Estimation of the radiation damage in CA1, CA2 and CA3 pyramidal and dentate granule cell neurons during proton and carbon-ion irradiation: A study with the Geant4 toolkit

Introduction Radiation damage to the central nervous system (CNS) has been a persistent problem for decades, owing to difficulties such as brain radiotherapy and astronaut radiation protection during space flight. Hippocampus is the most radiation-sensitive structure of the central nervous system. The present study aims to investigate damage induced by 12 C ions and proton radiation in pyramidal neurons of cornu ammonis regions and dentate granule neurons using Geant4 toolkit. Materials and Methods The Geant4/Geant4-DNA Monte Carlo toolkits were used to simulate the neuron shape and particle track structures. The computations were done for various energy proton beams and 12 C particles with different linear energy transfers from a few to hundreds of keV/µm. Damage to pyramidal and dentate granule neurons of hippocampus as well as length reduction of the dendrites were studied by the dose absorbed in dendrite and D TH (dendrites threshold dose). Also, in the present study, using Spearman’s correlation test, we examined the correlation between the morphological characteristics of neurons and the reduction in the length of their dendrites. Results According to the results obtained in this study, the apical dendrites of CA3 and the basal dendrites of CA1 were more vulnerable following proton irradiation and carbon ions with different energies under proton and carbon radiation. But, the pyramidal neurons of CA2 were more resistant to radiation than those of CA1and CA3 regions. Furthermore, the dentate granule neurons were more resistant to radiation than the pyramidal neurons. According to the results of Spearman’s correlation test, there was a statistical significance correlation (p-value< 0.05) between some of the morphological characteristics of neurons and the reduction in the length of their dendrites. Conclusion The results indicate that the neuron morphology is an important factor determining the accumulation of absorbed dose and length reduction of neurons. By evaluating the neurons with different morphology from the hippocampus, it was found that the dentate granule and pyramidal neurons had different vulnerabilities to radiation. The pyramidal neurons with less densely packed are more resistant to radiation.