This study was an Institutional Review Board approved, consent-waived retrospective data analysis of kidney stone CT exams (KS-CT) performed in our Institution from March 2017 through March 2018 (1 year period).
Two 3rd generation 128 and 256 slice CT scanners (Philips; Ingenuity 128 and iCT 256, respectively) were installed in our emergency-department (ED) from March 2017. Dedicated KS-CT protocols utilized on non-ED scanners in our department were adapted to ED-CT scanners (mAS=180, DRI=19, kV=100-120). Images were reconstructed using Model Based Iterative Reconstruction (MBIR) algorithm.
Doses were monitored using automated dose monitoring software (DoseWise, Philips).
Initial assessment of KS-CT exams was performed within 7 months of ED-CT scanner installation. A total of 1330 KS-CT exams were performed at our institution during this period and 399 exams (30%) were performed on ED-CT scanners (Group A).
KS-CT radiation doses (DLP: mGy-cm) were compared across different CT scanners, ED and non-ED scanners from same or different vendors (Non-ED Philips (Spectral, Philips 256) exams= 718 (54%) and Siemens Somatom= 199 exams (14%)). Doses were also compared across different CT technologists.
KS-CT doses for ED-CT scanners were higher than Institutional averages (Group A, mean DLP=784, Non-ED scanners=612) (Figure 1). Causes of dose variability were further investigated. It was noted that in a majority of cases, CT technologists were selecting CT Abd-Pelvis protocol for performing KS-CT exams, which in part was due to no dedicated ED KS-CT protocol specific for new CT scanners.
Subsequently, protocols were further optimized congruent to the CT technology/ iterative reconstruction (IR) algorithm and a dedicated ED KS-CT protocol implemented for routine clinical practice from Nov 2017.(Figure 2) The new optimized KS-CT protocol included following scan parameters mAs=57, DRI=13-15 and kV=100-120. (Figure 3) CT technologists were updated of the protocol changes and encouraged to be compliant with the new ED KS-CT protocol.
Finally, KS-CT radiation doses for ED scanners were re-evaluated in March 2018 (within 4 months of protocol changes) to assess for the performance of protocol optimization and technologist education. Radiologists ensured diagnostic acceptability of images at the time of dictation and any IQ issue were reported.
The data was stored and analyzed in Microsoft Excel.
Over all, 598 KS-CT exams were performed within 1 year following installation of ED-CT scanners. A total of 399 exams were performed within 7 months of installation (Group A, M:F=201,198; mean age=55) and 199 exams were performed following protocol optimization and technologist education (Group B, M:F=99,100; Mean Age= 58 years). (Figure 3)
Substantial dose reduction of 45% were noted in Group-B compared to Group A (mGy-cm; Group-A= 794, Group-B=454). (Figure 3) Doses were 16-40% lower than Institutional and National averages (American College of Radiology, Dose Index Registry). (Figure 4) There were considerable (10X) decrease in number of exams performed with DLP exceeding 1000 mGy-cm in Group-B (% exams above 1000 mGy-cm: Group-A=24.6%; Group-B=2.5%). Exams with doses <300mGy-cm drastically (25X) increased in Group-B (% exams below 300mGy-cm, Group-A=1.3, Group-B=26.1). (Figure 5,6) Overall, nearly 80% of exams were performed with DLP less than 500 mGy-cm in Group B, drastic decrease compared to Group A (only 17% exams). (Figure 4) Dose reduction showed comparable trend with substantial decrease in mean and Max DLP within all CT technologists in Group B compared to Group A. (Figure 7)