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

Keywords

• CT
• Effective dose
• CTDI
• Quality control
• Children
• Patient dose
• Phantom