Inclusion Criteria:  Pathologic diagnosis of stage I-IIIc invasive breast cancer (ductal, lobular, mammary, medullary, or ductal)  ≤ T3 or N+  negative surgery margins positive postoperative pathologic axillary lymph nodes after neoadjuvant chemotherapy (ypN+). Undergo mastectomy+expander+RT（hypofractionated radiotherapy）+delayed prosthesis reconstruction Sign the informed consent form  Exclusion Criteria:  T4, axillary sentinel lymph node biopsy without axillary dissection Recurrent breast cancer or history of prior breast radiation therapy (neck, chest wall, axilla) Uncontrollable co-morbidities, including but not limited to active collagen vascular disease (e.g., systemic lupus erythematosus, scleroderma, or dermatomyositis), persistent or active infection, symptomatic congestive heart failure, unstable angina, mental illness incapacitating participation in this study Pregnancy or breastfeeding History of malignancy other than the following： (At least 5 years of tumor free survival with a very low risk of recurrence, e.g., carcinoma in situ of the cervix and basal cell or squamous cell carcinoma of the skin） requiring bilateral breast/chest wall radiation therapy