Partial Breast Irradiation (PBI) Using 40 Gy for Select Patients With Early Invasive or Noninvasive Breast Cancer

Currently the standard of care is to treat early stage invasive breast cancer or ductal carcinoma in situ (DCIS) with a combination of lumpectomy and radiotherapy, known as "breast-conserving therapy" (BCT). The traditional method of giving radiation therapy after a lumpectomy is to the whole breast. However the investigators do not know if the whole breast needs to be receive radiation to better control your cancer or only a more limited area of the breast surrounding the tumor. The purpose of this study is to see the side effects of delivering partial breast irradiation (PBI) instead of whole breast irradiation (WBI). PBI is radiation therapy given only to the area of the breast where the cancer was removed. Another purpose of this study is to look long term at the rate at which cancer comes back in the same breast after PBI. WBI is radiation therapy given 5 days a week for 5 to 7 weeks to the whole breast. Partial breast irradiation radiation therapy (PBI) is much shorter than whole breast irradiation. The investigators propose to deliver the PBI radiation therapy, for a few minutes a day, once a day, five days a week, for 2 weeks. In this study the investigators will learn about the good and bad effects of PBI radiation therapy. In this study, the investigators will also learn about how the breast looks after surgery and radiation therapy.