Response to the Commentary from Bevelacqua et al.

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This response clarifies certain misconceptions published in the commentary by Bevelacqua et al. (2019). We are pleased that our article entitled “New concerns for neurocognitive function during deep space exposures to chronic, low dose rate, neutron radiation” (Acharya et al., 2019) has stimulated interesting discussions and different perspectives on what may or may not be relevant to estimating the risks of CNS dysfunction following exposure to the space radiation environment. Here we provide our response to the commentary from Bevelacqua et al. (2019). Bevelacqua et al. (2019) stated that there were a few major shortcomings with our approach, and we would like to clarify our stance regarding those statements. The first and perhaps most disconcerting statement was their assertion that we have ignored “…that in a realistic space environment, cells will be exposed to multiple low LET (linear energy transfer) protons before being traversed by intermediate and high-LET HZE (high charge and energy) particles.” The authors of Acharya et al. (2019) have conducted research at heavy ion particle accelerators around the world for more than a decade, and the implication that we might be unaware of the complexities of the radiation fields in space is misguided (Parihar et al., 2015, 2016, 2018; Lee et al., 2017). During long-term missions into deep space, astronauts will be exposed to a complex radiation field that includes high LET components from high energy, heavy ions (HZE particles) at low dose rates of ∼0.5 mGy/d for long durations. About 20% of the dose is delivered with LET >10 keV/μm. Particle accelerators are capable of simulating components of the galactic cosmic radiation (GCR) spectrum. The main impediment to performing accelerator-based experiments, which are designed to simulate exposures to …