Relative Biological Effectiveness of Tritium Beta-Particles and Co 60 Gamma-Rays Measured by Lethality in CF1 Mice

Abstract

The relative biological effectiveness (RBE) of tritium ,-radiation is of interest in establishing tolerance criteria for tritium and for relating RBE to lineal energy transfer (LET). Tritium has considerable application as a tracer for ordinary hydrogen in biological studies (1, 2) and in studies of water-exchange barriers and body water measurements (3). The application of tritium in such studies has been reviewed by Pinson (4). The maximum permissible concentration of tritium in the body and in air and water depends ultimately on the RBE value accepted for its d-radiation. Thompson reported RBE values between 1 and 2 (5), most of which were obtained from studies involving static exposure conditions produced by a constant tritium water (HTO) level in the exposure medium and thus a constant radiation dose rate. Single acute exposures of mammals to tritium result in dose rates that decrease as the concentration of HTO in body water decreases with body water turnover. Some tritium is bound to organic constituents and contributes to the radiation dose (6). This phenomenon, however, is believed to add relatively little to the total dose delivered by the concentration of HTO in body fluids required to introduce the tritium into the more stable positions (7). Effective comparison of two radiations requires that they be delivered at about the same rate. The present study was undertaken to determine the RBE of tritium A-particles and Co60 y-rays for the production of acute lethality in mice when the Co60 e-radiation is delivered at the same exponentially decreasing dose-rate characteristic of a single injection of HTO.