Interstitial Brachytherapy With or Without External-Beam Radiation Therapy in Treating Patients With Prostate Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed adenocarcinoma of the prostate * T1c-T2b, N0, M0 * Intermediate-risk disease, as defined by 1 of the following: * Gleason score \< 7 AND prostate-specific antigen (PSA) 10-20 ng/mL * Gleason score 7 AND PSA \< 10 ng/mL * No evidence of distant metastases * Prostate volume ≤ 60 cc by transrectal ultrasonography * American Urological Association voiding symptom score no greater than 15 (alpha blockers allowed) PATIENT CHARACTERISTICS: Age * 18 and over Performance status * Zubrod 0-1 Life expectancy * Not specified Hematopoietic * Not specified Hepatic * Not specified Renal * Not specified Other * Patients must use effective contraception * No other malignancy within the past 5 years except basal cell or squamous cell skin cancer or carcinoma in situ at any other site * No major medical or psychiatric illness that would preclude study therapy * No hip prosthesis PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * No prior chemotherapy Endocrine therapy * Prior neoadjuvant hormonal therapy allowed provided the following are true: * Therapy was initiated within 2-6 months of study enrollment * Therapy was no more than 6 months in duration * Use of 5-alpha reductase inhibitors (e.g., finasteride) is discontinued before registration * No concurrent hormonal therapy Radiotherapy * No prior pelvic radiotherapy Surgery * No prior radical surgery for prostate cancer * No …