International audienceAn 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. The use of gold nanoparticles 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 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.At first, upstream studies were done around the behavior of gadolinium and gold nanoparticles (GdNP and AuNP) under irradiation. Then dose calculations were done in a cellular geometry containing gadolinium-water mixture in order to compare with experimentations realized on the ID17 beamline of ESRF