Organ Dose Measurements Using Phantom Torso

The key to assessing the radiation risk is the estimation of organ level dose equivalent. Current experimental methods do not measure organ level dose, except in the case of skin. The organ level dose is only calculated from radiation environment model using appropriate radiation transport model(s) that transport the incident spectrum through both spacecraft shielding distribution and anatomical male or female models. The accuracy of these transport models through material is not quite established and can vary from 15 to 50 % for dose and dose equivalent, and up to factors of 2 - 5 for the LET (Linear Energy Transfer) spectrum. In addition, these models do not adequately describe the LET distribution from target nuclei and neutron production. The neutrons can add a significant contribution to dose equivalent in human body because of large amount of water. Also, at bone-tissue interface, high LET particles can lead to significant radiation damage. We propose to measure the dose, the dose equivalent, and the LET spectra for both trapped and galactic cosmic radiation using a phantom torso in Space Shuttle flights. The torso will be heavily instrumented to provide these measurements at key organs. As part of this experiment, we propose, during the first year, to develop a small solid state dosimeter to measure the dose and dose equivalent rates, as a function of mission elapsed time. This proposed experiment, with ground based studies with human fibroblasts and proton beams, and analytical radiation transport modeling will provide a critical needed set of organ level radiation risk and help in validating radiation transport models.