Potential for CT dose reduction based on QA phantom and human cadaver images

Abstract

Purpose: CT centres having higher radiation doses when compared to many CT centres locally and internationally have been identified through a nationwide dose survey carried in Nigeria for CT examinations of the brain, chest and abdomen. This provides a basis for dose reduction methods to be explored. This study proposes a methodology using a quality assurance (QA) phantom and human cadaver images.

Materials and methods: The study proposes a methodology consisting of three phases. Phase I: Manipulation of scan parameters to monitor their effect on radiation dose indices and psycho-physical parameters using a GE QA phantom, leading to determination of the optimal parameter settings. Phase II: Application of the identified optimal QA phantom protocols on the human cadaver as a starting point for further optimisation, which was followed with analysis of results based on VGA, VGC and VGR from evaluation of cadaveric images. Phase III: Clinical implementation of the finally optimised protocols and further image quality evaluation based on VGA, VGC and VGR.

Results: Fifteen adult QA optimised protocols were established in five CT centres. Of the 15 QA phantom protocols, nine protocols from three centres were tested on cadaver as two of the centres did not give permission for cadaver scanning. Of the nine protocols, six were further optimised as three protocols could not be further optimised due to severe loss of image quality. Furthermore, two of the six cadaver optimised protocols, were not implemented due to the radiologists preference of image quality, rather the established QA optimised protocols were retained which still achieved dose reduction when compared to standard protocols. The implemented optimised protocols in two of the three CT centre showed evidence of dose reductions based on the new CTDIvol DRLs as follows: 36% for brain; 18% for chest and 21% for abdomen, whilst the DLPs were: 44% for brain, 54% for chest and 30% for abdomen with acceptable image quality based on the VGA, VGC and VGR. Conclusion: The study established optimised protocols in selected CT centres providing acceptable image quality based on the VGA, VGC and VGR using a methodology with a lot of advantages such as low cost resources (QA phantom and human cadaver) which is ideal for countries lacking expensive equipment (Catphan and anthropometric phantoms).