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

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. 

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Main Subjects

Iranian Journal of Medical Physics
Volume 2, Issue 3 - Serial Number 3
September and October 2005
Pages 31-44

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History

  • Receive Date: 04 June 2005
  • Revise Date: 10 July 2005
  • Accept Date: 20 August 2005

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