With the growing use of computed tomography (CT) in children and the increasing awareness of CT radiation risk to this population, there is a greater need to accurately estimate radiation dose from CT examination for the purpose of assessing life-time cancer risk and also for the comparing and optimizing CT technologies and scan protocols. The knowledge of dose delivered to individual organs is fundamental for risk estimates. In the absence of techniques to measure organ doses directly from patients, the following methods based on patient phantoms and models to estimate organ and effective doses will be used in this project: Experimental measurements and Monte Carlo (MC) simulations. From the measurements results obtained in phantom and by verification of measurements by MC simulation it will be possible to prepare the sets of calculated data for children of different ages and consequently the evaluation of the risk for paediatric population could be possible