Our group at the French Institute for Radioprotection and Nuclear Safety (IRSN) is working on the development of a method in order to improve knowledge of the risks of complications during radiotherapy treatments. It combines a Track Structure Monte Carlo (TSMC) simulation tool of the interactions of ionizing radiation and radiolytic species [1] based on Geant4-DNA [2, 3, 4, 5] with a multi-scale modeling tool of the exposed cell population based on new functionalities implemented in the DNAFabric software [6]. The benchmarking with experimental data [7] and the integration of mathematical functions derived from experimental biological data on cell fate in a broad sense is ongoing.