How long it takes for radiotherapy to take effect mainly depends on the nature, location and size of the tumor, and most of the patients will take effect in 2 weeks to 1 month after radiotherapy. The effect time of radiotherapy cannot be generalized, it depends on the sensitivity of the tumor to radiation, if it is a lymphoma, the tumor may shrink in one week after radiotherapy, and small cell lung cancer may shrink in 2 weeks to 3 weeks. However, in general, the efficacy of radiotherapy is evaluated one month after the end of radiotherapy, at this time, the tissue damage and edema produced by radiotherapy have subsided, and the evaluation of the efficacy is more accurate. About one month after the end of radiotherapy, the best treatment result can be obtained. Radiotherapy patients should have sufficient rest, eat a balanced diet, avoid wearing tight clothes, and consult a doctor if they feel unwell.