In external beam radiation therapy, physicians target cancer cells with radiation beams. In local radiation therapy, or brachytherapy, physicians place a small pellet of radioactive material directly into the cancer. Radiation therapy is often used along with surgery. Before surgery, radiation may be used to shrink the tumor. After surgery, radiation can kill leftover deposits of cancer not seen during the surgery.
Radiation can also ease symptoms of advanced cancer, such as intestinal blockage, bleeding, or pain.
The side effects of radiation therapy include mild skin irritation, nausea, diarrhea, or fatigue. Physicians use chemotherapy to treat cancer that has spread beyond the colon or to relieve the symptoms of advanced cancer. Sometimes, 5-FU is more effective when given with other drugs, such as leucovorin or levamisole. For patients who do not respond to fluorouracil therapy, physicians may prescribe a drug called Irinotecan. Chemotherapy drugs kill cancer cells, as well as normal ones.