Evaluation of organ doses in paediatric computed tomography

Recently, a new method to estimate organ doses in computed tomography (CT) through scanner independent coefficients has been proposed with the purpose of providing one a fast dose estimation based on machine dose indicators. These dose coefficients are obtained normalizing organ doses by the CT dose index (CTDIvol) of the examination, and are assumed to be independent from the CT scanner. In order to validate experimentally these assumptions, organ doses measurements have been performed on an anthropomorphic paediatric phantom by means of thermoluminescent dosimeters. Doses measured in examinations performed with similar settings but different tomographs show a large variability, while CTDIvol normalized doses are less variable across scanners: the average coefficient of variation decreases from about 30% to about 10% after the normalization, thus confirming the assumption that organ doses in CT can be estimated by means of CT independent coefficients, both for helical and axial modes. Data obtained from measurements have also been compared with values calculated with different Monte Carlo based simulation tools, finding a good agreement between them.