Radiation therapy is a primary treatment for anal and distal rectal lesions when the patient is a poor risk for primary surgery.
Postoperative radiation therapy may be useful for Stage II or III colon cancer that is fixed or adherent to adjacent structures, or had complete obstruction or perforation.
Radiation therapy is more useful for rectal lesions than for colon lesions. Both pre-operative and post-operative irradiation are used to prevent local recurrence from rectal lesions. High-dose preoperative radiation may permit resection of primary tumor with preservation of sphincter function.
Hepatic radiation for known or suspected liver metastases (under clinical evaluation)
Intracavitary radiation may be used in selected rectal cancer patients (well-differentiated tumor < 2 cm in size, no fixation or palpable lymph nodes).
Intraoperative radiation is an option (where available) for locally advanced rectal disease.