Estimates of
cancer risks posed to space-flight crews by exposure to high atomic number, high-energy (HZE)
ions are subject to considerable uncertainty because epidemiological data do not exist for human populations exposed to similar radiation qualities. We assessed the carcinogenic effects of 300 MeV/n 28Si or 600 MeV/n 56Fe
ions in a mouse model for radiation-induced
acute myeloid leukemia and
hepatocellular carcinoma. C3H/HeNCrl mice were irradiated with 0.1, 0.2, 0.4, or 1 Gy of 300 MeV/n 28Si
ions, 600 MeV/n 56Fe
ions or 1 or 2 Gy of
protons simulating the 1972 solar particle event (1972SPE) at the NASA Space Radiation Laboratory. Additional mice were irradiated with 137Cs gamma rays at doses of 1, 2, or 3 Gy. All groups were followed until they were moribund or reached 800 days of age. We found that 28Si or 56Fe
ions do not appear to be substantially more effective than gamma rays for the induction of
acute myeloid leukemia. However, 28Si or 56Fe ion irradiated mice had a much higher incidence of
hepatocellular carcinoma than gamma ray irradiated or
proton irradiated mice. These data demonstrate a clear difference in the effects of these HZE
ions on the induction of
leukemia compared to solid
tumors, suggesting potentially different mechanisms of
tumorigenesis. Also seen in this study was an increase in metastatic
hepatocellular carcinoma in the 28Si and 56Fe ion irradiated mice compared with those exposed to gamma rays or 1972SPE
protons, a finding with important implications for setting radiation exposure limits for space-flight crew members.