Radiation therapy, also called radiotherapy, is the use of high-energy rays to kill cancer cells. The radiation can be directed at the breast by a machine (external beam radiation), or it can come from radioactive material in thin plastic tubes that are temporarily placed into the breast (brachytherapy, a form of accelerated partial breast radiation therapy).
For external radiation therapy, the patient goes to the radiation facility for her treatment, generally five days a week for several weeks. For accelerated partial breast radiation therapy, a patient comes to the radiation facility twice a day for five days, and the catheter is removed from the breast after the treatment is completed. Radiation therapy generally follows breast-sparing surgery, such as lumpectomy or partial mastectomy. Sometimes, depending on the size of the tumor and other factors, radiation therapy is also administered after mastectomy to kill any breast cancer cells that remain in the area.