RATIONALE: Radiation therapy uses high-energy x-rays and other sources to damage tumor cells. Giving radiation therapy in different ways may kill more tumor cells.

PURPOSE: Phase II trial to study the effectiveness of external-beam radiation therapy followed by implanted radiation therapy in treating patients who have prostate cancer.

OBJECTIVES: I. Determine the acute and late grade 3-5 genitourinary and gastrointestinal toxic effects of external beam radiotherapy followed by permanent source brachytherapy using interstitial iodine I 125 seeds in patients with intermediate risk, clinically localized adenocarcinoma of the prostate. II. Determine the freedom from PSA failure, overall survival, disease specific survival, and local and/or distant clinical relapse rates in patients treated with this regimen.

OUTLINE: This is a multicenter study. Patients undergo external beam radiotherapy (EBRT) to the pelvis 5 days a week for 5 weeks. Permanent source brachytherapy comprised of ultrasound-guided implantation of iodine I 125 seeds into the prostate is performed 2-6 weeks after completion of EBRT. Patients are followed at 1, 3, 6, 9, and 12 months, then every 6 months for 2 years, and then annually thereafter.

PROJECTED ACCRUAL: A total of 110 patients will be accrued for this study within 1 year.

• Radiation: brachytherapy
• Radiation: iodine I 125
• Radiation: radiation therapy

• Lee WR, DeSilvio M, Lawton C, Gillin M, Morton G, Firat S, Baikadi M, Kuettel M, Greven K, Sandler H. A phase II study of external beam radiotherapy combined with permanent source brachytherapy for intermediate-risk, clinically localized adenocarcinoma of the prostate: preliminary results of RTOG P-0019. Int J Radiat Oncol Biol Phys. 2006 Mar 1;64(3):804-9. Epub 2005 Nov 14.
• Lee WR, Bae K, Lawton CA, Gillin MT, Morton G, Firat S, Baikadi M, Kuettel M, Greven K, Sandler H. A descriptive analysis of postimplant dosimetric parameters from Radiation Therapy Oncology Group P0019. Brachytherapy. 2006 Oct-Dec;5(4):239-43.
• Lee WR, Bae K, Lawton C, Gillin M, Morton G, Firat S, Baikadi M, Kuettel M, Greven K, Sandler H. Late toxicity and biochemical recurrence after external-beam radiotherapy combined with permanent-source prostate brachytherapy: analysis of Radiation Therapy Oncology Group study 0019. Cancer. 2007 Mar 5; [Epub ahead of print]

DISEASE CHARACTERISTICS: Histologically proven locally confined adenocarcinoma of the prostate Clinical stage T1c-T2b, NX or N0, M0 Gleason score 2-6 AND PSA greater than 10 ng/dL but no greater than 20 ng/dL OR Gleason score 7 AND PSA no greater than 20 ng/dL Prostate volume no greater than 60 mL by transrectal ultrasound prior to external beam radiotherapy American Urologic Association voiding symptoms score no greater than 18 No distant metastases

PATIENT CHARACTERISTICS: Age: Over 18 Performance status: Zubrod 0-1 Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Not specified Renal: Not specified Other: No hip prosthesis No other malignancy within the past 5 years except basal cell or squamous cell skin cancer No major medical or psychiatric illness that would preclude study Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy Endocrine therapy: Prior induction hormonal therapy allowed only if started no more than 6 months prior to study Radiotherapy: See Disease Characteristics No prior radiotherapy to pelvis Surgery: No prior transurethral resection of prostate No radical surgery for carcinoma of the prostate