Evaluation of DNA damage induced by Auger electrons from ¹³⁷Cs

Abstract

Purpose: To understand the biological effect of external and internal exposure from ¹³⁷Cs, DNA damage spectrum induced by directly emitted electrons (γ-rays, internal conversion electrons, Auger electrons) from ¹³⁷Cs was compared with that induced by ¹³⁷Cs γ-rays. Methods: Monte Carlo track simulation method was used to calculate the microscopic energy deposition pattern in liquid water. Simulation was performed for the two simple target systems in microscale. Radiation sources were placed inside for one system and outside for another system. To simulate the energy deposition by directly emitted electrons from ¹³⁷Cs placed inside the system, the multiple ejections of electrons after internal conversion were considered. In the target systems, induction process of DNA damage was modeled and simulated for both direct energy deposition and the water radical reaction on the DNA. The yield and spatial distribution of simple and complex DNA damage including strand breaks and base lesions were calculated for irradiation by electrons and γ-rays from ¹³⁷Cs. Results: The simulation showed that the significant difference in DNA damage spectrum was not caused by directly ejected electrons and γ-rays from ¹³⁷Cs. Conclusions: The result supports the existing perception that the biological effects by internal and external exposure by ¹³⁷Cs are equivalent.

Keywords:

• ¹³⁷Cs
• internal exposure
• external exposure
• Auger electrons
• DNA damage
• Monte Carlo simulation

Acknowledgements

This work was partially supported by a grant from the Ministry of Education, Culture, Sport, Science and Technology under contract 15H02823. The authors thank Dr Kimiaki Saito and Dr Tatsuhiko Sato (Japan Atomic Energy Agency) and Professor Nobuyoshi Akimitsu (University of Tokyo) for their helpful discussion, and Mr Tadashi Imaki and Mr Kenji Masuko (Research Organization for Information Science and Technology) for their assistance in the visualization technique.

Disclosure statement

The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.