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S. Ftá_niková, R. Böhm, Monte Carlo Calculations of Energy Deposition in DNA for Auger Emitters, Radiation Protection Dosimetry, Volume 92, Issue 4, 1 December 2000, Pages 269–278, https://doi.org/10.1093/oxfordjournals.rpd.a033292
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Abstract
The Monte Carlo simulation of probability of radiation damage from incorporated Auger emitters to DNA and the mechanism of possible damage formation (single strand breaks (ssb) and double strand breaks (dsb) of DNA) in relation to track structures of the Auger electrons is reported. Three different models were used of the DNA macromolecule (CYLINDRICAL, DUPLEX and STRUCTURAL model) and the ETRACK code was applied to generate the position of energy deposition events in a water vapour medium for simulation of electron track. The evaluation of direct and indirect effects of monoenergetic electrons and also eight Auger emitters (99Tcm, 123I, 67Ga, 125I, 201Tl, 55Fe, 111In and 77Br) was performed. Electrons of initial energies from 50 eV to 250 eV have the highest probability of inducing ssb and dsb of DNA, because these electrons are able to produce clusters of inelastic interactions in a volume with diameter of a few nm. The indirect effect of radical species plays an important role in the DNA damage caused by Auger cascades. According to our calculations indirect effects of radiation produce more than 80% of DNA breaks. The radiotoxicity of 125I incorporated into DNA was studied. Calculation of the energy deposited during the 125I decay in small volumes showed that the quality of electron spectra used is a very important parameter. The value of energy deposited in a sphere with diameter of 10 nm can vary by a factor of 2-3.5 according to the spectra used. The primary difference in spectra is the inclusion (or exclusion) of very low energy 0-shell Coster-Kronig electrons. These differences do not have a major impact in terms of predicting DNA ssb and dsb caused by Auger emitters. For comparison of predicted radiotoxicity calculations were performed of average energy deposited in a sphere of 2 nm diameter and also the average number of DNA ssb and dsb for eight Auger emitters (125I, 99Tcm, 123I, 67Ga, 77Br, 201Tl, 111In, 55Fe). From our calculations, the value of average energy deposited in volume of diameter of 2 nm can serve as a useful first measure of an Auger emitter's radiotoxicity.
