Evaluation of organ doses in paediatric computed tomography

In response to the concern arising from the increasing exposure of children to radiation delivered by computed tomography (CT), this work aims at evaluating doses delivered to a paediatric patient undergoing CT examinations. Recently, a method to estimate organ doses through scanner independent coefficients has been proposed, with the purpose to provide 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 supposed to be independent from the used CT scanner. In order to experimentally validate these assumptions, in-hospital measurements have been performed on an anthropomorphic paediatric phantom and doses have been measured by means of thermoluminescent dosimeters opportunely inserted in the dosimetric phantom. 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 assumptions, also for helical scans. Moreover, data obtained from measurements have been compared with values calculated with different Monte Carlo based simulation tools, finding a good agreement between them. Simulations have also been carried out to investigate the influence of examination settings and effects related to them.