Radiotherapy is radiation therapy, which can irradiate cancer tumors locally through radiation. Some tumors sensitive to radiotherapy can achieve the effect of eliminating local primary tumors or metastatic lesions through radical radiotherapy, therefore, the statement that patients cannot live long after radiotherapy is not correct, the survival period has nothing to do with radiotherapy itself, and some patients may prolong their survival period through radiotherapy. However, radiotherapy has certain side effects, plus the gradual weakening of cancer patients in the middle and late stages, which may lead to the deterioration of patients’ physical condition. Radiotherapy is divided into external and internal irradiation, which can cause damage to human body. Since cancer cells and normal cells exist at the same time, and radiation needs to pass through normal tissues around the tumor to reach the tumor lesion, therefore, while killing cancer cells, it can also damage normal cells and even cause normal cells to die. At the same time, the cancer tumor grows faster in the middle and late stages of cancer patients and absorbs nutrients from the body, resulting in the patients’ body wasting and malnutrition. After radiation therapy, adverse reactions will gradually increase and symptoms such as nausea, vomiting, fever, pain, hair loss and skin rash may occur. However, as the cancer cells will be inhibited from growing, it is beneficial to the patient’s organism overall. After radiation treatment, the examination shows that the white blood cell and platelet counts will drop and the immunity of the patient’s organism will also be reduced. At this time, pathogenic bacteria are prone to attack the organism, which may lead to aggravation of the disease or even death if care is not taken seriously. However, with the advancement of medical technology, the side effects after radiotherapy gradually decrease, and together with other treatments, the quality of survival of patients can usually be improved and their survival period extended.