DCIS is the name for a condition in which abnormal cells are contained within the milk ducts of the breast. DCIS is not an invasive breast cancer however, if left untreated, DCIS has the potential to turn into an invasive breast cancer. This is why we treat DCIS to reduce the risk of developing invasive cancer. Radiation treatment after surgery for DCIS improves the chances of not developing further cancer in that breast. However, this treatment does not completely cure everyone who has it. In some people DCIS comes back, despite having this treatment. Doctors are looking for better ways to treat people with DCIS. In this research project, the researchers will test whether an additional dose of radiation called a boost given to the part of the breast that had DCIS within it improves the chances of not having the cancer come back in the breast.