A new calculation on spectrum of direct DNA damage induced by low-energy electrons.

In this work, direct DNA damage induced by low-energy electrons (<5 keV) is simulated using Monte Carlo methods, and the resulting yield of various strand breaks and base damages in cellular environment is presented. The simulation is based on a new inelastic cross section for the production of electron track structure in liquid water, and on ionization cross sections of DNA bases to generate base radical. Especially, a systematic approach of simulating detailed base damage is suggested. This approach includes improvement of a volume model of DNA, generation of the DNA base sequence, conversion of ionization events in liquid water at hit site to the ionization interaction of electrons with DNA bases and development of an algorithm to convert a base radical to a damage. The results obtained in terms of strand breaks are compared with those of experiments and other theoretical calculations, and good agreement was obtained. The yield of detailed base damages and clustered DNA damages caused by the combination of various strand breaks and base damages is presented, and the corresponding distribution characteristics are analyzed. The influence of the relative content of base pairs A-T and G-C in a DNA segment on the yield of both strand breaks and base damages is also explored. The present work provides fundamental information on DNA damage and represents the first effort toward the goal of obtaining the spectrum of clustered DNA damage including detailed base damages, for the mechanistic interpretation and prediction of radiation effects.