People make use of the different effects and damages of radiation on the normal and tumor cell populations of various tissues and organs, as well as the differences in their ability to recover, so that radiation therapy becomes one of the main means of treating tumors. Because after the normal tissues are damaged by rays, the automatic stability control system starts to work, the cell proliferation cycle is shortened, and the growth ratio of cells is increased, so that the repair of damaged normal tissues is completed soon. On the other hand, the tumor cell population has its own, different reaction system from the normal tissue after being struck by rays, and the reaction is extremely different among different tumors. During the observation of human tumor cells, it is found that there is an obvious relationship between cell proliferation rate and cell loss and radiosensitivity. Where the average growth rate is the fastest, the growth rate and cell renewal rate are high, the tumors are more sensitive to radiation: general embryonic tumors are the most sensitive to radiation; lymphoid tumors are the second; epithelial tumors are again; and mesenchymal tumors are the most insensitive and need higher doses to play a role. It requires higher doses to be effective. Since normal tissues have automatic stability control system and tumor tissues are different, the recovery and growth of normal tissues and tumor tissues are different after irradiation: ① After irradiation, the cell proliferation cycle of normal tissues will return to normal quickly, while tumor tissues are slow in repairing the damage caused by radiation, and the cell proliferation cycle is prolonged; ② After irradiation, although the tumor may have a temporary accelerated growth phenomenon, the growth rate is still not as fast as the normal tissues to repair the damaged tissues. Although the tumor may have a temporary accelerated growth phenomenon after irradiation, the growth rate is not as fast as the proliferation of normal tissues to repair the damage; ③ The growth rate of tumor cells is larger than that of normal tissues, and there are more cells in the cell cycle, therefore, the ones damaged by lethal injuries are more than that of normal tissues, and the ones damaged by different degrees of injuries are also more than that of normal tissues. Therefore, in the clinical radiotherapy of tumor, the different radiotherapy effects of normal tissue and tumor tissue are used to carry out fractionated radiotherapy, so as to achieve the purpose of killing tumor cells and protecting normal tissue as much as possible. In the clinical treatment of tumors, more than 70% of tumor patients have received radiotherapy, including radical radiotherapy and palliative radiotherapy.