Elimination of Radioactive Elements by Patients and Rabbits after Injection of Thorotrast

Since thorotrast has been found useful as a contrast medium, it is of considerable interest to find out how thorium and its products are distributed in the body and to what extent these radioactive elements are eliminated. The danger from the continued exposure of the tissues to the emitted alpha, beta, and gamma rays makes such information still more important. It is well known that thorotrast is absorbed rapidly by the reticulo-endothelial system and deposited for the most part in the liver and spleen. Previous studies by other investigators have contributed much information and have proved that the thorium remains long in these tissues. Pohle and Ritchie (1) report that the roentgen ray shadows cast by livers of rabbits, in which thorotrast was deposited, decreased slightly after considerable periods of time. Rigler (2) states that in man there is a noticeable decrease in the density of livers containing thorotrast after intervals of several years. This may be due to a redistribution of the thorium, as neighboring lymph nodes during the same period increase in density. Reeves and Morgan (3) have shown, by means of Geiger-Muller counter methods, a probable gradual decrease of the thorium content of the reticulo-endothelial system noticeable only over a period of years. Leipert (4, 5) found at autopsy about 60 per cent of the thorium in the liver and spleen of two patients who died a few days after injection. He found 97 per cent in the same organs at autopsy of a patient who had a bile duct block and died about sixty days after the injection of thorotrast. Jacobson and Rosenbaum (6) found 27 per cent thorium dioxide present in the ashed liver of a patient injected with thorotrast five years previous to death. At this hospital we have measured the gamma-ray activity from living patients by means of a Geiger-Müller counter, six or seven years after the injection of thorotrast. We obtained counts from the region of liver and spleen corresponding to about 20 per cent of the activity of the injected material. Wichmann and Fricke (7) examined the urine, by chemical and electroscopic means, of a patient who had been given thorotrast, without finding any trace of thorium or radioactivity. Leipert (4) investigated the blood, urine, and feces of dogs after thorotrast had been injected. No trace of thorium was found. Leipert carried out a number of experiments with rabbits and determined the distribution of the thorium dioxide in different organs after different time intervals. From 58 to 75 per cent of the amount injected was recovered in the liver and spleen. The first animal was killed one day after injection and the last one 477 days after injection. The fluctuations in amount found showed no correlation with the elapsed time. Some thorium dioxide was also recovered from bone marrow, kidneys, and lungs. Per gram of tissue the liver and bone marrow contained about the same amount and the spleen about ten times as much.