Radiotherapy uses pulses of radiation to destroy cancer cells. Depending on the stage of the disease and other factors, radiation therapy may be recommended after surgery to help lower the likelihood of recurrence in the same breast or nearby lymph node. It may also be recommended for patients who undergo mastectomy, especially if the size of the tumour was big, or if cancer was present in the lymph nodes, skin, or muscle surrounding the tumour. It may also be used if the cancer has spread to other parts of the body, such as the bones, spinal cord, or brain.