Measurement of thorium isotopes and 228Ra in soft tissues and bones of a deceased Thorotrast patient

The whole body of an individual injected with Thorotrast 36 y prior to her death was analyzed for 232Th, 228Ra, 228Th, and 230Th. Measurement of these isotopes in all tissues of the body will provide data necessary to caculate the radiation dose to individual tissues and to evaluate the risk potential associated with deposition of thorium and progeny in humans. The tissues were ashed, dissolved in acid, and the thorium isolated by ion exchange and electrodeposition. The 228Ra was determined by measuring the 0.991-MeV gamma rays associated with decay of the 228Ac daughter. It was estimated that almost all of the 232Th from the original injection was retained in the body, mostly in the tissues of the reticuloendothelial system. A total of 28 kBq (0.76 microCi) of 232Th was measured in the soft tissues and bones. The body also contained 13 kBq 228Ra, 12 kBq 228Th, and 3.9 kBq 230Th. A Thorotrastoma contained about 3.5% of the total activity. Excluding the Thorotrastoma, approximately 45% of all the activity (232Th, 228Ra, 228Th, and 230Th) was retained in the liver, 13% in the spleen, 2% in muscle, 1% in skin, slightly less than 1% in the respiratory tract, 4% in all other soft tissues, and 33% in the skeleton (bone and bone marrow). Sixty to 80% of the thorium activity in bones containing red marrow was located in the marrow. Bones containing yellow marrow had less than 40% of the thorium activity in the marrow. Highest concentrations were found in the hepatic and other abdominal lymph nodes, spleen, hilar lymph nodes, liver, trachea, and bone. Approximately 60% of the 228Ra formed from the decay of the 232Th had been excreted from the body. The 228Ra and 228Th were in approximate equilibrium throughout the body.