COLLOIDAL thorium dioxide (Thorotrast) was used extensively from 1928 until about 1950 to perform arteriograms, urograms, fistulagrams, and to outline focal lesions of the liver. The radiation dose from the amount usually injected is sufficient to warrant the expectation that neoplasms might develop in tissues chronically exposed to this agent which is almost totally retained in the body and remains radioactive for many years.
The first example of a malignant tumor in man induced by thorium dioxide was reported in 1947.1 By March of 1962, 55 well-documented examples of Thorotrast-induced malignancy in man had been reported.2-8
Recently, chelating agents have been found useful in removing heavy metals from humans. Animal and human experiments9-11 suggest that diethylenetriaminepentacetic acid (DTPA) may be effective in the removal of thorium, although there are indications that the ionic form of thorium would be more susceptible than the colloidal form.