence of posterior extracapsular extension (ECE) of the prostate cancer. Subjects who had metastatic disease, other ongoing cancers which were treated during the study or subjects for whom pelvic lymph node radiotherapy was planned. Subjects with any prior invasive malignancy (except non-melanomatous skin cancer) unless the subject had been disease free for a minimum of 3 years. History of prostatectomy, transurethral prostate surgery (e.g. TUNA, TUMT, TURP) if performed within 1 year prior to screening, other local prostate cancer therapy e.g., cryotherapy or brachytherapy) or previous pelvic irradiation at any time prior to screening. History of prior pelvic surgery requiring low anterior or abdominoperineal resections or rectal surgery. History of or active inflammatory bowel disease (IBD) such as Crohn's disease, ulcerative colitis, or irritable bowel disease. History of or current perirectal disease that may interfere with interpretation of study outcomes including anal or perianal diseases such as fistula. Bleeding hemorrhoids requiring medical intervention within the prior three months. Active bleeding disorder or a clinically significant coagulopathy defined as a Partial Thromboplastin Time (PTT) >35s or International Normalized Ratio (INR) > 1.4 or platelet count less than 100,000 per mm³. Note: Patients on anticoagulants may be included if the anticoagulant medication can be discontinued for index procedure. Active inflammatory or infectious process involving the perineum, gastrointestinal (GI) or urinary tract based on positive diagnosis or suspected diagnosis in the presence of fever >38⁰ C, WBC > 12,000/uL. Compromised immune system: WBC < 4000 /uL or > 12,000/uL or prior diagnoses for human immunodeficiency virus (HIV) (with a detectable viral load within the last 6 months)/acquired immunodeficiency syndrome (AIDS) or autoimmune disease. Contraindication for safe MRI, implants, or other conditions that would interfere with imaging required for the study (e.g., Non-MRI compatible pacemaker or metal that negatively impacts the MRI image at the discretion of the investigator). If a subject was enrolled in another investigational drug or device trial that had not completed the primary endpoint or that clinically interfered with this study. Unable to comply with the study requirements or follow-up schedule. Any condition the Investigator believed would interfere with the intent of the study or would make participation not in the best interest of the patient. Known iodine sensitivity or allergy