Duration: 24 months
Estimating the biological effects of space radiation is challenging due to limited astronaut epidemiological data. For future Beyond-LEO (BLEO) missions, uncertainties in estimating stochastic and late deterministic effects are notable. The greatest uncertainty is in calculating the quality factor (Q) of space radiation for cancer induction. Currently, there is no consensus among space agencies regarding the calculation of Q, and experimental radiobiological data from space radiation is limited. Currently, only NASA employs an alternative method for calculating Q that does not depend on LET, but rather on the track structure parameter (z/β)2.
The study aims to develop a semi-analytic method for calculating Q for any space radiation environment based on the microdosimetric quantity lineal energy (y), which is fundamentally a better descriptor of radiation quality than LET and, most importantly, it is also directly measurable by TEPC detectors which are already used in LEO missions. The novelty of the proposed space-Q (SQ) model relies on the use of Geant4-DNA calculations of the effect of δ-rays on the microdosimetry of GCR ions, which may deposit as much as 80% of the primary ion energy. The SQ model will be parameterized as a function of dose (D) according to a microdosimetric-based linear-quadratic formulation which includes: (i) the microdosimetric dose-weighted lineal energy yD,k,d in a randomly distributed microscopic spherical target (diameter d) within the cell for each type (k) of ionizing radiation considered, and (ii) the radiosensitivity coefficients (α, β)m,k for each biological phenomenon (m) that will be derived from fitting to experimental data. The proposed SQ model is expected to be both functional and robust for use in risk models and for setting acceptable limits to astronauts in BLEO missions.
