(external beam radiotherapy) n. a form of *radiotherapy in which penetrating radiation is directed at a patient from a distance. Originally radium was used as the radiation source; today artificially produced X-rays are predominantly used. See linear accelerator.
n. a metallic element. The artificial radioisotope cobalt-60, or radiocobalt, is a powerful emitter of gamma radiation and is used in the radiation treatment of cancer (see radiotherapy; teletherapy). Cobalt itself forms part of the *vitamin B12 molecule. Symbol: Co.... cobalt
n. therapeutic radiology: the treatment of disease with penetrating radiation, such as X-rays, beta rays, or gamma rays, which may be produced by machines or given off by radioactive isotopes. Beams of radiation may be directed at a diseased part from a distance (see teletherapy), or radioactive material, in the form of needles, wires, or pellets, may be implanted in the body (see brachytherapy). Many forms of cancer are destroyed by radiotherapy.... radiotherapy
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