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

OBJECTIVES: * Compare the 5-year freedom from progression in patients with intermediate-risk prostate cancer treated with interstitial brachytherapy with or without external beam radiotherapy (EBRT). * Compare biochemical (i.e., prostate-specific antigen) failure, biochemical failure by the Phoenix definition, disease-specific survival, local progression, and distant metastases in patients treated with these regimens. * Compare morbidity and quality of life of patients treated with these regimens. * Determine the feasibility of collecting Medicare data in a large Radiation Therapy Oncology Group (RTOG) prostate cancer clinical trial for cost effectiveness and cost utility analysis of combined treatment with interstitial brachytherapy and EBRT. * Prospectively collect diagnostic biopsy samples from these patients for future biomarker analyses. OUTLINE: This is a randomized, multicenter study. Patients are stratified according to disease stage (T1c vs T2a or T2b), Gleason score (≤ 6 vs 7), prostate-specific antigen (\< 10 ng/mL vs 10-20 ng/mL), and prior neoadjuvant hormonal therapy (yes vs no). Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients undergo external beam radiotherapy 5 days a week for 5 weeks. Within 2-4 weeks of radiotherapy, patients undergo interstitial brachytherapy with iodine I 125 or palladium Pd 103 seeds. * Arm II: Patients undergo interstitial brachytherapy only, as in arm I. Quality of life is assessed at baseline, at 4, 12, and 24 months, and then annually for 3 years. After completion of study treatment, patients are followed at 3-5 weeks, at 4, 6, 9, and 12 months, every 6 months for 4 years, and then annually thereafter.