[Radiation exposure in x-ray mammography].

When discussing the radiation risk of X-ray mammography, the magnitude of the dose applied has decisive importance. The radiation exposure of the breast is the predominant factor in risk considerations, since it contributes more than 98% to the effective dose of this examination. At present, it is generally assumed that, with regard to cancer induction by ionizing radiation, the glandular tissue is the most vulnerable part in the breast. Therefore, the average glandular dose, i.e., the mean value of the absorbed dose in the glandular tissue, is used for a description of the radiation risk. The average glandular dose cannot be measured directly, but is calculated under certain assumptions from the experimentally determined entrance surface air kerma or entrance surface dose by the use of a so-called conversion factors. During the seventies, i.e., in the era of the industrial type X-ray film, the mean value of the average glandular dose per exposure for a larger sample of patients (n > 100) was about 20 mGy. Due to the progress in radiographic technique such as, for example, the use of sensitive film-screen systems, optimized radiation qualities and modern automatic exposure control units this value has now decreased to about 1 mGy. Further dose reductions seem possible by the introduction of digital image receptors.