Chromosome Aberrations in Peripheral Blood Cells in Man Following Chronic Irradiation from Internal Deposits of Thorotrast

The in vivo production of chromosome aberrations in the peripheral leukocytes of individuals subjected to X-ray, y-ray, and neutron irradiation has been demonstrated by several investigators. To date, such observations have been reported in the cases of persons X-rayed for diagnostic reasons (1-4), personnel subjected to occupational exposure (5, 6), patients therapeutically irradiated (7-11), and individuals accidently exposed to radiation (6, 12, 13). In contrast to these observations on the effects of acute external irradiation, the present study concerns a group of patients who have been subjected to chronic internal irradiation over the course of many years. The radiation in these cases is derived from isotopes of the Th232 decay series, administered in the form of Thorotrast-a commercial preparation of thorium dioxide which was introduced as a contrast medium for radiography in 1931. Because of its ease of administration and its excellent contrast properties, it was widely used for several years in arteriography, and to a lesser extent for other applications such as retrograde pyelography. It came into disrepute, however, around 1945 after warnings of its possible toxic effects had appeared in the literature, and its use as a contrast medium in routine radiography has since been largely discontinued.