Radiotherapy is one of the main means of treating malignant tumors, giving an accurate and uniform dose to a certain volume of tumor to kill tumor cells, and is a means of local and regional treatment. The basic goal of radiotherapy is to strive to improve the therapeutic gain ratio of radiotherapy, i.e. to maximize the dose of radioactivity concentrated in the lesion area to kill tumor cells while leaving the surrounding normal tissues and organs with less or no unnecessary irradiation. The ideal radiation therapy technique is to give a high lethal dose to the target area according to the shape of the tumor, while the normal tissues around the target area are not irradiated. Radiation therapy has evolved from conventional irradiation to conformal radiotherapy, to intensity-modulated radiotherapy, and then to four-dimensional radiotherapy. General radiotherapy is the main treatment modality before conformal radiotherapy. It is a two-dimensional radiotherapy, which is simple to locate and low cost, but it is difficult to set the field in line with the shape of the tumor, and the surrounding normal tissues are heavily irradiated and have heavy reactions. However, it is difficult to match the shape of the tumor and the surrounding normal tissues are exposed to large amount of radiation and have heavy reactions. General radiotherapy cannot accurately evaluate the dose of radiation in each area and may result in underdose in the target area, which affects the treatment effect. Three-dimensional conformal radiotherapy (CRT) is to form a ray beam with the same shape as the tumor or irradiation site (target area) by multi-leaf grating in different irradiation directions, and the normal tissues and organs are shielded from unnecessary irradiation, so the damage is small, which is suitable for the treatment of various malignant tumors, and is conducive to improving the radiotherapy dose and can improve the survival in some tumors. However, for tumors such as nasopharyngeal carcinoma, hypopharyngeal carcinoma, breast cancer, and chest radiotherapy that requires simultaneous irradiation of the supraclavicular region, 3D conformal radiotherapy is difficult to achieve the same shape as the target area, and intensity-modulated radiotherapy may be required. IMRT is particularly suitable for tumors with irregularly shaped target areas and important surrounding tissues and organs. Intensity-modulated radiation therapy also allows simultaneous dose addition to the tumor. However, IMRT has a longer treatment time and higher cost than conformal radiotherapy for a single irradiation. Image-guided radiation therapy (IGRT) is a four-dimensional radiation therapy technique, which adds the concept of time factor to the three-dimensional radiation therapy technique and fully takes into account the movement of anatomical tissues during treatment and the displacement errors between fractional treatments, such as respiratory and peristaltic movements, daily positioning errors, contraction of the target area, etc., which cause changes in radiation dose distribution and affect the treatment plan. Before and during the treatment, we use various advanced imaging devices to monitor the tumor and normal organs in real time, and adjust the treatment conditions according to the changes in the position of the organs so that the irradiation field can closely follow the target area, so that the treatment can be truly precise.