Radiotherapy for breast cancer is an important part of breast cancer treatment. Radiotherapy for breast cancer includes 2 aspects: 1. Radiotherapy after breast-conserving surgery. According to the current clinical guidelines, radiotherapy is mandatory after breast-conserving surgery, and the area of radiotherapy is the whole breast plus the axilla. Radiotherapy after modified radical surgery mainly includes the tumor bed, axillary lymph nodes, and supraclavicular fossa. If there is a combination of axillary lymph node metastasis and the number of metastasis is relatively large, preventive irradiation of the lymph node area in the supraclavicular fossa is required. If there is no axillary lymph node metastasis, the supraclavicular fossa does not need to be irradiated, which is the irradiation field. 2, the dose of radiotherapy, postoperative adjuvant radiotherapy dose is within 50GY, that is, 25 times, and then the additional dose of tumor bed, which is about 10GY, is also divided into 5 times.