【Abstract】 Objective To observe the dose distribution, adverse reaction, cosmetic effect and curative effect of postoperative radiotherapy using tumor bed boost simultaneously for breast cancer patients after breast conserving surgery.Methods 43 patients with Ⅰ to Ⅱ breast cancer accepted breastconserving surgery and sentinel lymph node biopsy±axillary lymph node sweeping surgery were involved. Intensitymodulated whole breast irradiation (WBI) ± supraclavicular/axillary area radiation were conducted with tumor bed boost simultaneouslyA dose of 50Gy/25f was delivered to planning target volume (PTV), and 60Gy/25f/24Gy/fx was delivered to tumor bed boost area (PGTV). Radiotherapy dosimetry characteristics, clinical adverse reaction, the cosmetic effect and curative effect were observed before and/or after radiotherapy. Results The CI, HI and dose distribution were satisfied using IMRT technique. 539% patients developed grade Ⅰ skin injury, 4186% for grade Ⅱ, 465% for grade Ⅲ, and no grade Ⅳ skin injury was found. Grade Ⅰ lung injury was 3023%, 916% for grade Ⅱ, and no grade Ⅲ or grade Ⅳ lung injury was foundGrade Ⅰ and grade Ⅱ. The upper limb lymphedema were observed in 186% and 465% patients respectivelyIn cosmetic effect evaluation. 9302% patients scored good and very good before radiation therapy, and the percentage changed to 8604% when 1 year after radiation therapy. The 3year LRFS was 9767%, and 3year OS 9535%.Conclusion In this research, the simultaneous tumor bed boost postoperative radiation therapy shows satisfied CI and HI when IMRT technique is supplied, and much more shorter treatment cycle compared with the sequential tumor bed boostIts acute and longterm side effects is lowmsked, and exhibits fine cosmetic effect. 3year LRFS and 3year OS which are no less than those in previous reports.