TheGEANT4 general-purpose Monte Carlo simulation toolkit is able to simulate physical interaction processes of electrons, hydrogen and helium atoms with charge states (, ) and (, , ), respectively, in liquid water, the main component of biological systems, down to the electron volt regime and the submicrometer scale, providing GEANT4 users with the so-called “GEANT4-DNA” physics models suitable for microdosimetry simulation applications. The corresponding software has been recently re-engineered in order to provide GEANT4 users with a coherent and unique approach to the simulation of electromagnetic interactions within the GEANT4 toolkit framework (since GEANT4 version 9.3 beta). This work presents a quantitative comparison of these physics models with a collection of experimental data in water collected from the literature.Methods:
An evaluation of the closeness between the total and differential cross section models available in theGEANT4 toolkit for microdosimetry and experimental reference data is performed using a dedicated statistical toolkit that includes the Kolmogorov–Smirnov statistical test. The authors used experimental data acquired in water vapor as direct measurements in the liquid phase are not yet available in the literature. Comparisons with several recommendations are also presented.Results:
The authors have assessed the compatibility of experimental data withGEANT4microdosimetry models by means of quantitative methods. The results show that microdosimetric measurements in liquid water are necessary to assess quantitatively the validity of the software implementation for the liquid water phase. Nevertheless, a comparison with existing experimental data in water vapor provides a qualitative appreciation of the plausibility of the simulation models. The existing reference data themselves should undergo a critical interpretation and selection, as some of the series exhibit significant deviations from each other.Conclusions:
TheGEANT4-DNA physics models available in the GEANT4 toolkit have been compared in this article to available experimental data in the water vapor phase as well as to several published recommendations on the mass stopping power. These models represent a first step in the extension of the GEANT4 Monte Carlo toolkit to the simulation of biological effects of ionizing radiation.
The authors would like to thank all the authors whose models have been implemented in the GEANT4-DNA extension, especially M. Dingfelder and D. Emfietzoglou. In particular, the authors express their deep gratitude to M. Dingfelder for the helpful technical discussions that enabled the authors to verify the GEANT4-DNA software implementation and without whom this work could not have been achieved. The GEANT4-DNA project receives funding from the French Agence Nationale de la Recherche Contract No. ANR-09-BLAN-0135-01 and from the European Space Agency under Contract No. AO6041-22712/09/NL/AT. The authors are also grateful to John Sudmeier for proofreading this paper.
II. PHYSICAL INTERACTIONS FOR MICRODOSIMETRY AND THEIR GEANT4 IMPLEMENTATION
III. COMPARISON OF PHYSICS MODELS WITH EXPERIMENTAL DATA
III.A. GEANT4 simulations
III.B. Experimental reference data
III.C. Goodness-of-fit testing
IV. ELECTRON PROCESSES
IV.A. Elasticscattering total and differential cross sections
IV.D. Comparison of mass stopping power with recommendations
V. PROTON AND HYDROGEN PROCESSES
V.A. Ionization total and differential cross sections
V.B. Electron capture/loss total cross section
V.C. Total cross sections for excitation
V.D. Comparison of stopping power with ICRU and HRMP recommendations
VI. HELIUM PROCESSES
VI.A. Excitation and ionization total cross section
VI.B. Charge increase/decrease total cross section
VI.C. Comparison of stopping power with ICRU recommendations
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