There are two types of APBI: EBRT (intraoperative electron beam radiation therapy and intensity modulated radiation therapy) and brachytherapy (BT; interstitial and intracavitary). In EBRT, APBI source of radiation is external to the patient, while in BT it is placed inside or near the tumor.All these techniques will be studied and compared with each other and standard whole breast irradiation in an upcoming National Surgical Adjuvant Breast and Bowel Project (NSAPB) Radiation Therapy Oncology Group (RTOG) study. All APBI techniques allow definition of the highest risk area of the breast and delivery of highly focused radiation to this smaller, more precise area of the breast.The advantage of APBI is greater specificity of the delivered dose, which allows for optimizing the cosmetic appearance of the breast and avoids potentially painful fibrosis and necrosis. The scientific rationale for APBI is based on the finding that the vast majority of recurrences after lumpectomy occur in the tumor bed region, with only 1% to 6% incidence of remote (far away or elsewhere in the breast) failures, therefore whole breast radiation therapy may not be needed in appropriately selected patients. However, as the breast is attached to the chest wall, the target area in the breast can be subject to motion related to respiration.This can have the unwanted side effect of making it necessary to identify an even larger area before treatment, and therefore losing some of the advantage of these APBI over the standard whole breast radiation.