In lung cancer radiotherapy, the side effects are as follows: 1. The most common one is radiation pneumonia, acute radiation pneumonia can appear in the course of radiotherapy and within 1-3 months after radiotherapy. In severe cases, high fever and dyspnea can be seen. Chest X-ray or CT can reveal exudative patches of lung consistent with the radiotherapy field. In mild cases, cough can be treated symptomatically, while in severe cases, hormone, anti-inflammatory and oxygen can be given; 2. 3 months after the end of radiotherapy, sometimes there may be advanced radiation lung injury, which may be radioactive pulmonary fibrosis; 3. There may also be bone marrow suppression and white blood cell reduction, because nowadays, for especially locally advanced non-small cell lung cancer or limited-stage small cell lung cancer, radiotherapy and chemotherapy are synchronized, and the bone marrow suppression may be heavier, and the corresponding radiotherapy side effects are heavier than those of radiotherapy alone, so clinical attention must be paid. Under the conditions of today’s precise treatment and modern advanced radiotherapy technology, the protection of normal heart tissue is getting better and better, and very serious radiation damage is actually becoming less and less common.