Radiation therapy

High-energy x-rays, gamma rays, neutrons, and other sources of radiation are used to kill cancer cells and shrink tumors. Radiation coming from a machine outside the body is referred to as external radiation therapy or external-beam radiation therapy. Radiation may also come from materials that produce radiation called radioisotopes. Radioisotopes can be inserted in or near the cancerous cells or tumors; this type of radiation therapy is called internal radiation therapy, implant radiation, interstitial radiation, or brachytherapy. Systemic radiation therapy, also referred to as radiotherapy, irradiation, and x-ray therapy, uses a radioactive substance, such as a radiolabeled monoclonal antibody, that circulates throughout the body.