Biophysical investigations of the dose-effect relationship in chromosome aberrations of human lymphocytes caused by thorotrast deposits. II. Biological and medical aspects.

The biological effect of alpha-radiation, which has been examined in this investigation, is the occurrence of chromosome aberrations in lymphocytes from the peripheral blood of Thorotrast patients. To set up a dose-effect relationship, it is necessary to estimate the absorbed dose of a single lymphocyte found in a blood sample. Then it would be possible to use chromosome aberrations of lymphocytes from peripheral blood as an indicator for estimating the effective radiation dose. The physical aspects of this investigation have been described in part I of this paper. In part II, biomedical considerations are described and discussed. The irradiation of the lymphocytes takes place in the whole lymphatic system, but the lymph node could have been used as a model for the lymphatic system. Based on the evaluation of size and distribution of Thorotrast conglomerates, the average annual dose in different structures of the lymph node has been determined. The Thorotrast content in lymph nodes depends on the region of the body from where the lymph nodes originate. It has been tried to compile the distribution of the lymph nodes in the different regions of the body. Annual doses have been calculated in these different regions in order to find a representative value for the whole body. The values describing the kinetics of the lymphocytes in the body have been used to convert the annual dose in lymph nodes into the dose of a lymphocyte found in a sample of peripheral blood. It is pointed out that the calculated dose of the lymphocytes, being 250 rad, is an estimation of an upper value. The lymphocytes are "in vivo" irradiated by the Thorotrast, but most of the calibrations used for biological dosimetry are referred to as "in vitro" experiments. The discrepancy between "in vivo" and "in vitro" results are discussed in the findings of this study and in other results.