Radiation therapy is a common type of treatment that aims to kill any remaining cancer cells. It is often prescribed with lumpectomy, but may be used with mastectomy. Radiation therapy often lasts a number of weeks. It is administered by board-certified physicians and technologists with technologically advanced equipment. During the therapy, radiation is directed to the breast, chest wall, and or lymph nodes from a machine located outside of the body. To optimize treatment, the patient receives doses of daily radiation for a number of weeks. Radiation therapy generally is used post-operatively in order to kill any remaining cancer cells and to reduce the likelihood of future recurrence of the cancer.