Brachytherapy, also known as internal radiation, is a form of radiation therapy, a technique used to treat cancer. In radiation therapy, high-energy waves and/or particles, such as X-rays and gamma rays, are used to kill cancerous cells. This form of therapy can be used in conjunction with chemotherapy and surgical treatments. In brachytherapy, radioactive material is placed into the body cavity or tissue near the cancer to kill the cells. In intraoperative brachytherapy, this treatment occurs when the tumor in question is open to the environment during surgery.