RATIONALE: Radiation therapy uses high-energy x-rays to damage tumor cells. Multiple CT scans may improve the accuracy of radiation therapy for prostate cancer.

PURPOSE: Phase I trial to study the effectiveness of multiple CT scans in guiding the treatment of patients who have prostate cancer and are undergoing radiation therapy.

OBJECTIVES:

• Compare the accuracy of radiotherapy delivery using multiple CT scans to guide patient positioning vs the standard portal image guided procedure in patients with prostate cancer undergoing external beam radiotherapy.
• Determine the reduction in the proportion of patients with large target positioning errors using the CT-guided procedure.
• Determine organ motion and setup errors over the course of radiotherapy in order to develop efficient clinical intervention strategies in these patients.

OUTLINE: Patients undergo radiotherapy over 9 weeks. Patients undergo a CT scan immediately prior to receiving radiotherapy on treatment days 3-8 and then weekly thereafter. On 3 different days, patients also undergo CT scan immediately after radiotherapy. If the CT scans indicate a correction that exceeds the action level currently in effect, then beginning with the next treatment, the patient's position with respect to the radiation field is adjusted.

PROJECTED ACCRUAL: A total of 25 patients will be accrued for this study within 2 years.

DISEASE CHARACTERISTICS:

• Undergoing external beam intensity-modulated radiotherapy for prostate cancer
• Able to maintain treatment position for about 40 minutes

PATIENT CHARACTERISTICS:

Age:

• Not specified

Performance status:

• Not specified

Life expectancy:

• Not specified

Hematopoietic:

• Not specified

Hepatic:

• Not specified

Renal:

• Not specified

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• Not specified

Endocrine therapy:

• Not specified

Radiotherapy:

• See Disease Characteristics

Surgery:

• Not specified