Why radiotherapy is necessary after lung cancer surgery: As the growth of tumor mainly manifests itself as infiltrative growth like tree roots, there are often some subclinical lesions that need microscope to be detected outside the large tumor visible to the naked eye, and these lesions are sometimes difficult to be cut by surgery, which becomes the root cause of recurrence, and the surgery can only be performed to remove the tumor seen by the naked eye, but it can’t achieve the purpose of eradicating the sub-cancer nowadays, therefore radiotherapy is indispensable to prevent recurrence of cancer. Therefore, postoperative radiotherapy is essential in order to prevent cancer recurrence. Which lung cancer patients need radiotherapy? Postoperative lung cancer patients are not all suitable for radiotherapy, but according to the pathological diagnosis of patients, radiotherapy treatment should be selected according to the patients’ conditions, at present, there are the following categories of people who need radiotherapy: 1. Small-cell lung cancer. Small cell carcinoma is prone to metastasis, therefore, large irregular field irradiation is mostly used, and the irradiation area should include the primary foci, even the liver and brain, mediastinum bilateral supraclavicular area and other parts of the body, meanwhile, it should be supplemented with drug treatment. 2.Small foci after recurrence of lung cancer. For lung cancer patients who recur again after surgery, if they cannot receive surgery again the best treatment is directed radiotherapy. The best treatment is targeted radiotherapy, which is a large-dose focused irradiation treatment for an isolated single lesion.