Radiation therapy, or radiotherapy for short, is commonly known as “electrotherapy”. It is one of the three major treatment methods (surgery, radiotherapy and chemotherapy) for tumors. According to statistics, 65-75% of malignant tumor patients need to receive different forms of radiotherapy at some stage of their treatment, while some early cancer patients such as nasopharyngeal cancer, laryngeal cancer and Hodgkin’s disease can be cured by simply receiving radiotherapy. According to WHO statistics at the end of 1998, 45% of tumor patients can be cured, of which 22% rely on surgery, 18% on radiotherapy and 5% on chemotherapy, and the most obvious advantage of radiotherapy over surgery is that it can be preserved. The application of three-dimensional conformal radiotherapy technology has the following advantages: 1. It can reduce the unnecessary irradiation damage caused by too large an irradiation range in traditional radiotherapy and the treatment failure caused by too small an irradiation range; it can increase the target dose under the premise of protecting normal tissues and organs, so as to kill tumor cells more effectively, improve the function of tumor patients’ organs and meet patients’ cosmetic desires. In recent years, with the continuous development of radiotherapy technology, the significant contribution of radiotherapy in tumor treatment is becoming more and more prominent. In particular, the new precision radiotherapy technologies developed at the turn of the century – 3D conformal radiotherapy and intensity-modulated radiotherapy – can greatly reduce radiation toxicity and side effects while improving tumor cure rate, thus creating a new era of tumor treatment. The main feature of 3D conformal radiotherapy is the conformality of the field shape, i.e. the angle and field shape of each irradiation in the three-dimensional space are consistent with the projection of the outer contour of the target area. The survival rate of patients and improvement of their quality of life compared with conventional radiotherapy have been confirmed in the clinical practice of conformal radiotherapy for nasopharyngeal cancer, lung cancer, prostate cancer and intracranial tumors. 2.Precise body fixation devices (such as thermoplastic body film and vacuum bag, etc.), three-dimensional positioning technologies (such as CT, MRI, SPECT positioning plus 3D reconstruction, etc.) and treatment body verification devices (such as electron beam imaging, EPID, CBCT, etc.) are adopted, which greatly improve the positioning accuracy, positional accuracy and irradiation accuracy of radiotherapy. In the design stage of 3D conformal radiotherapy, by outlining the tumor target area and surrounding normal tissues and organs, a computerized treatment planning system (TPS) can be used to calculate and evaluate the dose distribution of the target area and the actual irradiation dose of the surrounding normal tissues and organs, which is helpful for clinicians to verify the feasibility of the treatment plan more accurately and select a better treatment plan. IMRT not only has the advantages of 3D conformal radiotherapy, but also can achieve conformal dose distribution, i.e., by optimizing the weighting of each beam in the field, the distribution of high dose area in 3D direction is consistent with the actual shape of the target area, while the normal tissues and organs adjacent to the target area are less irradiated due to The normal tissues and organs adjacent to the target area are less damaged by the sharply reduced dose. Theoretically, all patients with indications for radiotherapy can be treated with 3D conformal radiotherapy or intensity-modulated radiotherapy, which can be used for most primary brain tumors and metastases, head and neck tumors (nasopharyngeal cancer, tongue cancer, oral cancer, laryngeal cancer, etc.), chest tumors (lung cancer, esophageal cancer, mediastinal tumors, breast cancer), abdominal tumors (liver cancer, pancreatic cancer, abdominal metastases), urinary tumors (kidney cancer, prostate cancer, bladder cancer), gynecological tumors (cervical cancer), and other tumors. It also has good effect on benign tumors such as pituitary tumor, craniopharyngioma, cerebral arteriovenous malformation, vertebral hemangioma and hepatic cavernous hemangioma. Intensity-modulated radiotherapy is also particularly suitable for tumors with complex anatomical structures, such as nasopharyngeal cancer, maxillary sinus cancer and intracranial tumors; or tumors with irregular shapes and important surrounding organs or tissue structures, such as lung cancer, esophageal cancer and prostate cancer; or tumors with multiple targets. As one of the precise radiotherapy techniques, 3D conformal radiotherapy and intensity-modulated radiotherapy can maximize the radiation dose to the target area to kill tumor cells through precise positioning, precise planning and precise treatment, while leaving the surrounding normal tissues and organs with less or no irradiation damage, therefore, many experts and scholars at home and abroad call it a revolution in the history of radiotherapy. Therefore, many experts and scholars at home and abroad call it a revolution in the history of radiotherapy. It can not only achieve a high cure rate of tumor, but also preserve the function of patients and improve the quality of survival, which is the mainstream of tumor radiotherapy in the 21st century.