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.

Keywords::

• DNA
• strand breaks
• direct and indirect hits
• Auger electrons
• Geant4-DNA
• Monte Carlo method