[Show abstract][Hide abstract] ABSTRACT: Monte Carlo simulations of S-values have been carried out with the Geant4-DNA extension of the Geant4 toolkit. The S-values have been simulated for monoenergetic electrons with energies ranging from 0.1 keV up to 20 keV, in liquid water spheres (for four radii, chosen between 10 nm and 1 µm), and for electrons emitted by five isotopes of iodine (131, 132, 133, 134 and 135), in liquid water spheres of varying radius (from 15 µm up to 250 µm). The results have been compared to those obtained from other Monte Carlo codes and from other published data. The use of the Kolmogorov-Smirnov test has allowed confirming the statistical compatibility of all simulation results.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/2014; 319:87-94. DOI:10.1016/j.nimb.2013.11.005 · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Modeling the radio-induced effects in biological medium still requires accurate physics models to describe the interactions induced by all the charged particles present in the irradiated medium in detail. These interactions include inelastic as well as elastic processes. To check the accuracy of the very low energy models recently implemented into the GEANT4 toolkit for modeling the electron slowing-down in liquid water, the simulation of electron dose point kernels remains the preferential test. In this context, we here report normalized radial dose profiles, for mono-energetic point sources, computed in liquid water by using the very low energy "GEANT4-DNA" physics processes available in the GEANT4 toolkit. In the present study, we report an extensive intra-comparison of profiles obtained by a large selection of existing and well-documented Monte-Carlo codes, namely, EGSnrc, PENELOPE, CPA100, FLUKA and MCNPX.
Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 02/2013; 83. DOI:10.1016/j.apradiso.2013.01.037 · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: On behalf of the Geant4 Standard and Low-Energy Electromagnetic Physics Working Groups. The authors are members of the Geant4-DNA collaboration. ABSTRACT Simulation of biological effects of ionizing radiation at the DNA scale requires not only the modeling of direct damages induced on DNA by the incident radiation and by secondary particles but also the modeling of indirect effects of radiolytic products resulting from water radiolysis. They can provoke single and double strand breaks by reacting with DNA. The Geant4 Monte Carlo toolkit is currently being extended for the simulation of biological damages of ionizing radiation at the DNA scale in the framework of the "Geant4-DNA" project. Physics models for the modeling of direct effects are already available in Geant4. In the present paper, an approach for the modeling of radiation chemistry in pure liquid water within Geant4 is presented. In particular, this modeling includes Brownian motion and chemical reactions between molecules following water radiolysis. First results on time-dependent radiochemical yields 1 from 1 picosecond up to 1 microsecond after irradiation are compared to published data and discussed. 1 For a given molecular species, the time-dependent radiochemical yield G is defined as the number of molecules produced for a total absorbed energy of 100 eV in the irradiated medium: , where N(t) is the number of molecules and E is the total energy deposit by the incident ionizing particle into the medium, expressed in eV.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a study of energy deposits induced by ionising particles in liquid water at the molecular scale. Particles track structures were generated using the Geant4-DNA processes of the Geant4 Monte-Carlo toolkit. These processes cover electrons (0.025 eV-1 MeV), protons (1 keV-100 MeV), hydrogen atoms (1 keV-100 MeV) and alpha particles (10 keV-40 MeV) including their different charge states. Electron ranges and lineal energies for protons were calculated in nanometric and micrometric volumes.
Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 01/2011; 69(1):220-6. DOI:10.1016/j.apradiso.2010.08.011 · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An overview of the electromagnetic (EM) physics of the Geant4 toolkit is presented. Two sets of EM models are available: the "Standard" initially focused on high energy physics (HEP) while the "Low-energy" was developed for medical, space and other applications. The "Standard" models provide a faster computation but are less accurate for keV energies, the "Low-energy" models are more CPU time consuming. A common interface to EM physics models has been developed allowing a natural combination of ultra-relativistic, relativistic and low-energy models for the same run providing both precision and CPU performance. Due to this migration additional capabilities become available. The new developments include relativistic models for bremsstrahlung and e+e- pair production, models of multiple and single scattering, hadron/ion ionization, microdosimetry for very low energies and also improvements in existing Geant4 models. In parallel, validation suites and benchmarks have been intensively developed.
[Show abstract][Hide abstract] ABSTRACT: In this note we discuss in general how to test the implementation code of statistical tests, and then we treat in detail the case of the Kolmogorov-Smirnov test. It will be shown that some “obvious ” expected properties, like the flatness distributions of p-values from repeating drawings from the same parent distribution, are not indeed reproduced even in absence of bugs in the code, due to either asymptotic approximations in the formulas used to compute the p-value, or to the discreteness of the distance distribution in the case of direct Monte Carlo evaluation of the p-value. This makes the code-testing more complicated. Some practical advice is presented anyhow. 1.
[Show abstract][Hide abstract] ABSTRACT: The GEANT4 general-purpose Monte Carlo simulation toolkit is able to simulate physical interaction processes of electrons, hydrogen and helium atoms with charge states (H0, H+) and (He0, He+, He2+), 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.
An evaluation of the closeness between the total and differential cross section models available in the GEANT4 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.
The authors have assessed the compatibility of experimental data with GEANT4 microdosimetry 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.
The GEANT4-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.
Medical Physics 09/2010; 37(9):4692-708. DOI:10.1118/1.3476457 · 3.01 Impact Factor