Not all patients and families understand radiation therapy, and many confuse radiation therapy with chemotherapy, while others simply do not know what radiation therapy is. Many patients lose a treatment opportunity because of this. I. What is radiotherapy? Radiation therapy for tumors (radiotherapy for short) is the treatment of cancer with radiation, using radiation to kill cells and thus achieve the purpose of treatment. Radiation therapy has been developed for more than a century. After Roentgen’s discovery of X-rays and Madame Curie’s discovery of radium, they were soon used for clinical treatment of malignant tumors, and radiation therapy is still an important local treatment for malignant tumors. About 70% of patients with malignant tumors require radiation therapy at some point in their disease course. The role and status of radiation therapy in tumor treatment is becoming increasingly prominent. Radiation therapy has become one of the main means of treating malignant tumors. Why radiation therapy is still needed after tumor removal? After surgery, many cancer patients think that the cancer is removed, there is no more problem and the treatment is over. The growth of tumor is not only local infiltration, but also can metastasize through lymphatic tract or through blood circulation. Surgery can remove the tumor visible to the naked eye, but for the tumor cells that infiltrate into the normal tissues around the tumor, it is not easy to distinguish them with the naked eye because of the small number, and sometimes the tumor metastasizes to its surrounding lymph nodes, which is also not easy to detect because of the small number of tumor cells. Therefore, many tumors require postoperative radiotherapy. For example, lung cancer, breast cancer, rectal cancer, gastric cancer, some brain tumors, head and neck tumors, soft tissue tumors and so on. Postoperative radiotherapy can significantly reduce the recurrence rate and improve the long-term control rate of tumors. In principle, all patients with breast cancer surgery should be treated with radiotherapy to improve the efficacy. Radiotherapy is also required for patients with risk factors for modified radical breast cancer surgery. Which tumors should be treated with radiotherapy? According to relevant statistics, 40% of tumors can be cured by radiotherapy. The efficacy of radiotherapy for head and neck tumors, nasopharyngeal cancer, early laryngeal cancer, oropharyngeal cancer and hypopharyngeal cancer is certain, and radiotherapy can not only cure tumors but also protect organ function and facial appearance. For chest tumors, such as early-stage lung cancer, radiotherapy has the same therapeutic effect as surgery, while radiotherapy should be preferred for locally advanced lung cancer that loses the chance of surgery; for cervical and upper thoracic esophageal cancer, radiotherapy is often preferred to reduce damage and preserve function. Locally advanced esophageal cancer with lymph node metastasis that cannot be operated should also be treated with radiotherapy. Malignant lymphomas such as nasal NK/T-cell lymphoma, early mycosis fungoides, and inert lymphoma are treated with radiotherapy as a radical treatment. Abdominopelvic tumors such as rectal cancer, cervical cancer, and early-stage seminomatous cell tumors of prostate cancer are all treated with radiotherapy as their primary treatment. In addition, soft tissue tumors and glioma need radiotherapy regardless of whether they are completely removed by surgery or not. For brain metastasis, bone metastasis, superior vena cava syndrome and spinal cord compression radiotherapy can rapidly relieve the symptoms and relieve the pain, so radiotherapy should be preferred.