Weakness after radiotherapy may be caused by decreased immunity, and patients should pay attention to related matters according to the doctor’s instructions. Radiotherapy refers to the local treatment by radiation, which is mainly used to eliminate and eradicate the primary foci and metastatic foci of local tumors. However, because radiotherapy is to irradiate the tumor through penetrating rays to make the lesion shrink, thus playing a therapeutic effect. When the radiation penetrates the human body, it will cause harm to the normal tissues of the human body, and if the irradiation range is too large, it may also induce serious complications. At the same time, patients may also experience skin damage, nausea, vomiting, fever, bone marrow suppression and other side effects after radiotherapy, all of which may lead to a decrease in the patient’s immunity, which may result in symptoms of fatigue. After the completion of radiotherapy, patients need to pay attention to rest, and also need to under the guidance of the doctor for regular review, avoid overwork. It is recommended that patients strictly follow the doctor’s instructions for radiotherapy, and also need to do a good job of their own care under the guidance of the doctor, so as to avoid adverse effects on the body.