Early-stage breast cancer patients treated with breast conservative surgery are enrolled in this study if they meet defined criteria. Patients are randomized into two groups: conventional fractionation radiotherapy and hypofractionated radiotherapy.The hypothesis is that conventional fractionation radiotherapy and hypofractionated radiotherapy have similar efficacy and toxicity.

Inclusion Criteria:

1. KPS>=60
2. histology confirmed invasive breast cancer
3. received breast conservative surgery(wide local excision and axilla dissection, or axillary sentinel node biopsy if sentinel node is negative)
4. surgical margins negative
5. primary tumor ≤5cm in the largest diameter
6. no internal mammary node or supraclavicular node metastases or distant metastasis
7. can tolerate chemotherapy,hormone therapy (if needed) and radiotherapy
8. for patients not need chemotherapy，enrollment date is required no more than 8 weeks from surgery date
9. for patients with chemotherapy first,enrollment date is required no more than 8 weeks from the last date of chemotherapy
10. patients signed written inform consent form

Exclusion Criteria:

1. ductal carcinoma in situ
2. prior neoadjuvant chemotherapy
3. prior breast cancer history
4. bilateral breast cancer
5. pregnant or during lactation
6. prior or concomitant malignant tumor excluded skin cancer(not malignant melanoma) and cervix carcinoma in situ
7. active collagen vascular disease
8. prior neoadjuvant hormone therapy
9. immediate ipsilateral breast reconstruction