Radiation Therapy Plus Irinotecan in Treating Patients With Colon Cancer

RATIONALE: Radiation therapy uses high energy x-rays to damage tumor cells. Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining radiation therapy with chemotherapy may kill more tumor cells. PURPOSE: Phase I/II trial to study the effectiveness of radiation therapy plus irinotecan in treating patients with colon cancer that is recurrent or that cannot be removed surgically.