DISEASE CHARACTERISTICS: Histologically confirmed pelvic cancer Planned therapy is to undergo continuous definitive or adjuvant external beam pelvic radiation therapy with or without fluorouracil (5-FU) plus or minus levamisole No split course radiation therapy Planned course of radiation therapy must also meet the following criteria: - Entire pelvis must be encompassed by the planned radiotherapy fields - Total planned dose to the central axis midplane or isocenter for the whole pelvic field must be between 4500-5350 cGy - Treatment must be given 4-5 times per week on a one-treatment-per-day basis No stool incontinence or stool frequency of 7 or more per day prior to initiation of radiation therapy Must be entered on study before the second radiation therapy fraction No current or prior metastases beyond pelvic regional lymph nodes Must have functioning rectum No planned perineal irradiation No anal cancer No active intraluminal gastrointestinal (GI) tumors Patients with completely resectioned GI tumors who also receive adjuvant treatment are eligible