In Silico Nanodosimetry: New Insights into Nontargeted Biological Responses to Radiation

The long-held view that radiation-induced biological damage must be initiated in the cell nucleus, either on or near DNA itself, is being confronted by mounting evidence to suggest otherwise. While the efficacy of cell death may be determined by radiation damage to nuclear DNA, a plethora of less deterministic biological responses has been observed when DNA is not targeted. These so-called nontargeted responses cannot be understood in the framework of DNA-centric radiobiological models; what is needed are new physically motivated models that address the damage-sensing signalling pathways triggered by the production of reactive free radicals. To this end, we have conducted a series of in silico experiments aimed at elucidating the underlying physical processes responsible for nontargeted biological responses to radiation. Our simulation studies implement new results on very low-energy electromagnetic interactions in liquid water (applicable down to nanoscales) and we also consider a realistic simulation of extranuclear microbeam irradiation of a cell. Our results support the idea that organelles with important functional roles, such as mitochondria and lysosomes, as well as membranes, are viable targets for ionizations and excitations, and their chemical composition and density are critical to determining the free radical yield and ensuing biological responses

Mesure de la fonction de structure polarisée g1n du neutron par l'expérience E154 au SLAC

This thesis presents the precision measurement of the neutron polarized structure g1n performed by the E154 collaboration at the Stanford Linear Accelerator Center, USA, in autumn 1995, using a 48.3 GeV polarized electron beam scattered off a polarized Helium 3 target. The scattered electrons were detected using two spectrometer arms, covering the deep inelastic scattering range : 0.014 < x < 0.7 and 1 GeV2 < Q2 < 17 GeV2 at an average value of Q2 = 5 GeV2. Two electromagnetic calorimeters have been designed by the LPC in Clermont-Ferrand and the SphN-CEA in Saclay to measure the scattered electron energy and to reject the contaminating hadron background, using a cellular automaton and a neural network, widely described in this thesis. The analysis performed in Clermont-Fd and presented in this document led us to the integral on the measured region : integral (g1n(x)dx, xmin=0.0135, xmax=0.7) = -0.03 +- 0.003 STAT +- 0.004 SYST +- 0.001 EVOL at Q2 = 5 GeV2 where our data have been evolved to Q2 = 5 GeV2 using the next-to-leading order DGLAP evolution equations and a world parametrization of the polarized parton distributions. The Ellis and Jaffe sum rule is clearly violated. Using different low x extrapolations, our integral is compatible with the Bjorken sum rule. The quark contribution to the nucleon spin is DeltaSigma = 29 ± 6 % in the MS bar scheme and DeltaSigma = 37 ± 7 % in the AB scheme, at Q2 = 5 GeV2. The gluon contribution seems to be positive and within the range : 0 < DeltaG <2.Cette thèse décrit la mesure précise de la fonction de structure polarisée g1n du neutron menée par la collaboration E154 à l'automne 1995 auprès de l'accélérateur linéaire de Stanford aux Etats-Unis, par diffusion profondément inélastique inclusive d'un faisceau d'électrons polarisé de 48.3 GeV sur une cible d'Hélium 3 polarisée. Les électrons diffusés ont été détectés par deux spectromètres permettant de couvrir le domaine cinématique en x Bjorken : 0.014 < x < 0.7 et en quadritransfert carré : 1 GeV2 < Q2 < 17 GeV2 à une valeur moyenne Q2 = 5 GeV2. Deux calorimètres électromagnétiques pris en charge par le LPC de Clermont-Ferrand et le SphN du CEA-Saclay ont été utilisés pour déterminer l'énergie des électrons diffusés et pour rejeter le bruit de fond hadronique. Pour cela, nous avons développé un automate cellulaire et un réseau de neurones, largement décrits dans ce manuscrit. L'analyse de la mesure de la fonction de structure g1n menée à Clermont-Fd et exposée dans ce manuscrit nous a conduit à l'intégrale sur la région mesurée : intégrale (g1n(x)dx, xmin=0.0135, xmax=0.7) = -0.03 +- 0.003 STAT +- 0.004 SYST +- 0.001 EVOL à Q2 = 5 GeV2 où nous avons fait évoluer nos mesures vers Q2 = 5 GeV2 à l'aide des équations d'évolution DGLAP à l'ordre sous-dominant en utilisant une paramétrisation mondiale des distributions de partons polarisées. La règle de somme d'Ellis et Jaffe sur le neutron est clairement violée par nos mesures. Pour les différents extrapolations envisagées à bas x, notre intégrale est compatible avec la règle de somme de Bjorken. Nous avons estimé la contribution du spin des quarks au spin du nucléon à DelatSigma = 29 ± 6 % dans le schéma MS barre et à DeltaSigma = 37 ± 7 % dans le schéma AB, à Q2 = 5 GeV2. La contribution du spin des gluons au spin du nucléon semble positive et comprise entre 0 et 2 à cette échelle

Monte Carlo models of electron transport for dose-enhancement calculations in nanoparticle-aided radiotherapy

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Dosimetry simulations based on the GEANT4 toolkit : do it yourself !

International audienceThere is an obvious recurrent need in paleodosimetric dating methods to evaluate the doses delivered in various situations, for instance, when calibrating a source, calculating attenuation factors or directly determining dose-rates , etc ... and these evaluations are never simple and numerical simulations can then be of some help. For that purpose, we developped a flexible dosimetric tool named DosiVox. This software is based on the general purpose Geant4 Monte Carlo toolkit developed by an international collaboration for simulating particle-matter interactions. This tool allows to model a large variety of complex cases relevant to luminescence and ESR dating techniques and to perform dose-rate calculations useful for age determination. The user can create a model of the sample and its environment using a graphical interface which generates a pilot text file containing all the information relevant for the simulation. No skills in C++ programming or with the Geant4 libraries are then requir

3D micro-dosimetric simulation models with the Geant4 toolkit

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Geant4 Setups for archaeological samples

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Potential applications of the DosiVox software for dosimetry

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Geant4 dosimetric Setups for archeological objects

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DosiVox: Implementing Geant 4-based software for dosimetry simulations relevant to luminescence and ESR dating techniques

A C++ code, named DosiVox and based on the Geant4 Monte Carlo simulation toolkit, was developed in order to provide a reliable and flexible tool for modeling a large variety of situations of interest in paleodosimetric dating techniques, and for simulating interactions of usual particles (a, b and g) through complex geometries. DosiVox allows the user to define a three dimensional grid, in the simulation space whose voxel dimensions, materials and radioactive contents (U, Th, K) are set by a user-friendly graphical interface. No skills in C++ programming are required. Some of the possibilities offered by DosiVox are presented here through a series of examples