Additional Study Information: This study is for women who have been diagnosed with stage 2 or stage 3 breast cancer whose doctor has recommended that you receive radiation therapy after your mastectomy to prevent your breast cancer from coming back. Radiation uses particles of energy to kill any remaining cancer cells where your breast was removed or in the lymph nodes. Radiation after mastectomy has been shown to reduce the number of patients whose breast cancer returns. Women with cancer in their lymph nodes after mastectomy have been shown to live longer when they receive radiation therapy. Radiation treatments are given daily, Monday through Friday, to breast cancer patients over a treatment course of 5 to 6 weeks. In this study we will determine whether a short-course radiation therapy option (3 to 4 weeks) after mastectomy is as safe and effective in the setting of breast reconstruction as the usual 5 to 6 week treatment course. Short-course radiation therapy is also called hypofractionated radiation. This study will also examine whether a shorter course of radiation therapy will lower treatment costs and improve patient satisfaction.