Selenium in Treating Patients Who Are Undergoing Brachytherapy for Stage I or Stage II Prostate Cancer

RATIONALE: The use of nutritional supplements, such as selenium, may stop prostate cancer from growing. Internal radiation, such as brachytherapy, uses radioactive material placed directly into or near a tumor to kill tumor cells. Giving selenium before brachytherapy may be an effective treatment for prostate cancer. PURPOSE: This randomized phase I trial is studying selenium to see how well it works compared to placebo in treating patients who are undergoing brachytherapy for stage I or stage II prostate cancer.