Medical specialty using radioactive elements or isotopes for diagnosis and treatment of disease. A radioisotope is introduced into the body (usually by injection). The radiation it emits, detected by a scanner and recorded, reflects its distribution in different tissues and can reveal the presence, size, and shape of abnormalities in various organs. The isotopes used have short half-lives and decay before radioactivity causes any damage. Different isotopes tend to concentrate in particular organs (e.g., iodine-131 in the thyroid). Radioactive substances are also implanted to treat small, early-stage cancers. This yields a slow, continuous dose that limits damage to normal cells while destroying tumour cells. Seealso computerized axial tomography; diagnostic imaging; positron emission tomography; radiation therapy; radiology.

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