In recent years, the incidence of tumors has been increasing year by year. Currently, the main treatments for tumors are still surgery, radiotherapy and chemotherapy. Radiotherapy, like surgery, is a local treatment method. With the development of radiation physics, computer technology and medical imaging technology, radiation therapy for tumors has developed rapidly, and many advanced radiotherapy techniques have been gradually applied in clinical practice, such as three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated conformal radiotherapy (IMRT), image-guided radiotherapy (IGRT) and tomotherapy. The clinical application of these cutting-edge technologies has led to a qualitative change in the radiotherapy mode – that is, from the two-dimensional irradiation mode in the past to the precise radiotherapy mode with three-dimensional positioning. Therefore, it is said that the 21st century is the century of precision radiotherapy for tumors! It is because of this transformation of radiotherapy mode that the status of radiotherapy technology in tumor treatment is getting higher and higher. According to WHO statistics, the 5-year survival rate of systemic malignant tumors has reached 45% (an average increase of 15% every 30 years), of which the contribution of surgery is 22%, radiotherapy is 18%, and chemotherapy and other treatments are 5%. With the vast majority of patients treated with radiotherapy being advanced patients, the contribution rate is still 18%, and its importance to tumors is evident! In foreign countries, about 65%-75% of patients with malignant tumors have experienced radiation therapy.