Absorbed dose calculation for a realistic CT-derived mouse phantom irradiated with a standard Cs-137 cell irradiator using a Monte Carlo method

Amir Entezam; Andrew Fielding; David Bradley; Davide Fontanarosa

doi:10.1371/journal.pone.0280765

Absorbed dose calculation for a realistic CT-derived mouse phantom irradiated with a standard Cs-137 cell irradiator using a Monte Carlo method

PLoS One. 2023 Feb 2;18(2):e0280765. doi: 10.1371/journal.pone.0280765. eCollection 2023.

Authors

Amir Entezam^{1

2

3}, Andrew Fielding^{2

4}, David Bradley^{5

6}, Davide Fontanarosa^{1

2}

Affiliations

¹ School of Clinical Sciences, Queensland University of Technology, Brisbane, QLD, Australia.
² Centre for Biomedical Technologies, Queensland University of Technology, Brisbane, QLD, Australia.
³ Translational Research Institute, The University of Queensland, Brisbane, QLD, Australia.
⁴ School of Chemistry and Physics, Faculty of Science, Queensland University of Technology, Brisbane, QLD, Australia.
⁵ Centre for Applied Physics and Radiation Technologies, Sunway University, PJ, Malaysia.
⁶ Department of Physics, University of Surrey, Guildford, United Kingdom.

Abstract

Computed tomography (CT) derived Monte Carlo (MC) phantoms allow dose determination within small animal models that is not feasible with in-vivo dosimetry. The aim of this study was to develop a CT-derived MC phantom generated from a mouse with a xenograft tumour that could then be used to calculate both the dose heterogeneity in the tumour volume and out of field scattered dose for pre-clinical small animal irradiation experiments. A BEAMnrc Monte-Carlo model has been built of our irradiation system that comprises a lead collimator with a 1 cm diameter aperture fitted to a Cs-137 gamma irradiator. The MC model of the irradiation system was validated by comparing the calculated dose results with dosimetric film measurement in a polymethyl methacrylate (PMMA) phantom using a 1D gamma-index analysis. Dose distributions in the MC mouse phantom were calculated and visualized on the CT-image data. Dose volume histograms (DVHs) were generated for the tumour and organs at risk (OARs). The effect of the xenographic tumour volume on the scattered out of field dose was also investigated. The defined gamma index analysis criteria were met, indicating that our MC simulation is a valid model for MC mouse phantom dose calculations. MC dose calculations showed a maximum out of field dose to the mouse of 7% of Dmax. Absorbed dose to the tumour varies in the range 60%-100% of Dmax. DVH analysis demonstrated that tumour received an inhomogeneous dose of 12 Gy-20 Gy (for 20 Gy prescribed dose) while out of field doses to all OARs were minimized (1.29 Gy-1.38 Gy). Variation of the xenographic tumour volume exhibited no significant effect on the out of field scattered dose to OARs. The CT derived MC mouse model presented here is a useful tool for tumour dose verifications as well as investigating the doses to normal tissue (in out of field) for preclinical radiobiological research.

Copyright: © 2023 Entezam et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Cesium Radioisotopes*
Humans
Mice
Monte Carlo Method
Neoplasms*
Phantoms, Imaging
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Tomography, X-Ray Computed

Substances

Cesium-137
Cesium Radioisotopes

Grants and funding

This work was supported by Queensland University of Technology grant (Institute of Health and Biomedical Innovation (IHBI) John Williams Cancer Research Scholar). he funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.