Radiation Dosimetry of Inhaled Radioactive Aerosols: CFPD and MCNP Transport Simulations of Radionuclides in the Lung

Abstract

Despite extensive efforts in studying radioactive aerosols, including the transmission of radionuclides in different chemical matrices throughout the body, the internal organ-specific radiation dose due to inhaled radioactive aerosols has largely relied on experimental deposition data and simplified human phantoms. Computational fluid-particle dynamics (CFPD) has proven to be a reliable tool in characterizing aerosol transport in the upper airways, while Monte Carlo based radiation codes allow accurate simulation of radiation transport. The objective of this study is to numerically assess the radiation dosimetry due to particles decaying in the respiratory tract from environmental radioactive exposures by coupling CFPD with Monte Carlo N-Particle code, version 6 (MCNP6). A physiologically realistic mouth-lung model extending to the bifurcation generation G9 was used to simulate airflow and particle transport within the respiratory tract. Polydisperse aerosols with different distributions were considered, and deposition distribution of the inhaled aerosols on the internal airway walls was quantified. The deposition mapping of radioactive aerosols was then registered to the respiratory tract of an image-based whole-body adult male model (VIP-Man) to simulate radiation transport and energy deposition. computer codes were developed for geometry visualization, spatial normalization, and source card definition in MCNP6. Spatial distributions of internal radiation dosimetry were compared for different radionuclides (131 i, 134,137 cs, 90 Sr-90 Y, 103 Ru and 239,240 Pu) in terms of the radiation fluence, energy deposition density, and dose per decay. Radioactive aerosols arise from various sources such as nuclear accidents, natural decay processes, and the decommissioning of nuclear reactors 1-3. Highly radioactive micro-particles were released to the surrounding environment in the Chernobyl and Fukushima Daiichi accidents 1,4. The aerosol particles released from accidents and natural decay processes may remain suspended in the air for extended periods, be incorporated into soil particles that can reenter the air, or be inhaled by humans or animals. When aerosol particles are inhaled, a fraction of the inhaled particles deposit in the respiratory tract, while the rest is exhaled out 5-9. The deposition fraction is dependent on many parameters such as the geometry of the respiratory airways, the particle size of the inhaled aerosol, and the breathing condition 10,11. Inhaled radioactive aerosols can expose internal organs to radiation for extended periods and may induce a spectrum of functional and morphological changes, such as genetic mutations and carcinogenesis 12,13. Their severity can be related to the absorbed radiation dose in the different specific tissues, which is further related to the number of radioactive particles inhaled, how long they stay, and the type of radiation they emit. Unlike fat and muscles being the main internal defense to external exposures, there is nothing to protect cells and tissues of sus...

Numerical investigation of aerosol transport in a classroom with relevance to COVID-19

“…Computational fluid dynamics has been used in many studies to investigate aerosol transport in outdoor conditions, 14 indoor conditions such as hospitals, 6,15 and even inside the human airway system with good agreement with the experimental data. 16,17 During the COVID-19 pandemic, significant efforts have been made to develop computational fluid dynamics models of the human sneeze, 18 investigate mask mechanics, 19 and study aerosol transport and air flow in different environments and conditions such as aircrafts, 20 vehicular cabins, 1 urinals and toilets, 21,22 public spaces, 23 and indoor spaces. 24,25 Despite these efforts, to the authors’ knowledge, no studies have investigated aerosol transport in a classroom environment although classroom sizes, the air conditioning layout, and aerosol source distribution are characteristically different than hospital care units and other indoor spaces discussed in the literature.…”

Liquid Film Translocation Significantly Enhances Nasal Spray Delivery to Olfactory Region: A Numerical Simulation Study

“…The evaporation/hygroscopic effect on droplet dynamics was neglected considering that the temperature is constant and the relative humidity is close to saturation [ 55 ]. Additionally, droplet size distribution [ 56 ], electrostatic charge [ 57 , 58 , 59 , 60 ], and droplet collisions [ 61 ] were neglected for simplicity purposes in modeling and simulations. Practically, neglecting these minor factors allowed the isolation of the dominant factors (wall film migration) to be examined in a controlled manner.…”

Health Effects of Particulate Uranium Exposure

“…Aerosols are flowable, a complex two-phase flow of material that not only deposits in specific organs or tissues, but also diffuses and transfers from one organ or tissue to surrounding organs or tissues [ 43 ]. When aerosol particles are inhaled, a portion of the inhaled particles are deposited in the respiratory tract and the rest is exhaled [ 5 ].…”

“…It is worth noting that even if particles are deposited in the lungs, radioactive exposure can affect the entire organism because peripheral doses can be delivered to nearby organs. The biological pathway from the respiratory tract to the rest of the body depends on the dissolution of particles in the alveoli and their absorption by the blood [ 43 ].…”