Modélisation du transport des électrons de basse énergie avec des modèles physiques alternatifs dans le code Geant4-DNA et application à la radioimmunothérapie

Abstract : During this PhD thesis, new developments have been brought to Geant4-DNA step-by-step Monte Carlo code. They were used to study low-energy electron interactions in liquid water – the major component of living organisms. The accuracy of results obtained through Monte Carlo code is limited by the validity of their cross sections. CPA100 is another step-by-step Monte Carlo code. It is equipped with ionization, electronic excitation and elastic scattering cross sections. However, these cross sections are calculated according to methods independent of those used for Geant4-DNA cross section calculations, which consisted of two original physics models: “option 2” and its improvement, “option 4”. Moreover, in some cases CPA100 cross sections are in better agreement with experimental data. Therefore, the first objective of this research was to implement CPA100 cross sections into Geant4-DNA in order to give users the choice of alternative physics models, known as Geant4-DNA-CPA100. They have been available to users since July 2017. The verification of the correct implementation of these physics models within Geant4-DNA involved a comparison of different basic quantities between Geant4-DNA-CPA100 and CPA100 and extremely similar results were obtained. For instance, a very good agreement was highlighted between the calculations of the track length and the number of interactions. Consequently, the impact of cross sections was assessed using the original Geant4-DNA physics models (“option 2” and “option 4”), the alternative Geant4-DNA-CPA100 physics models and PENELOPE code for calculations of useful quantities in nuclear medicine, such as dose-point kernels (DPKs for monoenergetic electrons) and S values (for monoenergetic electrons and Auger electron emitters). With regards to DPK calculations, Geant4-DNA with “option 2” and “option 4” physics models were in close agreement, showing a systematic difference with Geant4-DNA-CPA100, which in turn were close to those calculated with PENELOPE code. For S value calculations, however, Geant4-DNA results were in good agreement with Geant4-DNA-CPA100. Finally, in the context of radioimmunotherapy, energy depositions were mapped. Such simulations are usually performed assuming spherical tumor geometries and uniform monoclonal antibody distributions. Realistic data was extracted from an innovative 3D follicular lymphoma model incubated with antibodies. Energy depositions were calculated for Auger electron (111In and 125I) and - particle (90Y, 131I and 177Lu) emitters. It was demonstrated that - particle emitters delivered more energy and irradiated greater volume than Auger electron emitters. The most effective - particle emitter depends on the size of the model that is used.
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Julien Bordes. Modélisation du transport des électrons de basse énergie avec des modèles physiques alternatifs dans le code Geant4-DNA et application à la radioimmunothérapie. Modélisation et simulation. Université Paul Sabatier - Toulouse III, 2017. Français. ⟨tel-01847128⟩

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