Internal Radiation Therapy in Treating Patients With Prostate Cancer

DISEASE CHARACTERISTICS: Inclusion criteria: * Intermediate-risk adenocarcinoma of the prostate, defined by 1of the following criteria: * PSA 10-20 ng/mL * Gleason score ≥ 7 * Stage ≥ T2b AND \< T3 * Less than 20% risk of seminal vesicle involvement or lymph node involved based upon the Kattan nomogram (pre-treatment risk with IMRT) * Prostate size \< 60 cc by MRI or CT imaging * International Prostate Symptom Score Index ≤ 15 Exclusion criteria: * Evidence of definitive extracapsular extension/seminal vesicle invasion or pelvic adenopathy by MRI (endorectal coil) and DRE (digital rectal examination) * Suspected extracapsular disease will not be considered an exclusion criteria * PSA \> 20 ng/mL * Presence of distant metastases PATIENT CHARACTERISTICS: * WBC ≥ 3,500/mm³ * Platelet count ≥ 75,000/mm³ * Hemoglobin ≥ 10 g/dL * Creatinine ≤ 1.5 mg/dL * Liver function tests ≤ 1.5 times normal * INR ≤ 2.5 * Able to complete quality of life questionnaires * Able to give informed consent * No active perineal infections * No history of urethral stricture * No prior history of pelvic malignancy * No prior history of lymphoma disease, ulcerative colitis, or anal fissures * No contraindications to general anesthesia * No pacemaker PRIOR CONCURRENT THERAPY: * No prior transurethral resection of the prostate * No prior pelvic radiotherapy * No prior treatment for prostate cancer except for hormone therapy