This is a phase II study. In patients with node-negative invasive breast cancer or carcinoma in situ treated by breast conserving surgery, postoperative whole breast irradiation with inversely intensity modulated radiotherapy and a simultaneous integrated boost is technically feasible. The aim of this study is to evaluate the radiation toxicity, cosmetic outcome and local control rate in a single center

Inclusion Criteria:

• Eastern Cooperative Oncology Group performance score﹤2
• All patients aged >18 years and < 70 years after breast conserving surgery.
• On histological examination, the tumor must be DCIS or invasive adenocarcinoma of the breast.
• Negative nodal status determined by sentinel node biopsy, or axillary dissection. Axillary staging is not required for patients with DCIS
• No evidence of distant metastasis
• Gross disease may be unifocal or multifocal with pathologic (invasive and/or DCIS) tumor size excised with negative margins（>2mm）
• Surgical treatment of the breast must have been lumpectomy. Re-excision of surgical margins is permitted.
• The patient must consent to be in the study and must have signed an approved consent form.

Exclusion Criteria:

• Eastern Cooperative Oncology Group performance score≧2
• Presence of extensive intraductal component (ductal carcinoma in situ occupying > 25% of the primary invasive tumour and present adjacent to the primary tumour).Suspicious microcalcifications, densities, or palpable abnormalities (in the ipsilateral or contralateral breast) unless biopsied and found to be benign.
• Proven multicentric carcinoma (invasive cancer or DCIS) in more than one quadrant of separated.
• Metastatic disease (M1)
• Pregnancy or lactating
• Surgical margins that cannot be microscopically assessed or are positive at pathologic evaluation.
• Psychiatric or addictive disorders that preclude obtaining informed consent or adherence to protocol.
• Collagen vascular disease, specifically dermatomyositis with a CPK level above normal or with an active skin rash, systemic lupus erythematosis, or scleroderma.
• Prior breast or thoracic RT for any condition.
• Previous or concomitant malignancies except non-melanoma skin cancer, carcinoma in situ of the cervix, and invasive carcinoma of the colon, thyroid, cervix, or endometrium treated five years prior to study entry.
• Synchronous chemotherapy or target therapy is not permitted.
• Refusal of the patients to be included in the study