Primary liver cell carcinoma 24 years after intravenous injection of thorotrast.

Thorium dioxide, when injected intravenously, is taken up by the reticulo-endothelial system and retained indefinitely, rendering the liver and spleen radio-opaque (Radt, 1930). A 25% colloidal solution of thorium dioxide was marketed under the name of "thorotrast" and used not only for hepatolienography but for retrograde pyelography, bronchography, and angiography generally, not to mention other uses, e.g., cerebral 'ventriculography, arthrography, mammography, dacrocystography, antral visualization. From the outset its tumour-forming potentialities were recognized (Stewart, Einhorn, and Illick, 1932), and the American Medical Association (1932) recommended that intravenous administration be discontinued, but for some years "' thorotrast" was used by those who held that its radioactive properties were negligible. The conflicting claims were reviewed by Rigler, Koucky, and Abraham (1935) and by Orr, Popoff, Rosedale, and Stephenson (1938). Injected into animals, "thorotrast" induces sarcomata after a latent pzriod (Roussy, Oberling, and Guerin, 1934; Selbie, 1936). By means of the Geiger counter Taft (1937a) was able to show that the standard dosage for human hepatolienography (75 ml.) gives a gamma radiation equivalent to 1.37 micrograms of radium.* Reeves and Stuck (1938) observed that retention of "thorotrast" in the reticulo-endothelial system affords a continuous opportunity for the damaging effects of alpha radiation. These rays have a higher relative biological efficiency than beta or gamma rays, and their activity is extremely localized. The emission of alpha particles in rabbits injected with " thorotrast" was studied under the spinthariscope by Orr et al. (1938).