The Effectiveness of Colloidal Thorium Dioxide as an Internal Alpha Emitter: A Combined Morphologic and Radioautographic Study ‡

The hazard of ionizing radiation from internally administered colloidal thorium dioxide (Thorotrast) has been a subject of controversy even since this medium was first employed in clinical roentgenology. Reports of neoplasia as well as diffuse hepatic fibrosis occurring in patients following Thorotrast administration have been summarized and evaluated by Thomas et al.7 Although intravenous injection of colloidal thorium dioxide introduces a highly potent source of intense alpha radiation into certain tissues of the body, a combined histologic and radioautographic study clearly indicates that the tissues are exposed to but a fraction of the total ionization dosage and that most of the radiation energy is dissipated within the thorium deposits themselves.