RATIONALE: Androgens can cause the growth of prostate cancer cells. Drugs, such as leuprolide, goserelin, flutamide, or bicalutamide, may stop the adrenal glands from making androgens. Radiation therapy uses high-energy x-rays to damage tumor cells. Giving these drugs together with radiation therapy may kill more tumor cells.

PURPOSE: This phase II trial is studying how well androgen suppression with either leuprolide or goserelin and either flutamide or bicalutamide together with radiation therapy works in treating patients with prostate cancer.

OBJECTIVES:

• Determine the feasibility of androgen-suppression therapy combined with external-beam radiotherapy and boost brachytherapy (EBRT+BT) in patients with intermediate-risk localized prostate cancer.
• Determine the safety of EBRT+BT in these patients.
• Determine, in a preliminary manner, the efficacy of EBRT+BT in terms of rate of local recurrence at 5 years, time to prostate-specific antigen failure, and time to first rectal/bladder injury, in these patients.

OUTLINE: Patients receive either leuprolide intramuscularly or goserelin subcutaneously once every 12 weeks for a total of 24 weeks. Patients also receive either oral flutamide three times daily or oral bicalutamide once daily for 4 weeks.

Within 4 weeks after initiation of androgen-suppression therapy, patients undergo external-beam radiotherapy (EBRT) once daily, 5 days a week, for 5 weeks. At 2-4 weeks after completion of EBRT, patients undergo transrectal ultrasound-guided boost brachytherapy with implanted iodine I 125 or palladium Pd 103 seeds.

Patients are followed every 3 months for 2 years and then every 6 months for 4 years.

PROJECTED ACCRUAL: A total of 60 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the prostate

  • Must have one of the following prognostic factors:

    • Stage T1-2, N0; prostate-specific antigen (PSA) ≤ 10 ng/mL; and Gleason score > 6
    • Stage T1-2, N0; PSA > 10 ng/mL and < 20 ng/mL; and Gleason score ≤ 6
    • Stage T3a, N0; PSA ≤ 10 ng/mL; and Gleason score ≤ 6

• Prostate volume < 60 cc by transrectal ultrasound

• No distant or nodal metastases

  • No metastatic disease by bone scan, CT scan, or MRI

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• ECOG 0-2

Life expectancy:

• Not specified

Hematopoietic:

• Absolute neutrophil count ≥ 1,500/mm^3
• Platelet count ≥ 100,000/mm^3

Hepatic:

• Bilirubin ≤ 1.5 times upper limit of normal

Renal:

• Not specified

Other:

• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• No prior immunotherapy for prostate cancer

Chemotherapy:

• No prior chemotherapy for prostate cancer

Endocrine therapy:

• Prior androgen-suppression therapy for up to 4 weeks duration allowed if initiated within 4 weeks of study radiotherapy
• No other prior hormonal therapy

Radiotherapy:

• No prior radiotherapy for prostate cancer

Surgery:

• No prior surgery for prostate cancer
• No prior transurethral resection of the prostate

Other:

• No prior alternative therapy (e.g., PC-SPES) for prostate cancer