The goal of this axis is to provide new insights into simulation and image reconstruction methods for radiation therapy. Indeed, all types of radiation therapy treatments heavily rely on imaging, simulation and reconstruction methods, such as conventional external beam photon therapy, but also advanced hadrontherapy treatments with a proton or carbon ion beam, or molecular driven internal radiotherapy. In this axis, our group focuses on the development of new algorithms for numerical simulations of the physical processes involved during imaging and treatment (dosimetry), and novel reconstruction methods for innovative imaging systems. Among others, we developed activities related to advanced Monte Carlo simulation, variance reduction techniques, Deep Learning methods for Monte Carlo simulations, motion compensated image reconstruction, etc.