Assessment of radiosensitivity and biomonitoring of exposure to space radiation

Abstract

Unlike individuals on Earth who are protected against most types of ionizing radiation by the shielding characteristics of the atmosphere and the electromagnetic field, astronauts aboard a spaceship or on the surface of the moon or another planet are exposed to much higher doses of ionizing radiation. Besides this, the radiation spectrum present in space is very different from that on Earth (see Chap. 20). Terrestrial radiation mainly consists of low-LET radiation such as X- and gamma rays. Space radiation on the other hand is made up of (1) radiation from the solar wind which is trapped in the Earth’s magnetic field (Van Allen belts), (2) galactic cosmic radiation comprised of high-energy protons and heavy ions, and (3) solar particle events mainly consisting of low-energy protons. Recent estimations of the dose equivalent for a round trip to Mars were in the order of 0.66 Sv, which is well beyond the limitations for nuclear workers. Therefore, for manned spaceflight, the biological response to space radiation is of critical concern for risk assessment for astronauts, especially since space agencies like NASA limit the risk of radiation exposure-induced death due to cancer to only 3% (at 95% confidence level). Based on findings from early NASA astronauts, some of whom traveled beyond Low Earth Orbit, no association was found between radiation dose and mortality from cardiovascular disease or cancer risk using a logistic regression model. Nevertheless, for long-duration interplanetary manned missions the uncertainty about the health risks of radiation exposure remains one of the most important limiting factors. For this reason, the identification of (predictive) biomarkers to determine both the received radiation dose (biodosimetry) as well as the radiosensitivity of individuals may be an important aspect for future crew selection. This chapter reviews some of the most frequently used assays for these purposes.