Indications for radiation therapy for rectal cancer. The main purpose of radiotherapy or radiotherapy for rectal cancer is adjuvant and palliative treatment. The indications for adjuvant treatment are mainly for ~-stage rectal cancer; the indications for palliative treatment are local recurrence of tumor and/or distant metastasis. For some patients who cannot tolerate surgery or have a strong desire to preserve anus, radical radiotherapy or radiochemotherapy can be tried. Radiotherapy is not recommended for stage i rectal cancer. However, radical surgery is recommended after local resection with one of the following factors; if refusal or inoperability to operate, postoperative radiotherapy is recommended. (1) postoperative pathological stage of t2; (2) tumor maximum diameter greater than 4 cm; (3) tumor occupying more than 1/3 of the bowel circumference; (4) low-differentiated adenocarcinoma; (5) nerve invasion or vascular tumor embolus; (6) positive incision margin or tumor distance from the incision margin