Observation of Outcomes and Side Effects of Cesium-131 in Combination With External Beam Radiation for the Treatment of Intermediate to High Risk Prostate Cancer

Inclusion Criteria: * Histologically confirmed adenocarcinoma of the prostate * Clinical stage T1c - T2c (AJCC 6th Edition), NX/N0, M0 * Karnofsky Performance Score of 90 to 100 * Greater than or equal to 18 years of age * Prostate volumes by TRUS ≤ 60 cc * I-PSS score \< 15 (alpha blockers allowed) * Signed study-specific informed consent form prior to study entry Intermediate Risk prostate cancer as determined by the following: * Gleason sum of 7; PSA less than 10.1 ng/ml; Stage T2a or less * Gleason sum 6 or less; PSA \>10.0 and \< 20.1ng/ml; Stage T2a or less * Gleason sum 6 or less; PSA \< 10.1; Stage T2b High risk prostate cancer as determined by the following: * Any Gleason Sum; PSA greater than 20 ng/ml; Stage T2c or less * Gleason Sum \> 7; Any PSA; Stage T2c or less * Any Gleason Sum; Any PSA; Stage T2c * Any two or three intermediate risk factor Exclusion Criteria: * Lymph node involvement (N1) * Evidence of distant metastases (M1) * Any hormonal blockade or therapy that: * Has persisted for more than 6 months by time of protocol screening; OR * Is ongoing within 3 months of study enrollment * Radical surgery for carcinoma of the prostate * Prior pelvic radiation * Previous or concurrent cancers other than basal, in situ, or squamous cell skin cancers unless disease-free for ≥ 5 years * Major medical or psychiatric illness, which in the investigator's opinion, would prevent completion of treatment and would interfere with follow-up * Hip prosthesis * Inability or refusal to provide informed consent