Calculation of complex DNA damage induced by ions

This paper is devoted to the analysis of the complex damage of DNA irradiated by ions. The assessment of complex damage is important because cells in which it occurs are less likely to survive because the DNA repair mechanisms may not be sufficiently effective. We study the flux of secondary electrons through the surface of nucleosomes and calculate the radial dose and the distribution of clustered damage around the ion's path. The calculated radial dose distribution is compared to simulations. The radial distribution of the complex damage is found to be different from that of the dose. A comparison with experiments may solve the question of what is more lethal for the cell, damage complexity or absorbed energy. We suggest a way to calculate the probability of cell death based on the complexity of the damage. This work is done within the framework of the phenomenon-based multiscale approach to radiation damage by ions.

Figure 1

Geometry of the problem. Secondary electrons radially diffuse from the ion's path and interact with a section of DNA molecule wrapped around a histone octamer.

Figure 2

Number of secondary electrons diffused through a two-convolution segment of DNA molecule on the surface of a nucleosome in the vicinity of the ion's path, plotted as a function of the distance $\rho$ of the nucleosome from the path. The calculation is done using the attenuation function given by Eq. (5).

Figure 3

Comparison of the calculated radial dose (line) [Eq. (9)] with that simulated in Ref. [23] (dots) for 25-MeV/nucleon carbon ions.

Figure 4

Calculated radial dose distribution for a LET of 0.9 keV/nm.

Figure 5

Radial distribution of clusters of two lesions (solid line) and clusters of three lesions (dashed line) for $\Gamma =0.1$.

Figure 6

Radial distribution of clusters of three and more lesions, deemed proportional to the probability of cell death. The solid curve corresponds to $\Gamma =0.1$ and the dashed curve corresponds to $\Gamma =0.3$.

Figure 7

Dependence of $1-P_d$, which is similar to the cell survival rate (dimensionless), on the local radial dose per ion with $\Gamma =0.3$.