Breast-conserving surgery does not necessarily require radiotherapy, and it is necessary to judge whether radiotherapy is needed according to the severity and risk of the disease. 1. No radiotherapy is needed: if the patient belongs to early in situ breast cancer, as the cancer cells have not shown invasive growth, the patient can be treated by breast-conserving surgery, after which the lesion can be cleared and the probability of recurrence is relatively low, so radiotherapy is not needed for the time being. 2. Radiotherapy is needed: if the patient’s situation is more serious and belongs to middle or late stage breast cancer, after breast-conserving surgery, due to the relatively small scope of excision, there is a chance of recurrence, and radiotherapy is needed at this time to minimize the probability of recurrence and metastasis of cancer cells. If the tumor is large in size, there is also a risk of recurrence and radiotherapy treatment is also needed. After breast-conserving surgery, patients need to follow the doctor’s instructions for further treatment. Whether radiotherapy or other treatments are needed, the next treatment plan should be guided by a professional doctor after giving relevant assessment.