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A Comparison Between NCRP-147 Workload Values and Calculated Workload Values for a Large Collimation CT Scanner in An ED
D Vergara*, M Yester , UAB Medical Center, Birmingham, AL
Presentations
TU-C2-GePD-IT-1 (Tuesday, August 1, 2017) 10:00 AM - 10:30 AM Room: Imaging ePoster Theater
Purpose: Since the publication of Report #147 of the National Council on Radiation Protection and Measurements (NCRP-147) in 2004, computed tomographic scanners (CTs) have undergone a rapid technological advancement. CT scanners now have larger scan coverage per gantry rotation; protocols include current modulation, and other dose sparing capabilities. Such changes to imaging protocols result in a reduction in radiation dose to the patient and lower radiation to the surrounding area. A retrospective study was conducted to determine how large coverage CTs with modern imaging protocols affect the CT workload and scatter, as compared to established parameters published in NCRP-147.
Methods: Data was collected from the DICOM headers of patient CT image sets acquired for two weeks using an individual Phillips Brilliance iCT 256 in the ED and averaged for one week. CTDI-vol, scan length and DLP were compared to the values found within NCRP-147. Scatter fractions (κ-body) as a function of collimation were also calculated for the CTDI body phantom from scattered air kerma measurements (K-meas) for different collimations and isocenter positions within the phantom.
Results: The DLP values for body procedures were approximately 40% lower than NCRP-147 values. The scatter fraction (cm⁻¹) varied as a function of collimation and position of radiation isocenter within the phantom. For 80-mm and 40-mm coverage, there was 100% and 50% variation of K-meas, respectively, along the length of the CTDI body phantom.
Conclusion: As expected, shielding thicknesses using the NCRP-147 formalism for CT scanner shielding calculations would be quite conservative for modern scanners with iterative reconstruction and dose modulation. If one utilizes the scatter plots produced by CT vendors for shielding calculation, one needs to be aware of the collimation used for the scatter measurements and placement of the beam isocenter relative to the phantom center.
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