Calculation of DNA strand breaks due to direct and indirect effects of Auger electrons from incorporated 123I and 125I radionuclides using the Geant4 computer code

Abstract

Purpose: In this work the number of DNA single-strand breaks (SSB) and double-strand breaks (DSB) due to direct and indirect effects of Auger electrons from incorporated 123I and 125I have been calculated by using the Geant4-DNA toolkit. We have performed and compared the calculations for several cases: 125I versus 123I, source positions and direct versus indirect breaks to study the capability of the Geant4-DNA in calculations of DNA damage yields.Materials and methods: Two different simple geometries of a 41 base pair of B-DNA have been simulated. The location of 123I has been considered to be in 123IdUrd and three different locations for 125I.Results: The results showed that the simpler geometry is sufficient for direct break calculations while indirect damage yield is more sensitive to the helical shape of DNA. For 123I Auger electrons, the average number of DSB due to the direct hits is almost twice the DSB due to the indirect hits. Furthermore, a comparison between the average number of SSB or DSB caused by Auger electrons of 125I and 123I in 125IdUrd and 123IdUrd shows that 125I is 1.5 times more effective than 123I per decay.Conclusions: The results are in reasonable agreement with previous experimental and theoretical results which shows the applicability of the Geant-DNA toolkit in nanodosimetry calculations which benefits from the open-source accessibility with the advantage that the DNA models used in this work enable us to save the computational time. Also, the results showed that the simpler geometry is suitable for direct break calculations, while for the indirect damage yield, the more precise model is preferred.