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Monte Carlo simulations of 250 keV photons effects on a 3D realistic mitochondria phantom and evaluation of radiation enhancement using gold nanoparticles

Abstract : In the field of radiobiology, damage to nuclear DNA is extensively studied since it is considered as a sensitive target inside cells. Mitochondria are starting to get some attention as sensitive targets as well since they control many functions important to the cell’s survival. They are double membraned organelles mainly in charge of energy production as well as reactive oxygen species regulation, cell signaling and apoptosis control. Some experiments have shown that after exposure to ionizing radiation the mitochondrial contents are altered and their functions are affected. That is why we are interested in studying the effects of ionizing radiation on mitochondria. At the microscopic scale, Monte Carlo simulations are helpful in reproducing the tracks of ionizing particles for a close study. Therefore, we produced 3D phantoms of mitochondria starting from microscopic images of fibroblast cells. These phantoms are easily uploaded into Geant4 as tessellated and tetrahedral meshes filled with water representing the realistic geometry of these organelles. Microdosimetric analysis is performed to deposited energy by 250keV photons inside these phantoms. The Geant4-DNA electromagnetic processes are used to simulate the tracking of the produced secondary electrons. Since clustered damages are harder to repair by cells, a clustering algorithm is used to study the spatial clustering of potential radiation damages. In radiotherapy, it is a challenge to deliver an efficient dose to the tumor sites without affecting healthy surrounding tissues. The use of gold nanoparticles as radio-sensitizers seems to be promising. Their high photon absorption coefficient compared to tissues deposit a larger dose when they are preferentially absorbed in tumors. Since gold has a high atomic number, Auger electrons are produced abundantly. These electrons have lower range than photoelectrons enabling them to deposit most of their energy near the nanoparticle and thus increasing the local dose. We studied the radio-sensitizing effect of gold nanoparticles on the mitochondria phantom. The effectiveness of this method is dependent on the number, size and spatial distribution of gold nanoparticles. After exposure to ionizing radiation, reactive oxygen species are produced in the biological material that contains abundant amount of water. In this study, we simulate the chemical species produced inside the mitochondria phantom and their clustering is estimated. We take advantage of the Geant4-DNA chemistry processes libraries that is recently included in the Geant4.10.1 release to simulate the spatial distribution of the chemicals and their evolution with time.
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https://tel.archives-ouvertes.fr/tel-01781525
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Submitted on : Monday, April 30, 2018 - 2:29:06 PM
Last modification on : Tuesday, January 15, 2019 - 3:03:37 PM
Long-term archiving on: : Thursday, September 20, 2018 - 2:09:27 AM

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2017CLFAC036_ZEIN.pdf
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  • HAL Id : tel-01781525, version 1

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Sara Zein. Monte Carlo simulations of 250 keV photons effects on a 3D realistic mitochondria phantom and evaluation of radiation enhancement using gold nanoparticles. Nuclear Experiment [nucl-ex]. Université Clermont Auvergne, 2017. English. ⟨NNT : 2017CLFAC036⟩. ⟨tel-01781525⟩

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