NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,800 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.

radioactive seed
(RAY-dee-oh-AK-tiv...)
A small, radioactive pellet that is placed in or near a tumor. Cancer cells are killed by the energy given off as the radioactive material breaks down and becomes more stable.

EnlargeRadioactive seeds; drawing shows a gloved hand using an instrument to pick up small, radioactive seeds.

Radioactive seeds. Small, radioactive seeds may be placed in or near a tumor to kill cancer cells.