Breast conserving therapy (BCT) has become the standard of care for treating early-stage breast cancers based on six prospective randomized trials with 20 years of follow-up data (Fisher). During lumpectomy, the surgeon removes the tumor and a surrounding rim of normal tissue (margin), leaving surgical clips to help designate the resection bed. Radiation treatment is directed at the whole breast for 5 1/2 weeks and is generally followed by a 1-2 week boost directed at the lumpectomy site plus a margin of normal breast tissue. The benefit of adding the tumor bed boost, (TBB) has been shown in two studies to decrease local failures [Romestaig; Bartelink].