Radiotherapy (radiation therapy) is a form of treatment frequently applied in the breast cancer. It is applied to provide local regional control in the breast cancer. It is applied by radiation oncologist specialists with special technological devices. The treatment mechanism works by destroying cancer cells or disrupting the DNA structure of the cells. 

In order to prevent recurrences in the remaining breast tissue in the patients who have undergone the breast conserving surgery and in some special conditions (in cases where the tumor covers the skin or chest wall before the operation, in cases where there are 4 or more cancerous glands under the axillary fossa, the tumor size is large, etc.) in the patients with mastectomy, radiation therapy is applied. Sometimes it can be used in bone metastases and for the pain treatment. Today, there are radiotherapy methods applied only to the tumor periphery, not to the whole breast, in a limited group of selected patients. This can be done during surgery (intraoperative radiotherapy) or after the surgery. 

Radiotherapy is usually administered within the first 6 months after the surgery after chemotherapy treatment is completed. It is one of the treatments with mild side effects that do not require hospitalization, which lasts an average of 5-6 weeks.