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

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.