Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 64

A bioassay program internally monitors the deposited radionuclides. Two different, complementary bioassay techniques are employed to determine the internally deposited radioactivity. In vivo bioassay means direct determination of internal radionuclides by scanning the whole body, or a selected part of the body, with a sensitive detector. This method is useful only for gamma‐emitting radionuclides or high‐energy beta emitters that generate bremsstrahlung within the body. In vitro bioassay involves the analysis of body fluids, excreta, and exhaled air for the purpose of estimating the original intake. Although a single measurement may suffice for determining whether or not radioactivity is present in the body, generally, repeated measurements are necessary if one wishes to achieve the best estimate of the intake and of the dose.

The rationale underlying the practice of in vitro bioassay is that a quantitative relationship exists among inhalation or ingestion of a radionuclide, the resulting body burden, and the rate at which the radionuclide is eliminated. From measurements of radioactivity in urine or feces, therefore, one should be able to infer the body burden, and thus estimate the radiation dose. Unfortunately, the kinetics of metabolism in any particular person is influenced by many factors, resulting in a great deal of uncertainty about the exact quantitative relationships among elimination rates, body burden, and radiation dose. In most instances, therefore, bioassay data allows only a reasonable estimate of the intake and dose.