Generally, only one course of radiation therapy is given to the same site, but if local recurrence occurs, a second course of radiation therapy may be given after comprehensive consideration, but the interval between the two courses of radiation therapy is a very careful choice between the therapeutic benefit of the two courses of radiation therapy for the patient and the tolerability of the two courses of radiation therapy. If the interval is more than 1 year, the second course of radiotherapy may be relatively safe. In addition, after chest radiotherapy for small cell lung cancer, often combined with chemotherapy in the mode of prophylactic brain irradiation due to a high risk of brain metastatic cancer, such as the tumor with bone metastasis, as well as metastatic sites are different, often the patient can receive several multiple courses of radiation therapy. However, for the same localized site, usually only one radiation therapy is chosen, and if the local control rate is relatively good, there is no need for a second radiation therapy.