Capecitabine, Panitumumab, and Radiation Therapy With or Without Irinotecan Hydrochloride in Treating Patients Undergoing Surgery for Localized Rectal Cancer

RATIONALE: Drugs used in chemotherapy, such as capecitabine and irinotecan hydrochloride, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Monoclonal antibodies, such as panitumumab, can block tumor growth in different ways. Some block the ability of tumor cells to grow and spread. Others find tumor cells and help kill them or carry tumor-killing substances to them. Radiation therapy uses high-energy x-rays to kill tumor cells. Giving chemotherapy, monoclonal antibody therapy, and radiation therapy before surgery may make the tumor smaller and reduce the amount of normal tissue that needs to be removed. PURPOSE: This phase II trial is studying the side effects of giving capecitabine and panitumumab together with radiation therapy with or without irinotecan hydrochloride and to see how well it works in treating patients undergoing surgery for localized rectal cancer.