Radiation therapy is a method that uses the selective radiation of X-rays or other ionizing radiation and the radioactivity of radioactive elements to destroy cells and tissues to achieve the purpose of treatment. The disadvantage is that while radiation destroys and kills tumor cells, it also has a destructive effect on the surrounding normal tissue cells. At present, the more perfect and practical radiotherapy techniques are: conventional irradiation technique, X-knife technique, 3D conformal irradiation technique, 3D intensity modulation irradiation technique. There are two main types of irradiation: in vitro and in vivo. Intracorporeal irradiation is the direct insertion of radiation source into the tumor (e.g. skin cancer, tongue cancer, etc.) or the internal cavity of the organ (e.g. esophagus, cervix) for irradiation, which are called intertissue irradiation and intracavity irradiation respectively, and nowadays, most of the radiation sources are rear-mounted for intracorporeal irradiation. In vitro irradiation is a certain distance from the person and concentrates on irradiating a certain area. According to the shooting distance, there are two kinds of irradiation: near distance (15-40 cm) irradiation and far distance (60-150 cm) irradiation. The difference between them is that: the intensity of the radiation source of in vivo irradiation is smaller, so the treatment distance is shorter, and most of the energy is absorbed; most of the ray energy of in vitro irradiation is screened out, and only a small part of the energy reaches the tissue. In vitro radiation reaches the tumor through the skin and normal tissues. With the tolerance and sensitivity of different tumors, different types of radiation with different energies and multifield irradiation techniques should be selected.