When receiving radiotherapy, almost all patients receiving radiotherapy are accompanied with side effects of different degrees. The severity depends on the irradiation site, the size of the irradiation field, each split dose, total dose and radiotherapy energy. Before radiotherapy or combined with chemotherapy at the same time, especially when chemotherapeutic drugs with radiosensitizing effect, such as adriamycin and daunorubicin, increase the sensitivity of radiotherapy and increase the side effects. In addition, It is also related to the cell proliferation and renewal of organs and tissues. Cells with strong proliferation and low differentiation are more sensitive to rays, such as gastrointestinal mucosa, oral mucosa and bone marrow, while other tissues and organs such as nerves, muscles, liver and kidney are not sensitive, and the damage caused by rays is much lighter than that of sensitive tissues.