Astronaut safety in Mars exploration missions: Dynamical modeling approach to the radiogenic leukemia risk assessment

A biologically motivated dynamical model [1,2,3], which is capable of predicting the excess relative risk for radiogenic leukemia (ERRRL) among humans exposed to acute/continuous irradiation in wide ranges of doses and dose rates, is applied to estimate the ERRRL among astronauts in round-trip long-stay Mars missions. The irradiation scenarios used in the modeling studies are based on the MSL-RAD radiation environment measurements, on the characteristics of several historical large solar particles events (SPEs), and on the Mars missions design [4,5]. The dependence of ERRRL among astronauts on a vast set of the Mars mission parameters (specifically, its duration and total dose equivalent, trip-time and stay-time, presence or absence of large SPEs during trips to and from Mars, dose equivalent rates and durations of such SPEs, time intervals between SPEs, the level of shielding of radiation during large SPEs in trips to and from Mars and during staying on the Mars surface and subsurface) is thoroughly examined. Our results demonstrate that both the dynamical model [1,2,3] and a commonly used linear model (which assumes that ERRRL is directly proportional to the total mission dose equivalent D) yield nearly coinciding estimations of ERRRL in the range of applicability of the linear model. Beyond this range, the dynamical model predicts smaller values of ERRRL than those given by the linear model and the dependence of ERRRL on D becomes non-linear. The modeling findings imply that the evaluation of ERRRL among astronauts in round-trip long-stay Mars missions proceeding from the entire set of the irradiation parameters may be essential (especially, in cases of large SPEs and in emergency cases). The dynamical model of radiogenic leukemia risk assessment [1,2,3] can be employed (as a supplement to the estimations of cancer incidence and death REIC and REID) in the pre-mission design phase (e.g., for the optimization of the regimes of astronaut's additional shielding during large SPEs in trips to and from Mars), as well as in the phase of the real-time responses during Mars missions. This enables approaches to make the decisions on the operational application of appropriate countermeasures (including the adjustment of stay-times on the Mars surface and subsurface) to minimize the risks of occurrences of leukemia, particularly, in emergency cases. [1] O.A.Smirnova, Environmental Radiation Effects on Mammals: A Dynamical Modeling Approach (2nd ed.) Springer, Switzerland (2017); http://www.springer.com/978-3-319-45759-8 [2] O.A.Smirnova, F.A.Cucinotta, Life Sci. Sp. Res. 16, 76 (2018) [3] F.A.Cucinotta, O.A.Smirnova, Life Sci. Sp. Res. 19, 17 (2018) [4] D.M.Hassler et al., Science 343, 1244797 (2014) [5] Report NASA/SP-2009-566-ADD2 (2014)