 This is a non-randomized Phase I-II feasibility study of partial breast irradiation with accelerated IMRT technique. In this study, patients will be eligible if the estimated risk of breast cancer elsewhere in the breast beyond the tumor bed is low. The radiation treatment will be available to women who are older than 40 years, have a DCIS Ductal carcinoma in situ or T1, N0, M0, AJCC classification, version 6.0, non-lobular infiltrating carcinoma treated with breast-conserving surgery. 