Electron Transport in Tissue-like Material

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DESCRIPTION (provided by applicant): This proposal is a revised competitive renewal of a three year grant initiated in July, 2002. The proposed study of electron emission from thin foils is designed to provide data to test computational models developed to describe the initial spatial pattern of energy deposition by ionizing radiation in biologic material. These initial damage patterns affect subsequent chemistry and biochemistry that influence crucial cellular pathways leading to biological repair, genomic instability, apoptosis, and/or finally cancer induction. Much of our knowledge of the initial patterns of radiation damage is obtained from event-by-event Monte Carlo track simulation models that often contain uncertainties in their cross section database. The current work, and the proposed extension, provides data on which we can test track simulation models at the level of the physics of electron transport, i.e., prior to modification and averaging by chemical reactions. During the initial grant period data have been obtained for electron transport in water, a major constituent of tissue; SF6, a unique molecule with well defined structure in the low-energy electron transport spectra; and preliminary data have been obtained for several molecules that aid in assessment of effects of surfaces bonding and molecular structure on electron spectra, e.g., data have been derived from solid (frozen) CO2, C2H6, C3H6, C2F2H2, and Xenon. Continuing study of hydrocarbons is underway and target technology is being developed to extend this work to larger bio-molecules and tissue. The cryogenic target provides a unique capability to study bio-molecules and tissue as a function of temperature and thereby as a function of water content. A major goal of the continued work is to better understand the role of water in the transport of electrons in bio- molecules and tissue. We feel this expanded study will provide unique insight into the role of tissue constituents on electron transport, and provide data that can provide sensitive tests of evolving models of electron transport following energy deposition by ionizing radiation. This work will contribute to increased accuracy in the assessment of local dose distributions delivered to cells, cellular components, and critical biomolecules. The results will enhance our effort to establish clinically relevant radiation treatment with a better understanding of potential damage to healthy tissue.