Comparing the DNA-damage RBE of intraoperative and conventional electron beams using a hybrid simulation approach

Abstract

Purpose

Employing electron beam for radiotherapy purposes now has been established as one of the standard cancer treatment modalities. Both dedicated intraoperative and conventional electron beams can be employed in patient irradiation. Due to the differences between accelerating structure and electron beam delivery of dedicated intraoperative radiotherapy (IORT) machines and conventional ones, the initial energy spectra of the produced electron beam by these machines may be different. Accordingly, this study aims to evaluate whether these spectral differences can affect the relevant relative biological effectiveness (RBE) values of intraoperative and conventional electron beams.

Materials and methods

A hybrid Monte Carlo simulation approach was considered. At first, the head LIAC12 machine (as an IORT accelerator) and Varian 2100C/D (as a conventional accelerator) were simulated by MCNPX code and electron energy spectra at different depths and off-axis distances were scored for two nominal electron energies of 6 and 12 MeV at the field sizes of 6 and 10 cm. Then, the calculated spectra were imported to MCDS code to estimate the induced DNA-damage RBE values. Finally, the obtained RBE values for intraoperative and conventional electron beams were compared together.

Results

The results showed that the RBE values of the intraoperative electron beam are superior to those obtained for conventional electron beam at the same energy/field size combination. Variations of the depth can regularly affect the RBE value for both conventional and intraoperative electron beams, while no ordered variation trend was observed for RBE with changing the off-axis distance. Variations of electron energy and field size can also influence the RBE value for both types of studied electron beams.

Conclusions

From the results, it can be concluded the structural differences between the dedicated IORT and conventional Linacs can lead to distinct initial electron energy spectra for intraoperative and conventional electron beams. These physical differences can finally lead to different RBE values for intraoperative and conventional electron beams at the same energy and field size.

Keywords:

• Radiotherapy
• intraoperative electron beam
• conventional electron beam
• RBE
• Monte Carlo simulation

Disclosure statement

The authors report there are no competing interests to declare.

Additional information

Funding

None declared.

Notes on contributors

Hamid Reza Baghani

Hamid Reza Baghani, Ph.D., is an Associate Professor and Medical Physicist at the Department of Physics, Hakim Sabzevari University, Sabzevar, Iran.

Ali Shiri

Ali Shiri, M.Sc., graduated in Medical Physics at the Department of Medical Physics, Mashhad University of Medical Sciences, Mashhad, Iran.

Hamid Gholamhosseinian

Hamid Gholamhosseinian, Ph.D., is an Assistant Professor and Medical Physicist at the Department of Medical Physics, Mashhad University of Medical Sciences, Mashhad, Iran.