NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,780 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

photon beam radiation therapy
(FOH-ton beem RAY-dee-AY-shun THAYR-uh-pee)
A type of radiation therapy that uses x-rays or gamma rays that come from a special machine called a linear accelerator (linac). The radiation dose is delivered at the surface of the body and goes into the tumor and through the body. Photon beam radiation therapy is different from proton beam therapy.