Room: Exhibit Hall | Forum 9
Purpose: To investigate the effect of image truncation on the calculation of water equivalent diameter (WED) and size-specific dose estimates (SSDE).
Methods: A set of 286 thorax and 222 abdomen non-truncated CT images were analysed by the dose management system DOSE (Qaelum, Belgium) and the WED and SSDE were provided. Next, the canvas size of the images was symmetrically cropped to different percentages and the effective truncation percentages (TP: ratio of patient border touching image edges to total patient border) were calculated. The WEDtruncated and SSDEtruncated from the truncated images were computed and compared with the initial non-truncated values. The percentage differences were evaluated for thorax (PDthx) and abdomen (PDabd) examinations.
Results: For small TP (<10%), the SSDEtruncated did not differ from the initial SSDE for 95% of thorax and 98% of abdomen exams. The number of patients with higher SSDEtruncated than initial SSDE increased for TP from 10% to 40%, however application of correction factors on WED reduced this number and improved the SSDE calculation (fig). For TP 40%-50%, the SSDEtruncated was different from SSDE for a large number of cases for both the thorax and abdomen data (98% and 92% respectively). Correction for WED improved the calculation for thorax but not for abdomen. Additionally, for symmetrical truncation up to 50%, the correction of WED had a positive result, while for non-symmetrical truncation, correcting WED does not seem to be enough for accurate results, especially for TP>30%.
Conclusion: When a CT image is truncated to a high percentage, the wrongly calculated WED will result to an increased SSDE and consequently to an increased number of dose alerts, especially when the used protocol is close to the trigger levels for dose notifications. In some cases, this can be minimized if correction factors are applied to WED before SSDE is calculated.
Funding Support, Disclosures, and Conflict of Interest: N. Fitousi: Medical Physicist and Head of Research Qaelum NV A.S.L. Dedulle: Employee; Qaelum NV. Research/Grant Support; VLAIO grant No. HBC.2016.0233 J. Jacobs: CEO and Co-founder Qaelum NV H. Bosmans: Board Member and Co-founder Qaelum NV