The distribution of Thorotrast in human bone marrow: a case report

Samples of bone containing cellular and fatty bone marrow were removed at autopsy from the body of a woman who, following an automobile accident, had been injected with approximately 25 mL of the radiographic contrast medium Thorotrast. The woman survived for 36 y after the accident and died at age 72 y following bone marrow failure. The samples were analyzed to determine their thorium content by x-ray fluorescence and by image analysis. In addition, Thorotrast was visualized in the different bones examined by light microscopy and by backscattered electron imaging with a scanning electron microscope. The results showed Thorotrast to be largely restricted to areas of cellular bone marrow. In such regions, Thorotrast was present throughout the marrow tissue and was also concentrated within cells that were commonly aggregated within focalized areas of the marrow. Overall the results suggest a rather uniform pattern of Thorotrast uptake by the red bone marrow at different skeletal sites. Significant deposits of Thorotrast were not found in fatty yellow marrow. We conclude that Thorotrast-derived risk estimates for human leukemia following high LET, alpha irradiation may be used for calculating the risks of alpha exposure, but with caution.