No post-surgical radiotherapy is indicated after radical surgery for stage I breast cancer. stage II breast cancer patients with negative axillary lymph nodes are not treated with radiotherapy, and it is controversial whether to treat 1-3 axillary lymph node metastases with radiotherapy. However, some studies have shown that radiotherapy can also increase the effectiveness of local control and systemic control. All stage III breast cancers require radiotherapy, but the field of radiation therapy is different. If the lymph nodes are negative, only the chest wall is irradiated; if there are 1-3 metastases in the axillary lymph nodes, the supraclavicular and chest wall are irradiated; if there are more than 4 metastases or metastases in the subclavicular lymph nodes, the chest wall, internal breast area and supraclavicular are irradiated. However, for those who have residual lesions in the axilla that are difficult to be removed surgically by more than 2 cm, or for those who have cancer thrombosis in the axillary vessels, additional axillary irradiation can be added. The above is a very detailed principle of radiotherapy, but only very experienced doctors should remember it very clearly in the specific clinical application, while general clinicians only give advice according to the patient’s condition. However, for some physicians, the above mentioned principles are not as clear as they should be. However, the above principles are very difficult for some doctors to remember, and they are summarized as follows: 1. lymphatic vessels or intravascular cancer thrombus formation, which is actually some special cases; 4, surgery is difficult to achieve the purpose of radical treatment, and there is residual at the edge.