Authors
1
M. Sc. in Medical Physics, Medical Physics Dept., Tarbiat Modarres University, Tehran, Iran.
2
Assistant Professor, Medical Physics Dept., Tarbiat Modarres University, Tehran, Iran.
3
Assistant Professor, Radiology Dept., Imam Khomeini Hospital, Tehran, Iran.
4
Associate Professor, Radiology Dept., Iran Medical Sciences University, Tehran, Iran.
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
Main Subjects
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