Cancer of the colon and rectum is very common in the U.S. Early tumors can be cured with surgical removal, however larger tumors or cancers in the lower rectum frequently require 5 or 6 weeks of radiation, given before or after surgery (with or without chemotherapy depending upon other factors), to prevent recurrence and/or a permanent colostomy. Tomotherapy permits reduction of dosage to the small intestines while permitting successful treatment of the colon or rectum and its draining lymph nodes. This may reduce the likelihood of long term bowel problems as well as the possibility of post-surgical complications.

Colorectal cancer can also spread to the liver; frequently it is the only site of spread. Since the liver is very sensitive to radiation, in the past it has been difficult to treat liver metastases with radiation without damaging the liver. Tomotherapy now allows us to accurately target liver tumors to receive fairly high doses of radiation, while safely sparing the rest of the liver.