An assessment of the Doses Received by Children from CT Examinations Along with the QC Parameters from a Conventional CT System

Abstract

Introduction: In 2000, the UNSCEAR reported that CT constitutes 5% of all the medical x-ray <br /> examinations and it contributes 34% of the resultant collective dose worldwide. Children are more <br /> sensitive to the ionizing radiations than adults. So, routine quality control tests are expected to be <br /> carried out periodically on the CT scanners. The aim of this research was to estimate the effective <br /> doses received by the children below two years of age from routine CT examinations carried out <br /> at an educational imaging center in Tehran. It was also aimed to evaluate the quality control <br /> parameters of the mentioned CT scanner at the same time. <br /> Materials and Methods: In this study, the Computed Tomography Dose Index (CTDI) values <br /> were measured at the central axis of the CT gantry in air and in the standard quality control <br /> phantoms of the head and body (as recommended by the FDA) using a pencil ionization chamber <br /> and LiF TLD pellets for a single scan. By using the measured CTDI values and the ImPACT <br /> software, the effective doses were calculated for every routine CT examination protocol. In this <br /> study, the quality control parameters such as noise, CT number calibration, high and low contrast <br /> resolution and the flatness of the CT image were also evaluated. These parameters were also <br /> measured using standard procedures and test objects. <br /> Results: The effective dose estimated in this research ranged from 2.05 to 21.45 and 2.05 to 15.7 <br /> mSv for the female and male children, respectively. The measured values of the CTDI in the <br /> standard head and body phantoms were 20.6 ± 2.01 and 11.13 ± 1.04 mGy/100 mAs, respectively. <br /> The high and low contrast resolution was estimated to be 0.8 mm and 1.0 mm, respectively. <br /> Conclusion: The estimated values of the effective doses in this research were less than the values <br /> reported for the Netherlands, the USA, Germany and were comparable with the values reported in <br /> the UK. The measured CTDI values were 11% more than that of the ImPACT. Although the <br /> estimated doses are comparable with the ones from other countries, but the quality control tests <br /> indicated that the CT number was not calibrated as well as the lack of uniformity in CT numbers. <br /> An acceptable calibration of the CT scanner not only could provide high quality images, but it <br /> could also lead to a lesser patient dose hence abiding by the ALARA principle in radiation <br /> protection.