The γH2AX DSB marker may not be a suitable biodosimeter to measure the biological MRT valley dose

Abstract

Purpose

γH2AX biodosimetry has been proposed as an alternative dosimetry method for microbeam radiation therapy (MRT) because conventional dosimeters, such as ionization chambers, lack the spatial resolution required to accurately measure the MRT valley dose. Here we investigated whether γH2AX biodosimetry should be used to measure the biological valley dose of MRT-irradiated mammalian cells.

Materials and methods

We irradiated human skin fibroblasts and mouse skin flaps with synchrotron MRT and broad beam (BB) radiation. BB doses of 1–5 Gy were used to generate a calibration curve in order to estimate the biological MRT valley dose using the γH2AX assay.

Results

Our key finding was that MRT induced a non-linear dose response compared to BB, where doses 2–3 times greater showed the same level of DNA DSB damage in the valley in cell and tissue studies. This indicates that γH2AX may not be an appropriate biodosimeter to estimate the biological valley doses of MRT-irradiated samples. We also established foci yields of 5.9 ± $0.04$ and 27.4 ± $2.5\mathrm{ }$ foci/cell/Gy in mouse skin tissue and human fibroblasts respectively, induced by BB. Using Monte Carlo simulations, a linear dose response was seen in cell and tissue studies and produced predicted peak-to-valley dose ratios (PVDRs) of ∼30 and ∼107 for human fibroblasts and mouse skin tissue respectively.

Conclusions

Our report highlights novel MRT radiobiology, attempts to explain why γH2AX may not be an appropriate biodosimeter and suggests further studies aimed at revealing the biological and cellular communication mechanisms that drive the normal tissue sparing effect, which is characteristic of MRT.

Keywords:

• Biodosimetry
• γH2AX
• DNA damage
• synchrotron radiation
• microbeam radiation therapy
• dose response curve

Acknowledgements

We acknowledge beam time from ANSTO/The Australian Synchrotron on the Imaging & Medical Beamline in 2016 and 2017. We also thank Olga Martin and Pavel Lobachevsky of Peter MacCallum Cancer Centre, for critical reading of the manuscript, and Andrew Stevenson and Christopher Hall for technical assistance and support with use of the Imaging and Medical Beamline at the Australian Synchrotron. The authors also thank Cameron Patrick of the Melbourne Statistical Consulting Platform at the University of Melbourne, for valuable advice on statistical analysis of the data. We thank Dr Duncan Butler from the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) for his assistance with the uncertainty calculations.

Disclosure statement

The authors declare no potential conflict of interest.

Data availability statement

The macros generated in this study can be accessed via FigShare at DOI: https://doi.org/10.6084/m9.figshare.12333113.v1

Additional information

Funding

This study was supported by the Australian National Health and Medical Research Council (NHMRC) grant no. APP1061772. J.A.Ventura was supported by the Felix Meyer Scholarship in Obstetrics and Gynaecology at the Faculty of Medicine, Dentistry and Health Sciences, the University of Melbourne.

Notes on contributors

Jessica A. Ventura

Jessica A. Ventura, Ph.D. candidate at the Department of Obstetrics and Gynaecology, Royal Women’s Hospital, University of Melbourne, Parkville, Australia.

Jacqueline F. Donoghue

Jacqueline F. Donoghue, Ph.D., is a Senior Research Fellow at the Department of Obstetrics and Gynaecology, Royal Women’s Hospital, University of Melbourne, Parkville, Australia.

Cameron J. Nowell

Cameron J. Nowell, is the Head of the Imaging, FACS and Analysis Core at the Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Australia.

Leonie M. Cann

Leonie M. Cann, is a Research Assistant at the Department of Obstetrics and Gynaecology, Royal Women’s Hospital, University of Melbourne, Parkville, Australia.

Liam R. J. Day

Liam R. J. Day, Ph.D. candidate at the School of Science, RMIT University, Melbourne, Australia.

Lloyd M. L. Smyth

Lloyd M. L. Smyth, Ph.D. candidate at the Department of Obstetrics and Gynaecology, Royal Women’s Hospital, University of Melbourne, Parkville, Australia.

Helen B. Forrester

Helen B. Forrester, Ph.D., is a Senior Research Fellow at the Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Monash University, Clayton, Australia, and the Department of Molecular and Translational Sciences, Monash University, Clayton, Australia.

Peter A. W. Rogers

Peter A. W. Rogers, Ph.D., is a Professor of Women’s Health Research at the Department of Obstetrics and Gynaecology, Royal Women’s Hospital, University of Melbourne, Parkville, Australia.

Jeffrey C. Crosbie

Jeffrey C. Crosbie, Ph.D., is an Associate Professor of Medical Physics at the School of Science, RMIT University, Melbourne, Australia.