Safety Study for Short-course Accelerated, Hypofractionated Partial Breast Radiotherapy (APBI) in Women With Early Stage Breast Cancer Using the Contura MLB

Inclusion Criteria: * Life expectancy \> 10 years * Lumpectomy with clear margins (negative per NSABP criteria) * DCIS and/or invasive carcinoma * If invasive, nodes must be negative * T stage is Tis, T1 or T2\<=3 cm max diameter * ER(+) or ER(-)/PR(+) Exclusion Criteria: * Pregnant or breast feeding * Active collagen-vascular disease * Paget's disease of the breast * Prior history of breast cancer * Prior breast or thoracic radiotherapy * Multicentric carcinoma * Synchronous bilateral breast cancer * Surgical margins that cannot be assessed or that are positive * T Stage is T2\>3 cm or greater * ER(-)/PR(-)