A Geant4 simulation for three-dimensional proton imaging of microscopic samples

Abstract

In these experiments, the samples are dehydrated for under vacuum analysis. In situ quantification of nanoparticles has been carried out at CENBG in the frame of nanotoxicology studies, on cells and small organisms used as biological models, especially on Caenorhabditis elegans (C. elegans) nematodes. Tomography experiments reveal the distribution of mass density and chemical content (in g.cm-3) within the analyzed volume. These density values are obtained using an inversion algorithm. To investigate the effect of this data reduction process, we defined different numerical phantoms, including a (dehydrated) C. elegans phantom whose geometry and density were derived from experimental data. A Monte Carlo simulation based on the Geant4 toolkit was developed. Using different simulation and reconstruction conditions, we compared the resulting tomographic images to the initial numerical reference phantom. A study of the relative error between the reconstructed and the reference images lead to the result that 20 protons per shot can be considered as an optimal number for 3D STIM imaging. Preliminary results for PIXE tomography are also presented, showing the interest of such numerical phantoms to produce reference data for future studies on X-ray signal attenuation in thick samples.

A Geant4 simulation of X-ray emission for three-dimensional proton imaging of microscopic samples

“…A specific sample preparation protocol was designed, with cryofixation followed by freeze-drying, in order to preserve the sample structure and elemental composition at the cellular level [19,20]. A numerical phantom of the upper part of a C. elegans worm was designed, whose geometry, density and composition were derived from experimental data measured from real C. elegans samples grown in the presence of TiO2 nanoparticles in their culture medium, and detailed in a previous publication [15]. As explained in that publication, the original (biological) concentrations from this phantom would be too low to allow Geant4 simulations to be performed in a reasonable time.…”

“…The simulation of computed tomography with a proton beam of a few MeV has been designed using the Geant4 toolkit, and described in detail in a previous publication [15]. New developments were carried out to improve the ergonomics and speed of the code, especially for execution in multithreading mode and for the management of output data files.…”

“…A possible way to evaluate the precision of the reconstruction process is to compare the results obtained from the same experimental data sets, using different data reduction and tomographic reconstruction methods compared to one another [10,11]. In order to quantify in a more direct way the accuracy of the reconstruction, we proposed to use the Geant4 toolkit (http://geant4.org) [12][13][14] as a benchmark and we defined numerical phantoms for this purpose [15]. This first study demonstrated a good agreement between the calculated PIXE densities and the reference data for thin objects (for example a 5 µm cubic phantom).…”

Implementation of the EPICS2017 database for photons in Geant4

“…Livermore physics models constitute an important component of the sub-package and are based on three evaluated data libraries of the Lawrence Livermore National Laboratory (LLNL) for elements with atomic number Z = 1-100: i) EPDL97 (Evaluated Photons Data Library) [7], ii) EEDL (Evaluated Electrons Data Library) [8], iii) EADL (Evaluated Atomic Data Library) [9]. These models have been utilized in space radiation [10], archeology [11] and medical physics applications, particularly in radiotherapy [12,13], micro-and nanodosimetry [14,15], imaging [16,17] and spectrometry [18,19]. Especially for medical physics, it is now possible to model the interaction of particles with living matter down to the molecular level (DNA), opening the way to a finer understanding of the mechanisms occurring during and following irradiation [20].…”

Advances in Geant4 applications in medicine

“…On a similar topic, Solovev et al presented Geant4 simulations allowing to set up radiobiological experiments with carbon ions at the U-70 synchrotron in Protvino, Russia. Michelet et al [17] presented Geant4 simulations for 3D proton imaging of microscopic samples, and Sarno et al described cone-beam breast CT also using Geant4. Beaudoux et al [18] compared Geant4 electromagnetic physics lists for the simulation of phase-contrast mammography (in the context of the "XPulse" project) and finally Sosnovec described the possibilities to treat cancer by photodynamic therapy and related improvements.…”