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NASA's Biomedical Critical Path Roadmap defines the carcinogenic risks of radiation exposure as one of only four Type I risks identified. A type I risk represents a demonstrated, serious problem with no countermeasure concepts, and may be a potential "show-stopper" for long duration spaceflight. Estimating the carcinogenic risks for different tissues in humans exposed to heavy ions is difficult at present. These ions contribute significantly to the dose and dose-equivalent received by astronauts during extended missions in low earth orbit (shuttle and ISS) and will be even more important for interplanetary excursions or lunar missions. Space radiation environments are unlike any on earth. It is a significant challenge to estimate the biological consequences of human space flight because of the heterogeneous nature of the radiation fields, which include all charged particle species from protons through uranium at varying energies of up to tens of GeV/amu. High atomic mass (Z) and high energy (HZE) particle irradiation is of particular concern because the limited experimental data to date indicate the relative biological effect (RBE) for carcinogenesis for individual densely ionizing HZE particles is several-to-many fold greater than sparsely ionizing radiation like X-rays or g-radiation. Uncertainties arising from physical issues such as charged particle fragmentation in shielding and in human tissue and environmental issues such as prediction of solar particle events confound NASA's ability to predict the carcinogenic risks associated with space flight. These uncertainties are compounded further by our presently incomplete understanding of carcinogenesis. |
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SPECIFIC AIMS
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