Clustered DNA Damage Formation in Human Cells after Exposure to Low- and Intermediate-Energy Accelerated Heavy Ions

Based on the differentiated analysis of individual radiation-induced foci in three-dimensional images reconstructing the entire volume of the cell nucleus, a detailed analysis of the structure of complex DNA damage clusters in accelerated ion tracks is carried out, and the differences in damage cluster morphology are investigated. It has been found that after exposure to accelerated heavy ions of low and intermediate energies, unlike γ-rays, complex clusters are formed, including up to six and more individual foci. The obtained results showed that the structure of clustered DNA damage depend on particle LET. The kinetics of the elimination of radiation-induced foci in cells after heavy ion exposure is shown to be slower than after γ‑irradiation. It is concluded that the delay in kinetics is associated with the nature of the microdistribution of heavy charged particles' energy in genetic structures and the formation of complex DNA double-strand breaks (DSBs), which are difficult to repair. A study of the kinetics of radiation-induced foci formation and elimination after exposure to accelerated boron, nitrogen, and neon ions with different physical characteristics has shown that with a decrease in the particles’ energy and an increase in their LET, the effectiveness of DNA DSB repair decreases. It is shown that the structure of radiation-induced foci caused by accelerated ions with different physical characteristics is also different. Neon ions with a high density of δ-electrons in the track induce larger and more complex foci clusters.