Radiation therapy, commonly known as “light” and “baking” in the north, is the use of radiation to kill tumors for the purpose of treating tumors, and is one of the main treatments for malignant tumors. It has a history of more than 100 years, from the initial discovery of radium by Madame Curie to deep x-ray therapy, and in the 1950s to 60 cobalt therapy machines and later gas pedal therapy. Radiation is invisible to the naked eye and can be produced by the decay of radionuclides or by x-ray machines or various types of gas pedals. Radiation therapy is widely used in the treatment of tumors, and 60% to 70% of tumor patients have to apply radiation therapy in the treatment process. According to the purpose of treatment, it can be divided into radical treatment and palliative treatment. With the update of treatment equipment and improvement of technology, the efficacy of radiation therapy has been greatly improved. Certain tumors such as head and neck tumors including nasopharyngeal cancer, tonsil cancer, laryngeal cancer and Hodgkin’s disease have better efficacy, while some patients with advanced tumors can also undergo palliative radiation therapy to achieve pain relief, hemostasis and anti-inflammatory effects, so as to reduce patients’ pain and improve their survival quality. Radiation therapy can not only cure tumors, but also protect normal tissue functions, such as facial skin cancer, tongue cancer, larynx cancer, etc. After treatment, it can preserve appearance and maintain functions such as eating and vocalization. This is not easily achieved by other therapies. The conventional radiation therapy method is once a day, five times a week, with a dose of 1.8-2Gy each time, and the total dose is 60-70Gy, and the total course of treatment is 6-7 weeks. Nowadays, different radiation therapy segmentation methods such as hyper-segmentation radiation, accelerated hyper-segmentation, etc. are also carried out and are currently under clinical trial. Radiation therapy is carried out in two basic ways: one is external long-distance irradiation, commonly known as external irradiation, which is used for most tumors; the other is brachytherapy, including intracavitary, intertissue and postoperative irradiation with intraoperative placement. The choice is determined by the doctor according to the condition.