Modeling and experimental validation of radiation-cellular media interactions in radiotherapy by photon activation of heavy elements
Résumé
An innovative approach using X-rays interactions with heavy elements seems to open a promising way of treatment for resistant cancers, such as high-grade gliomas. Such a technique is developed at the medical beam line of ESRF using monochromatic X-rays in the 50-100 keV range for the treatment of brain tumors [1,2]. The use of gold nanoparticles (GNP) to treat mice bearing subcutaneous tumors led to encouraging results [3]. However, the physical processes and biological impact of the photon activation of nanoparticles are not well understood. The experimental results cannot be explained from macroscopic dose calculations [4,5]. The aim of this study was to evaluate, at the cellular level, the dose enhancement in presence of nanoparticles and the properties of the secondary electrons production using the Monte Carlo transport code PENELOPE. The mean range, quantity and spectra of electrons produced from the interactions of X-rays with a GNP were calculated for 8 to 100 nm diameter GNP when irradiated with monochromatic photons from 30 keV to 2MeV. The dose enhancement was calculated in water at one micrometer around the GNP and in a cellular geometry considering homogeneous gold-water mixture. An increase of electron production by a factor 5 to 100 was observed in presence of GNP, for energies from 2 MeV to 30 keV respectively. The mean energy of the produced electrons increases with the beam energy, except after the K-edge of gold because of an enhancement of interactions with deeper atomic shells. An auto-absorption of low energy electrons for GNP with larger diameters was also observed. In the near future, we plan to calculate the dose in a cellular geometry considering multiple nanostructures.
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