Radiation therapy (commonly known as electrotherapy) is one of the three major means of treating malignant tumors at present. According to statistics, about 2/3 of all tumor patients need to use or cooperate with radiation therapy. The principle of radiotherapy for tumor treatment is to kill cancer cells by using radiation. Since tumor cells grow in normal tissues or are very close to important normal tissues or organs, and their shapes are irregular, two situations will arise: 1. In order not to miss them, the scope of radiation therapy must be large enough to include tumor cells in the irradiation field, the consequence of which is that more normal tissues and organs around the tumor are unnecessarily irradiated, increasing the side effects of radiation therapy and This increases the side effects of radiotherapy and radiation damage to normal organs, and reduces the quality of life of patients; 2. In order to avoid injuring important organs, the dose is compromised, and as a result, the tumor cannot be completely killed, laying hidden dangers for metastasis and recurrence. As a means of local treatment, the ideal radiotherapy is to kill tumor cells to the maximum extent while protecting the surrounding normal tissues and organs to the maximum extent, like a modern precision-guided missile, which points to and hits there without hurting the innocent. Three-dimensional conformal intensity-modulated radiotherapy (referred to as intensity-modulated radiotherapy) is such a technology, which represents one of the most important technological advances in modern radiotherapy. Since the 1990s, with the development and application of large high-speed computers in the development of radiotherapy treatment plans and the emergence of digitalized medical linear gas pedals and computer-controlled precision dynamic multileaf collimators, a new radiotherapy technology that enables the distribution of radiotherapy high doses in a three-dimensional direction exactly in line with the shape of the tumor target area has been carried out at home and abroad, enabling intensity control of the subrays within each beam. When it is combined with various image guidance techniques that can precisely outline the target area, the maximum control of dose distribution can be achieved, resulting in higher tumor control rate and lower damage to normal tissues and organs. Therefore, intensity-modulated radiotherapy is called a revolution in the history of radiation oncology and is the mainstream or direction of modern radiotherapy technology. The operation steps of intensity-modulated radiotherapy: 1. Position fixation technology: special individualized fixators are used to ensure that the position of patients can be consistent and impartial for each treatment; 2. will cause serious damage, or which organs will significantly affect the quality of life of patients after irradiation, outline these tissues or organs and then give certain dose restriction conditions to protect them; 4. Design and evaluation of treatment plan: design a treatment plan suitable for each patient according to the purpose of tumor treatment and the requirements of dangerous organs protection and evaluate the control rate of tumor and the probability of damage to dangerous organs; 5, Validation and implementation of treatment plan: The treatment plan that is evaluated satisfactorily is verified by dose on the treatment machine in advance to ensure that the actual treatment can meet the design requirements before officially starting the treatment. Intensity-modulated radiotherapy is applicable to nasopharyngeal cancer, prostate cancer, rectal cancer, breast cancer, pancreatic cancer, liver cancer, central nervous system and other systemic tumors. The application of intensity-modulated radiotherapy can further increase the tumor dose and decrease the normal tissue dose, improve the efficacy and reduce complications. For example, the local control rate of nasopharyngeal cancer treated with intensity-modulated radiotherapy can reach about 95%, and the parotid gland is protected to avoid dry mouth; the dose of prostate cancer treated with intensity-modulated radiotherapy can be increased from 68Gy to 81Gy, the 3-year control rate can be increased from 48% to 94%, and the rectal reaction can be reduced from 57% to 2%; the occurrence of radiation pneumonia can be avoided with intensity-modulated conformal treatment for breast cancer. Intensity-modulated radiotherapy is one of the most active research fields in the oncology field, and major oncology hospitals or oncology centers at home and abroad have carried out intensity-modulated radiotherapy one after another and achieved encouraging clinical efficacy, and intensity-modulated conformal radiotherapy will replace the current conventional radiotherapy technology and become a new conventional technology.