About one month after radiotherapy, try not to do colonoscopy, because the body is weaker after radiotherapy, and generally need to wait for the body to recover before doing colonoscopy. Radiotherapy refers to irradiating the primary or metastatic foci of local tumors through radiation to kill or limit the growth and reproduction of cancer cells, so as to achieve the purpose of treating tumors. Because of the use of radioactive substances, radiotherapy is a more damaging treatment with shorter treatment time but longer treatment period, and it takes about 30-50 days to complete the full treatment course. Colonoscopy is a more intuitive and accurate method of examining colon and rectal lesions, which can electronically transmit images to a display device to observe mucosal lesions in the rectum and colon. After radiotherapy, the body’s immunity is reduced, at this time to do colonoscopy may appear intestinal infection and other complications, in the non-essential case is not recommended to do colonoscopy immediately after radiotherapy. Patients after radiotherapy should also eat low-salt, low-fat soft food, more vitamins and high-quality animal protein, to help the recovery of hematopoietic function, improve the liver and kidney function, prohibit the consumption of spicy and stimulating food, and after the end of the recovery period in the doctor’s permission to carry out colonoscopy again.