Diagnostic radiation represents an indispensable, sometimes life-saving, tool in modern medicine. However, the growing use of computerized tomography (CT) is a topic of concern in radiological protection, especially for children and adolescents. Children are generally more sensitive to the carcinogenic effects of ionizing radiation than adults. In addition, they have a longer life-span to express any effect and, because of their smaller mass, they may receive higher radiation doses from a CT scan than an adult.A large-scale multinational collaborative study will be set up with the objective of providing guidance towards optimisation of doses from paediatric CT scans. We have the following specific aims: 1) describe the pattern of use of CT in different countries and over time; 2) derive individual estimates of organ doses ; 3) assess biological markers of CT-irradiation effects; 4) directly evaluate radiation-related risk of cancer following CT; and 5) characterize the quality of CT images in relation to the estimated doses in order to better inform CT imaging practice.Scientists from nine European countries with expertise in epidemiology, clinical practice, radiology, dosimetry, biology and public health will contribute to the project with the objective of provide recommendations for a “harmonized” approach to CT dose optimisation for paediatric patients in Europe. Results of this research will serve to increase awareness of the scientific and medical communities about public health aspects related to the use of diagnostic radiation and to provide recommendations on the use of valuable diagnostic tools, with lowering the risk of its potential hazards as much as possible.