[Epidemiological findings on health effects of medical radiation exposures].

Various epidemiological studies have been conducted in relation to medical exposures to therapeutic or diagnostic radiation. These studies provide strong evidence for increased risks of breast, thyroid, and other cancers after exposures to several Gy to several tens of Gy from therapeutic radiation. As for exposures to diagnostic radiation, however, there is much less evidence for increased risks of cancer except for those among patients with tuberculosis and scoliosis, as well as thorotrast patients who received moderate dose of radiation (approximately a hundred mGy or more) to organs or sites of interest. Epidemiological studies on medical exposures continue to provide a unique opportunity to look at the possible health effects from fractionated exposures to low to high dose of radiation which the studies of atomic bomb survivors cannot address.