With the aim of better understanding the mechanisms leading to side effects of radiotherapy and improving risk models, IRSN set up in 2010 the ROSIRIS research program. It requires the development of a predictive simulation tool of the associated risk depending on radiation quality. This simulation should take into account the different stages from the initial energy deposits arising from the interactions of ionizing radiation to late biological effects. The current simulation tool calculates radiation-induced DNA damage by inputting a realistic geometry of eukaryotic cell's DNA molecule into a nanodosimetric simulation chain based on the Geant4-DNA Monte Carlo toolkit. The simulations currently provide the mean number of strand breaks per track or per Gray in the cell nucleus and their complexity. Modeling of the fate of a population of monolayer cells is underway and involves extending the simulation to the cellular scale in order to obtain realistic topologies of radiation-induced DNA damage at the cellular population scale, while preserving the stochastic character of energy deposition for the irradiated cells.Calculating the damage distribution at the cell population scale with a nanodosimetric simulation chain is too long. Thus, we developed a method that combines microdosimetric and nanodosimetric information. Indeed, the specific energy seen by each cell of the population is computed from interpolations and transformations of monoenergetic spectra constituting a database. Once the z value and the corresponding tracks have been assigned to each cell of the cell population, nanodosimetric information is used to assign a radiation-induced DNA damage distribution to each cell.At present, the method for distributing the imparted energy, cell by cell, in the whole cell population has been developed for qualities of radiation which can combine charged particles ranging from 1 keV to 20 MeV. A comparison with the microdosimetric distributions in the cells obtained by a Monte-Carlo simulation is in progress. In this work, the irradiation corresponds to an exposure by a monoenergetic neutron beam of 14.5 MeV irradiating a cell culture of endothelial cells placed in front of a water phantom. The method we have developed and the validation results are presented.< Réduire