In this study, the number of DNA damages including single, and double strand breaks (SSB and DSB) were calculated using the two geometric models (volume and atomic) of DNA strand. In this respect, the new advantage of Geant4.10.2 -p02 in simulating full Auger electron emission was used which considered the Auger Cascade and atomic deexcitation. The Geant4-DNA Low Energy Electromagnetic physics list was also used to track electrons in DNA. The calculations were performed for incorporation of 125I and 123I radionuclides in the form of radioiodinated iododeoxyuridine (IUdR). Then the results were recalculated using the two available Auger spectrums (ICRP and Pomplun). The effect of different geometrical models, and auger electron spectrums on DNA damage was investigated. The results showed that lower number of SSB and DSB was produced in atomic model compared with those for volume model. The same result was obtained when comparing the full Auger electron emission against available spectrums. This issue was raised because the average number of Auger electrons generated in the code was less than those from ICRP and Pomplun’s spectrum. Furthermore, it was found that the 125I and 123I radionuclides had approximately the same effect on DNA damage.

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