Organ doses for monkey anatomy models with different postures exposed to external photons

Understanding how external radiation from nuclear accidents or radiological attacks affects internal human anatomy is essential to accurately assess health risks and develop effective treatments. we calculated a library of organ dose conversion coefficients for anatomical monkey models in a standing, crawling, and squatting postures for the first time by using Monte Carlo radiation transport methods combined with anatomical monkey models. We adopted previously published anatomical monkey models with three different postures: crawling, squatting, and standing. Radiation doses to a total of 39 organs and tissues were calculated using a general-purpose Monte Carlo radiation transport code, MCNP6.2, for the photon fields with 33 mono-energy bins ranging from 0.01 to 20 MeV in six different irradiation geometries: antero-posterior (AP), postero-anterior (PA), left lateral (LLAT), right lateral (RLAT), rotational (ROT), and isotropic (ISO). We found that the dose conversion coefficients derived from the standing posture may overestimate organ dose by up to 13-fold compared to the crawling position (e.g., large intestine in AP irradiation geometry). Irradiation geometry has the most substantial impact on organ doses in the crawling posture compared to squatting and standing postures. Average coefficients of variation over different organs were 51 % in crawling posture compared to 16 % and 17 % for standing and squatting postures, respectively. In the present research, we employed the Monte Carlo radiation transport techniques to develop a library of organ dose conversion coefficients for an anatomical monkey model considering various postures and six distinct irradiation geometries. We found that the existing dose conversion coefficients for the standing posture may substantially overestimate organ doses for monkeys in more natural postures. Our data should be useful for understanding the impact of radiation events to human anatomy by evaluating the impact on monkey's anatomy as a surrogate.