Influence of excitation and geometrical parameters on the VUV radiation of a pure xenon dielectric barrier discharge

International audienc

Polymérisation radio-induite (calcul de dose et modélisation dans le cas d'irradiations prolongées de sources non-scellées)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Radiothérapie guidée par l'image (maîtrise des éléments matériels)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Sub-keV corrections to binary encounter cross section models for electron ionization of liquid water with application to the Geant4-DNA Monte Carlo code

International audienceIntroductionThe electron ionization cross section of water is one of the most important input in Monte Carlo studies of cellular radiobiological effects. Analytical cross section models of the binary-encounter type have the potential of reducing simulation time and facilitate application to a variety of biological materials (other than water). The Binary-Encounter-Bethe (BEB) and Binary-Encounter-Dipole (BED) models of NIST are perhaps the most popular of such models giving reliable results for atoms and molecules in the gas-phase over a wide energy range. However, the use of such models to sub-keV electron energies in liquid water raises concerns due to the neglect of condensed phase effects that leads to a significant overestimation when compared to medium-specific dielectric models.PurposeTo modify the BEB and BED models towards better agreement with the recommended low-energy dielectric model of Geant4-DNA (Option 4). To implement the new modifications to the existing BEB model of the Option 6 physics constructor of Geant4-DNA and re-evaluate fundamental transport quantities for sub-keV electrons.MethodsIn analogy to a Yukawa potential a simple, yet physically-motivated, modification of the Burgess correction term is proposed to account for the reduction of the Coulomb interaction due to the polarizability of the target. The magnitude of the correction is guided by the dielectric-based ionization cross section implemented in Option 4.ResultsDifferential, total and stopping ionization cross sections for low-energy electrons in liquid water are presented. When combined with the Vriens correction (which is not included in Option 6), the proposed modification to the BEB and BED models brings the ionization and stopping cross sections in much better agreement against those used in the Option 4 dielectric model of Geant4-DNA, with up to 30% and 10% deviation, respectively. Implementation of the new correction to the Option 6 constructor of Geant4-DNA and re-evaluation of fundamental transport quantities, such as electron penetration ranges and dose-point-kernels, reduced the discrepancies from Option 4 at sub-keV energies from 20 to 100% (or more) to well below 10% in most cases.ConclusionsA simple modification to the BEB and BED analytic models was found to improve their performance for sub-keV electrons in liquid water medium. Implementation of the new modification to the Option 6 constructor of Geant4-DNA significantly improved the agreement with the recommended low-energy Option 4 constructor for a variety of fundamental quantities related to electron transport

Low-energy electron dose-point kernel simulations using new physics models implemented in Geant4-DNA

International audienceWhen low-energy electrons, such as Auger electrons, interact with liquid water, they induce highly localized ionizing energy depositions over ranges comparable to cell diameters. Monte Carlo track structure (MCTS) codes are suitable tools for performing dosimetry at this level. One of the main MCTS codes, Geant4-DNA, is equipped with only two sets of cross section models for low-energy electron interactions in liquid water (“option 2” and its improved version, “option 4”). To provide Geant4-DNA users with new alternative physics models, a set of cross sections, extracted from CPA100 MCTS code, have been added to Geant4-DNA. This new version is hereafter referred to as “Geant4-DNA-CPA100”.In this study, “Geant4-DNA-CPA100” was used to calculate low-energy electron dose-point kernels (DPKs) between 1 keV and 200 keV. Such kernels represent the radial energy deposited by an isotropic point source, a parameter that is useful for dosimetry calculations in nuclear medicine. In order to assess the influence of different physics models on DPK calculations, DPKs were calculated using the existing Geant4-DNA models (“option 2” and “option 4”), newly integrated CPA100 models, and the PENELOPE Monte Carlo code used in step-by-step mode for monoenergetic electrons. Additionally, a comparison was performed of two sets of DPKs that were simulated with “Geant4-DNA-CPA100” – the first set using Geant4′s default settings, and the second using CPA100′s original code default settings.A maximum difference of 9.4% was found between the Geant4-DNA-CPA100 and PENELOPE DPKs. Between the two Geant4-DNA existing models, slight differences, between 1 keV and 10 keV were observed. It was highlighted that the DPKs simulated with the two Geant4-DNA’s existing models were always broader than those generated with “Geant4-DNA-CPA100”. The discrepancies observed between the DPKs generated using Geant4-DNA’s existing models and “Geant4-DNA-CPA100” were caused solely by their different cross sections. The different scoring and interpolation methods used in CPA100 and Geant4 to calculate DPKs showed differences close to 3.0% near the source

Opening Address

蛋白质翻译后修饰系统几乎参与了细胞所有的正常生命活动过程，并发挥着重要的调控作用。目前，基于生物质谱技术进行蛋白质翻译后修饰的规模化分析鉴定，已经成为蛋白质组学研究的核心内容之一。近年来的研究表明，蓝藻细胞中存在着复杂的蛋白质翻译后修饰系统，如磷酸化，乙酰化，甲基化，糖基化，氧化等，这些翻译后修饰在蓝藻细胞的代谢过程中可能发挥着重要的调控作用。本文主要针对蓝藻细胞中蛋白质翻译后修饰的发现与鉴定，以及翻译后修饰潜在的生物学功能展开简要综述

Monte Carlo simulations of electron interactions with the DNA molecule: A complete set of physics models for Geant4-DNA simulation toolkit

International audienceIn this study we are introducing an update of the Geant4-DNA physics constructor “option 6” including electron interactions with all constituents of the DNA molecule in addition to those already publicly available for liquid water. The new implementation is based on the interaction cross sections of electrons with the four DNA nucleobases, deoxyribose and phosphoric acid for elastic scattering, electronic excitation and ionisation in the 11 eV – 1 MeV energy range. An additional sampling method to estimate the transferred secondary electron energy produced by ionisation is also introduced and can be optionally activated instead of the classical interpolation method based on the differential cross section tables, thus eliminating the need to upload large data files. The implementation in Geant4-DNA was verified by calculating range and electronic stopping power in the various materials. Good agreement is observed with the data available in the literature, and calculations with the interpolation method and the sampling method showed less than 4% difference. No differences were observed in terms of computational cost

Complex cell geometry and sources distribution model for Monte Carlo single cell dosimetry with iodine 125 radioimmunotherapy

In cellular dosimetry, common assumptions consider concentric spheres for nucleus and cell and uniform radionuclides distribution. These approximations do not reflect reality, specially in the situation of radioimmunotherapy with Auger emitters, where very short-ranged electrons induce hyper localised energy deposition. A realistic cellular dosimetric model was generated to give account of the real geometry and activity distribution, for non-internalizing and internalizing antibodies (mAbs) labelled with Auger emitter I-125. The impact of geometry was studied by comparing the real geometry obtained from confocal microscopy for both cell and nucleus with volume equivalent concentric spheres. Non-uniform and uniform source distributions were considered for each mAbs distribution. Comparisons in terms of mean deposited energy per decay, energy deposition spectra and energy-volume histograms were calculated using Geant4. We conclude that realistic models are needed, especially when energy deposition is highly non-homogeneous due to source distribution