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Objective:To establish optimal beam distribution of intensity-modulated radiation therapy (IMRT) for patient after breast-conserving surgery.Methods: We developed five IMRT plans of different beam distribution for each of 30 patients following lumpectomy.In the 30 patients, 15 patients was suffered left breast cancer, and 15 patients was suffered fight breast cancer.A dose of 50Gy was prescribed to the planning target volume(PTV).Five IMRT plans used inverse-planned techniques, and the same cost function (constraint condition) was used for each IMRT plan.Five IMRT plans respectively were 2-field, 3-field, 4-field, 5-field and 8-field.Beside conformal index (CI), homogenity index (HI) , dose-volume histograms (DVHs) were generated and compared, and metrics chosed for comparison were analyzed using the paired t test.Results:In the five IMRT plans, 8-field IMRT could achieve the best CI but mean--while increased dose exposed on heart, contralateral lung, cord and extended low-dose (<2000cGy) region in ipsilateral lung.2-tangential fields IMRT was a perfect method for PTV being "small curvature", and protected heart,contralateral lung, cord and shrinked low-dose (<2000cGy) region in ipsilateral lung at the largest degree.But the 2-tangential fields IMRT developed easily "hot point" at internal mammary and axilla, especially when the degree of PTV curvature was increasing.3-field IMRT was the worst mothed when looking at HI.4-field and 5-field IMRT were widely-used motheds whatever the shape of PTV.Exposure to ipsilateral lung in five IMRT methods, at the less than 2000cGy (V5,V10,V15) range, allps were less than 0.05, and at the more than 2000cGy (V25,V30,V35,V40,V45) range, only threeps were less than 0.05.Conclusions: When we design IMRT plans for patients following lumpectomy, 2-tangential fields IMRT plan is firstly tested.If not, 4-field and 5-field IMRT were too available methods for whatever the shape of PTV.