The purpose of this study is to compare the efficacy and toxicities of hypofractionation radiotherapy with conventional fractionation radiotherapy in breast cancer patients treated with mastectomy.It is hypothesized that the efficacy and toxicities are similar between the two groups.

Eligible breast cancer patients with mastectomy and axillary dissection are randomized into 2 groups:conventional fractionation radiotherapy of 50 Gy in 25 fractions within 5 weeks to ipsilateral chest wall and supraclavicular nodal region,and hypofractionation radiotherapy of 43.5Gy in 15 fractions within 3 weeks to the same region.

During and after radiotherapy, the patients are followed and the efficacy and toxicities of radiotherapy are evaluated.

Inclusion Criteria:

• Ipsilateral histologically confirmed invasive breast cancer
• Undergone total mastectomy and axillary dissection
• T3-4,or >=4 positive axillary lymph nodes
• Fit for chemotherapy(if indicated),endocrine therapy(if indicated)and postoperative irradiation
• Written,informed consent
• cT3-4,or cN2, or pathological positive axillary lymph nodes during mastectomy for patients who had received neoadjuvant chemotherapy or hormone therapy
• no supraclavicular or internal mammary nodes metastases
• no distant metastases
• enrollment date no more than 8 months after surgery or no more than 2 months after chemotherapy for patients who didn't receive neoadjuvant systemic therapy.
• enrollment date no more than 2 months after surgery for patients who had received neoadjuvant systemic therapy and didn't need adjuvant chemotherapy.

Exclusion Criteria:

• Patients who undergone previous irradiation to the ipsilateral chest wall and supraclavicular region
• Previous or concurrent malignant other than non-melanomatous skin cancer
• Unable or unwilling to give informed consent
• bilateral breast cancer
• immediate or delayed ipsilateral breast cancer reconstruction