Program Information
Methodology for Establishing CT Dose Monitoring Alert Levels as a Function of Patient Size for Protocols Using Tube Current Modulation
K Krugh1*, S Gallo2 , (1) University of Toledo Medical Center, Toledo, OH, (2) The Toledo Hospital, Toledo, OH
Presentations
TH-EF-601-10 (Thursday, August 3, 2017) 1:00 PM - 3:00 PM Room: 601
Purpose: Users of CT dose monitoring software generally set fixed, examination-specific dose index thresholds for triggering “high dose” alerts. For protocols that use tube current modulation (TCM), this can lead to false-positive alerts for very large patients and to no alerts for smaller-sized patients who receive scans with significantly higher dose indices than typical of the examination. We developed an analytical method for establishing CT dose monitoring alert level threshold curves as a function of patient size for CT protocols that use TCM.
Methods: Patient water-equivalent diameter (WED) and corresponding scanner-reported CTDIvol was exported from Radimetrics™ dose monitoring software for multiple CT scan protocols that use TCM across three different CT vendors. The data was separated by scanner and scan protocol into multiple data sets. An empirically-derived model based upon the logistic function was fit to each data set to obtain a set of optimal fit parameters. The fit parameters were then modified to obtain an alert level threshold curve as a function of WED.
Results: The logistic function provides an accurate model for the relationship between WED and CTDIvol when TCM is in use as displayed by fit R² values exceeding 0.9 for all data sets. The alert level threshold curves derived from the fit parameters made it simple to accurately identify examinations with significant dose outliers and excluded those which, in the past, have been attributed solely to “large patient size”. Several of the dose outliers identified with the alert level threshold curves were investigated and found to have unwarranted reasons for the large dose deviation (e.g., TCM deactivated, inappropriate scan protocol selected, scan outside of localizer limits, modification of kVp or rotation time).
Conclusion: Use of this methodology to establish patient-size-based alert level threshold curves will improve the quality and value of the CT dose monitoring task.
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