Radiation therapy is one of the three most important means of treating malignant tumors and has a history of 100 years. Local control of the primary tumor is a prerequisite for tumor cure. Surgery and radiotherapy are both treatments for local removal of tumors, while radiation therapy uses rays to kill tumor cells. Approximately 70% of patients with malignant tumors require radiation therapy. According to the biological behavior of tumors, some tumors can be treated with radiation therapy mainly for the purpose of radical treatment. Radiation therapy is an important option for local control of tumors in patients who are not suitable for surgery or have lost the opportunity for surgery and have residual or suspected tumor residues after surgery. In order to achieve the goal of increasing the radiation dose to the tumor target area, improving the local control rate, reducing the dose to the normal tissues around the tumor, preserving the normal function of important organs and improving the patient’s survival quality to achieve the modern tumor cure. In recent years, with the continuous development and update of computer technology, medical imaging technology and image processing technology, radiation therapy equipment has been developed and updated with new technology of radiation therapy, such as stereotactic radiotherapy, 3D conformal radiotherapy and intensity modulated radiotherapy, which have been introduced and improved and developed successively, so that tumor radiotherapy has entered a new era. Conventional and three-dimensional conformal radiotherapy (3DCRT): (1) Radical radiotherapy: when the tumor is limited or only adjacent tissue invasion or lymph node metastasis and the tumor is more sensitive to radiation, radiotherapy can be used as a radical treatment, such as nasopharyngeal cancer and other head and neck tumors, lung cancer, esophageal cancer, lymphatic system malignant tumors, prostate cancer, cervical cancer, etc. Prostate cancer, cervical cancer, etc. Early stage breast cancer can be treated by local surgical excision with radical intensity-modulated radiotherapy, which can preserve the appearance and function of breast and obtain the same efficacy as radical surgery, and this technology is widely carried out at home and abroad. radiotherapy can improve the resection rate of tumor, reduce the chance of tumor implantation during surgery and the recurrence rate after surgery, which is applicable to esophageal cancer, laryngeal cancer, maxillary sinus cancer, soft tissue sarcoma, rectal cancer, etc. (4) Postoperative radiotherapy: for tumor with residual, lymph node metastasis or subclinical lesions after resection, postoperative radiotherapy can improve the local control rate of tumor, which is commonly used for brain tumor, esophageal cancer, lung cancer, breast cancer, kidney cancer, soft tissue sarcoma, etc. It is commonly used for brain tumor, esophageal cancer, lung cancer, breast cancer, kidney cancer, soft tissue sarcoma, etc. (5). Intraoperative radiotherapy: It is a high-dose radiotherapy that is administered directly to the resected tumor bed during surgery to reduce the postoperative recurrence rate and to give high-dose kill to the areas that may not be completely resected, commonly used in the treatment of gastric cancer, pancreatic cancer, rectal cancer and brain tumor. IMRT is the most advanced radiotherapy technology in the world based on advanced radiotherapy planning system and accelerator equipment, which means that by changing the radiation intensity in the target area, the ideal uniform dose distribution can be obtained at any point in the target area, and at the same time, the dose to the vital organs can be limited to the tolerable range according to the doctor’s requirement, so that the dose to the normal tissues immediately outside the target area can be minimized, which can effectively improve the local control rate of tumor, reduce the complications of normal tissues, and improve the quality of life of patients after treatment. The calculation of dose is achieved through the 3D treatment planning system with inverse calculation function to achieve the precise positioning of the target area, and the premise of achieving IMRT is achieved through CT with 3D image processing, analog positioning machine This high-precision radiotherapy technology makes tumor radiation therapy cross into a new era. Main indications of radiation therapy: (1) Head and neck tumors: nasopharyngeal cancer, laryngeal cancer, thyroid cancer, tongue cancer, oral cancer, etc. (2) Thoracic tumors: breast cancer, esophageal cancer, lung cancer, mediastinal tumors, etc. (3) Lymphatic system tumors: malignant lymphoma, etc. (4) Gastrointestinal system tumors: liver cancer, pancreatic cancer, rectal cancer, anal cancer, etc. (5) Tumors of urinary system: kidney cancer, adrenal tumor, bladder cancer, prostate cancer, testicular tumor, etc. (6) Female reproductive system tumors: cervical cancer, endometrial cancer, vulvar cancer, vaginal cancer, ovarian cancer, etc. (7) Bone tumors: osteosarcoma, myeloma, fibrosarcoma, Ewing’s tumor, giant cell tumor and bone metastases, etc. (8) Neurological tumors: malignant glioma, pineal tumor, medulloblastoma, pituitary tumor, meningioma, craniopharyngioma, ventricular meningioma, intraspinal tumor and brain metastases. (9) Skin cancer malignant melanoma, basal cell carcinoma. (10) Soft tissue tumors. (11) Malignant sarcoidosis. (12) Ophthalmic and intraorbital tumors.