The indications of radiotherapy for rectal cancer are as follows: 1. For stage I rectal cancer, if the tumor is close to the anus, local surgery plus postoperative radiotherapy can be used to preserve the anus and improve patients’ quality of life; 2. For stage II rectal cancer, active preoperative synchronous radiotherapy can be used to reduce the risk of postoperative recurrence and improve the survival rate; 3. For stage III rectal cancer, active preoperative synchronous radiotherapy can also be used to reduce the postoperative local recurrence rate and extend the survival rate; 4. For stage IV rectal cancer, palliative radiotherapy can be used to improve patients’ quality of life.