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(RAY-dee-AY-shun THAYR-uh-pee)
![](https://webarchive.library.unt.edu/eot2008/20080925101157im_/http://www.cancer.gov/images/spacer.gif)
| The use of high-energy radiation from x-rays, gamma rays, neutrons, protons, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy). Systemic radiation therapy uses a radioactive substance, such as a radiolabeled monoclonal antibody, that travels in the blood to tissues throughout the body. Also called radiotherapy and irradiation. |
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