Risk of Radiation Carcinogenesis - Semantic Scholar

Risk of Radiation Carcinogenesis Francis A. Cucinotta NASA Johnson Space Center Marco Durante GSI Germany

Occupational radiation exposure from the space environment may increase cancer morbidity or mortality risk in astronauts. This risk may be influenced by other space flight factors including microgravity and e nvironmental contaminants. A M ars mission will not be fe asible unless improved shielding is dev eloped or tran sit time is decreased. – Human Research Program Requirements Document, H RP-47052, R ev. C , dated Ja n 2009.

Pictured is the Crab Nebula, a 6-light-year-wide expanding remnant of the supernova explosion of a star; the colors indicate the different expelled elements. Astronauts in space are exposed to protons and high-energy and charge ions that are released by events such as supernovae, along with secondary radiation, including neutrons and recoil nuclei that are produced by nuclear reactions in spacecraft and tissue. Ground studies and system biology models of cancer risk reduce uncertainties in risk projection models and pave the way for biological countermeasure development to protect astronauts on future Exploration missions.

Risk of Radiation Carcinogenesis

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Risk of Radiation Carcinogenesis

Human Health and Performance Risks of Space Exploration Missions

Chapter 4

Executive Summary Astronauts who are on missions to the ISS, the moon, or Mars are exposed to ionizing radiation with effective doses in the range from 50 to 2,000 mSv (milli-Sievert) as projected for possible mission scenarios (Cucinotta and Durante, 2006; Cucinotta et al., 2008). The evidence of cancer risk from ionizing radiation is extensive for radiation doses that are above about 50 mSv. Human epidemiology studies that provide evidence for cancer risks for low-linear energy transfer (LET) radiation such as X rays or gamma rays at doses from 50 to 2,000 mSv include: the survivors of the atomic-bomb explosions in Hiroshima and Nagasaki, nuclear reactor workers (Cardis et al., 1995; 2007) in the United States, Canada, Europe, and Russia, and patients who were treated therapeutically with radiation. Ongoing studies are providing new evidence of radiation cancer risks in populations that were accidentally exposed to radiation (i.e., from the Chernobyl accident and from Russian nuclear weapons production sites), and continue to analyze results from the Japanese atomic-bomb survivors from Hiroshima and Nagasaki. These studies provide strong evidence for cancer morbidity and mortality risks at more than 12 tissue sites, with the largest cancer risks for adults found for leukemia and tumors of the lung, breast, stomach, colon, bladder, and liver. There is also strong evidence for inter-gender variations due to differences in the natural incidence of cancer as well as additional cancer risks for the breast and the ovaries and a higher risk from radiation for lung cancer in females (National Council on Radiation Protection and Measurements (NCRP), 2000). Human studies also provide evidence for a declining risk with increasing age at exposure, although the magnitude of this reduction above age 30 years is uncertain (NCRP, 2000; Biological Effects of Ionizing Radiation (BEIR), 2006). Genetic and environmental factors that contribute to radiation carcinogenesis are also being explored to support the identification of individuals with higher or reduced risk. In space, astronauts are exposed to protons and high-Z high-energy (HZE) ions together with secondary radiation, including neutrons and recoil nuclei, which are produced by nuclear reactions in spacecraft or tissue. Whole body doses of 1 to 2 mSv/day accumulate in interplanetary space, and approximately half of this value accumulates on planetary surfaces (Cucinotta et al., 2006; NCRP, 2006). Radiation shielding is an effective countermeasure for solar particle events (SPEs), which are chiefly made up of protons with energies that are largely below a few hundred MeV. The intermediate dose-rates (