Hypofractionated Vs Conventional Fractionated Radiotherapy After Breast Conserving Surgery

Inclusion Criteria: * Female * Age18-70 years * Imaging examination confirmed single lesion. if the tumor is multiple, it needs to be removed by single quadrantectomy * Receive breast conserving surgery with negative margins * Axillary lymph nodes treatment: Sentinel lymph node biopsy or level I/II axillary lymph node dissection. If the sentinel lymph node is negative, the axillary lymph node dissection can be omitted. If it is positive, level I/II axillary lymph node dissection with or more than 10 lymph nodes is needed. * The tumor bed is labeled with clips and it can be drawn on the treatment planning system. * Pathologically confirmed invasive breast cancer * Pathologically stage is T1-3N0-3M0 * Immunohistochemical examination is conducted to determine the status of ER, PR, HER2, Ki67 after surgery * No distant metastases * No supraclavicular or internal mammary nodes metastases * No neoadjuvant chemotherapy * Fit for postoperative radiotherapy. No contraindications to radiotherapy * KPS≥80 * Signed informed consent Exclusion Criteria: * T4 or M1 breast cancer * Supraclavicular or internal mammary nodes metastases * Pathologically confirmed DCIS only without an invasive component * Bilateral breast cancer or historically confirmed contralateral invasive breast cancer * Treated with neoadjuvant chemotherapy or neoadjuvant endocrine therapy * Multiple lesions can not be removed by single quadrantectomy * Suspicious unresected and microcalcification, densities, or palpable abnormalities (in the ipsilateral or contralateral breast) * KPS ≤ 70 * Patients with severe non-malignant comorbidity in cardiovascular or respiration system * Concurrent or previous malignancy excluding basal or squamous cell carcinoma of the skin * Previous radiotherapy to the chest wall or regional lymph node areas * Patients with medical contraindication for radiotherapy: systemic lupus erythematosus, cirrhosis * Pregnant or lactating * Conditions indicating that the patient cannot go through the radiation therapy or follow up * Unable or unwilling to sign informed consent