Introduction: Most of the radionuclides that are used for diagnostic purposes emit Auger electrons and can thus cause damage to the DNA molecule on a nanometer scale. Therefore, the nanodosimetric calculation of these radioisotopes is necessary to achieve better understanding on their effects. Aim: The aim of this study was to calculate the mean number of DNA strand breaks (single-strand breaks and double-strand breaks) caused by direct and indirect effects for six widely used Auger electron-emitting diagnostic radioisotopes, including 123 I, 125 I, 99m Tc, 67 Ga, 201 Tl, 111 In and two therapeutic radioisotopes of 131 I(beta Auger CK emitter) and 211 At(alpha Auger CK emitter). Materials and Methods: Geant4-DNA simulation tool was used to evaluate the effects of Auger electrons, beta and alpha particles of these radioisotopes on DNA molecules. Two different DNA molecule geometric models were simulated and the results of these two models were compared with each other as well as with the results of previous studies. Results and Conclusion: The results showed that the geometric shape of the sugar-phosphate groups may have a significant effect on the number of single-strand breaks (SSBs) and double-strand breaks (DSBs) of the DNA molecule. Among the most widely used diagnostic radioisotopes, 201 Tl and 125 I, had the greatest impact on the number of SSBs and DSBs, respectively, while therapeutic radioisotope of 131 I almost had no effect, therapeutic radioisotope of 211 At had the moderate effect on the number of breaks in the DNA chain.
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