RATIONALE: Stereotactic body radiation therapy may be able to send x-rays directly to the tumor and cause less damage to normal tissue.

PURPOSE: This phase I/II trial is studying the side effects and best dose of stereotactic body radiation therapy and to see how well it works in treating patients with prostate cancer.

OBJECTIVES:

Primary

• To escalate the dose of stereotactic body radiotherapy (SBRT) to a tumoricidal dose without exceeding the maximum tolerated dose in patients with organ-confined prostate cancer. (Phase I)
• To determine the late, severe grade 3-5 genitourinary and gastrointestinal toxicity occurring between 270-540 days (i.e., 9-18 months) from the start of the protocol treatment as assessed by CTCAE v3.0. (Phase II)

Secondary

• To determine the dose-limiting toxicity of SBRT in these patients. (Phase I)
• To determine the 2-year biochemical (PSA) control (freedom from PSA failure), disease-free and overall survival, local control, freedom from distant metastases, and the incidence of high-grade adverse events of any type in patients treated with this therapy in order to determine if the therapy is promising enough for further clinical investigation. (Phase II)

OUTLINE: This is a multicenter, phase I dose-escalation study followed by a phase II open-label study.

• Phase I: Patients undergo 5 treatments of stereotactic body radiotherapy (SBRT).
• Phase II: Patients undergo SBRT at the maximum tolerated dose as in phase I. After completion of study treatment, patients are followed at 1.5, 3, 6, 9, and 12 months, every 6 months for 5 years, and then once a year for years 5-10.

PROJECTED ACCRUAL: A total of 97 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the prostate

  • Stage T1a, T1b, T1c disease
  • Stage T2a or T2b

• No direct evidence of regional or distant metastases

• No T2c, T3, or T4 tumors

• Gleason score ≤ 7

• Must meet the following criteria:

  • Prostate-specific antigen (PSA) ≤ 20 ng/mL prior to starting hormonal therapy (if given) for patients with a Gleason score of 2-6
  • PSA ≤ 15 ng/mL prior to starting hormonal therapy (if given) for patients with a Gleason score of 7
  • Risk of pelvic lymph node involvement < 20% according to Roach formula

• Ultrasound-based volume estimation of the prostate gland ≤ 60 g

PATIENT CHARACTERISTICS:

• Zubrod performance status 0-2

• Fertile patients must use effective contraception

• No prior invasive malignancy, except for nonmelanoma skin cancer, unless disease-free for a minimum of 3 years (e.g., carcinoma in situ of the breast, oral cavity, or cervix are allowed)

• No significant urinary obstructive symptoms

  • American Urological Association (AUA) score of ≤ 15 (alpha blockers allowed)

• No history of inflammatory colitis (including Crohn disease and ulcerative colitis)

• No history of significant psychiatric illness

• No severe, active comorbidity including any of the following:

  • Unstable angina and/or congestive heart failure requiring hospitalization within the past 6 months

  • Transmural myocardial infarction within the past 6 months

  • Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration

  • Chronic obstructive pulmonary disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy within 30 days prior to registration

  • Hepatic insufficiency resulting in clinical jaundice and/or coagulation defects

    • Laboratory tests for liver function and coagulation parameters are not required for entry into this protocol

  • AIDS (based on current CDC definition) or other immunocompromising condition

    • HIV testing is not required for entry into this protocol

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• More than 9 months since prior hormonal therapy as neoadjuvant therapy or to downsize the prostate gland
• No prior pelvic radiotherapy
• No prior chemotherapy or surgery for prostate cancer
• No prior transurethral resection of the prostate (TURP) or cryotherapy to the prostate
• No plans for other concurrent post-treatment, adjuvant, antineoplastic therapy including surgery, cryotherapy, conventionally fractionated radiotherapy, hormonal therapy, or chemotherapy as part of the treatment for prostate cancer