Estimate of the absorbed dose in the mouse organs and tissues after tritium administraiton

Large amounts of tritium may be used and may become a source of significant tritium release into the environment . The estimation of the accumulated dose in the human body due to tritium intake is an important subject for the protection of humans from the radiation hazard caused by internally deposited tritium. In mammals exposed to free water tritium, tritium dosimetry can be conveniently achieved by determining the tritium concentration in the body fluid, since the majority of the incorporated free water tritium is rapidly equilibrated with the body water ( 1,2,3) . In the biosphere, tritium can be converted to OBT by biological processing (4,5). The OBT taken up by humans may be incorporated into various body constituents. Some portion of the OBT is oxidized to free water tritium and equilibrates with the body water. A considerable portion of the OBT binds tightly to biological molecules and stays in the human body much longer than free water tritium (5). Establishment of practical tritium dosimetry, and determination of parameters necessary for modeling of tritium behavior in animal bodies have been main concerns in the author’s laboratory. Through the course of study some difficulty in estimating the tissue absorbed dose and determining the metabolic parameter in the mouse given tritium orally was overcome. In this report, recent development in estimating internal dose in the mouse will be mentioned. Several tritium retention models considered such a direct intake of OBT (6,7). The OBT taken into the human body distributes inhomogeneously among various organs and tissues, depending on the chemical form. For research purposes, the OBT concentration in human organs or tissues can be estimate determined by measuring the tritium content of human biopsy samples (8), blood samples and urine samples. Accurate determination of the tritium concentration in the soft tissues is difficult due to the difficulty of obtaining human tissue samples for dosimetry purpose. To cope with this problem, determination of blood tritium level was recommended from animal experiment (9).