Research objectives and content The Monte-Carlo (MC) metllod enables computer simulation of the particle tracks of radiations such as high-energy photons and electrons through arbitrarily complicated geometries without physical approximations using random numbers and atomic cross-section data. The extraordinary speed and affordability of today's computers makes such MC-based simulation a realistic basis for radiotherapy treatment planning. I will be using the well documented EGS4 MC code and writing routines to track particles through the three-dimensional geometry of radiotllerapy accelerators and patient anatomy. The objective is a major improvement in the accuracy of radiation dose delivery in patients undergoing external-beam radiotherapy (roughly I in 7 EU citizens), especially in the highly inhomogeneous thorax and head and neck regions. This worlc is being conducted in collaboration with a treatment planning system manufacturer and will thus result in the widespread use of is new computation method in European cancer clinics. Training content (objective, benefit and expected impact) My background is in dosimetry, radicbiology and MC modelling. Through this project will receive a training at a world-class research centre in the exciting field of MC-based radiotherapy. Linlcs with industry / industrial relevance (22) The scientist in charge is collaboratrogYadh DOSIGlLlY, a french StIE vnth a major European market share in radiotherapy treatment planning systems (l PS). The resulting Monte-Carlo-based TPS should be a world first.