The so-called radiotherapy, short for radiation therapy, is a means of treating malignant tumors by using ionizing radiation such as X-rays, γ-rays or electron beams. At present, 60% to 70% of patients with malignant tumors need to receive radiation therapy. The principle of radiation therapy is that radiation can induce certain chemical reactions in cells, tissues and organs, causing changes in the structure of biomolecules, thus destroying and preventing cell division. Due to the high metabolism, tumor cells in the stage of division and reproduction have higher sensitivity to radiation, so radiation can kill tumor cells without causing serious damage to normal tissues. At present, there are three main types of radiation used in radiotherapy: ① a, b, g rays produced by radioisotopes; ② X-ray therapy machines and various types of gas pedals produce X-rays of different energies; ③ various types of gas pedals produce electron beams, proton beams, neutron beams, negative p meson beams, etc. The unit of radiation dose is measured in gorillas, which are used as the unit of radiation dose. The unit of radiation dose is expressed in Gray (Gy). At present, the international unification of 2 grams of material to absorb 100 ergs of ray energy corresponding to the absorbed dose is called 1cGy, that is, in the past said 2 rads (rad), which the relationship between: 1Gy = 100cGy = 100 rad. This refers to the unit of energy absorbed by the tissues or tumors, that is, the tumor tissues are subjected to the amount of radiation. Two commonly used irradiation methods are extracorporeal irradiation and intracorporeal irradiation. In vitro irradiation is the irradiation of radiation at a certain distance from the patient, focusing on irradiating a certain part of the body, which can be divided into proximity (15-40 cm) and distance (60-150 cm) irradiation according to the difference in the distance of the irradiation. The volume of irradiated tissues and its relationship with neighboring tissues must be accurately calculated by radiation projection technology, and electronic computers and simulators are used to select and adjust the appropriate irradiation field to ensure that the tumor is accurately located in the radiation field. Tumors located in the deep part of the body require the use of multi-field irradiation or rotational irradiation in order to achieve the exact therapeutic effect. In vivo irradiation is to insert the radioactive object directly into the tumor (e.g. skin cancer, tongue cancer, breast cancer, etc.) or organs (e.g. esophagus, uterine cervix, rectal cancer, etc.) for irradiation, which is known as intertissue placement irradiation and intracavitary irradiation, respectively. In recent years, the technology of post-installation of radioactive source is mostly adopted, which means that the source container or catheter without radioactive source is firstly placed into the human body cavity or inserted into the tissues, and then under the condition of protection and shielding, the radioactive source is inputted into the source container for radiotherapy by using the automatic control. Clinically, before radiation therapy is performed, the doctor has to formulate the amount of radiation therapy according to the site, type, size, staging and other clinical information of the tumor. These radiation doses, however, need to be divided into several irradiations to complete. After years of research, it has been found that for most cancers, 2 Gray (Gy) per irradiation, 5 times per week (i.e., conventional irradiation dose) works better (dose splitting). Patients are accustomed to speaking of each irradiation as baking 2 electrics. For different tumors with different therapeutic goals, the dose of 2 electrics is different. Patients undergoing radiotherapy should first have confidence in the treatment of their disease and should work hard with their doctors to ensure that their treatment plan is completed successfully and on schedule. During radiotherapy, patients may experience varying degrees of systemic and localized reactions due to the effects of radiobiology. These reactions can gradually subside after the end of radiotherapy, and patients should be prepared for them and should not be afraid of them, let alone mistaking them for treatment failure or deterioration of the disease. During the radiotherapy period, patients should arrange their life reasonably, ensure sufficient sleep and rest, do not do strenuous exercise or physical labor, eat more fresh food rich in vitamins and high protein, and avoid stimulating food. Smoking and alcohol should also be avoided. The position and posture when receiving radiotherapy should be strictly in accordance with the doctor’s instructions. The skin of the irradiated area of the patient should be kept clean and hygienic, and should not be washed with water or scratched by hand to avoid mosquito bites. Irritating drugs or drugs containing metal ions should not be used in the irradiated area, and adhesive tape should not be applied. Patients receiving radiation therapy in outpatient clinics should contact the doctor in charge every week to let the doctor know their reaction and discomfort to radiation therapy and make blood routine and other tests in time.