INCLUSION CRITERIA  Adenocarcinoma of the prostate treated with radical prostatectomy (any type of radical prostatectomy is permitted including retropubic, perineal, laparoscopic or robotically assisted; there is no time limit for the date of radical prostatectomy). Pathologic T3N0/Nx disease or pathologic T2N0/Nx disease, with or without a positive prostatectomy surgical margin Post-radical prostatectomy PSA of ≥ 0.1 - < 2.0 ng/mL. Clinical local relapse assessed by Magnetic Resonance Imaging (MRI) of the pelvis ECOG performance status of 0-1 No distant metastases at restaging (in case of biochemical failure), within 60 days prior to registration Patients can be on androgen deprivation therapy Ability to understand and willingness to sign a study-specific informed consent prior to study entry  EXCLUSION CRITERIA  N1 and or M1 patients Prior radiation of any kind to the prostate gland or pelvis Prior brachytherapy is not allowed History of inflammatory colitis or other active severe comorbidities Patients who are on immunosuppressant medication