Research presented at the 2026 AAPM Annual Meeting by Nicolas Pineda, DMP, DABR; Alyssa Martinez, MS; and Renee Butler, MS
Size-specific dose estimate has earned its place as the preferred CT dose index for body imaging. CTDIvol tells you what the scanner delivered to a reference phantom. SSDE, per AAPM TG 204 and TG 220, corrects for patient size and tells you something closer to what the patient actually received. Radiation dose index monitoring (RDIM) platforms have adopted it widely, and newer scanners now display series-level SSDE on the console before the scan, calculated from the scout.
That console display opens a practical point: If technologists are going to use scanner-reported SSDE prospectively to judge whether a scan’s dose is appropriate for the patient on the table, that number needs to agree with the SSDE the RDIM system calculates independently from the RDSR. CAMP’s Nicolas Pineda, Alyssa Martinez, and Renee Butler put that agreement to the test in a study presented at this year’s AAPM Annual Meeting.
The Study
The team extracted SSDE values from 384 abdomen/pelvis exams across two platforms, a Siemens X.Cite (n=299) and a Canon Aquilion One (n=85), pulling scanner-reported values from the RDSR and comparing them against SSDE calculated by Imalogix. Exams were sorted into Imalogix’s patient-size categories based on effective diameter, from XXS through XXL, and evaluated both collectively and within size groups. Agreement was assessed with the Wilcoxon Signed Rank Test and visualized with Bland-Altman plots.
What They Found
The two SSDE sources are statistically different (p<0.05), but the practical difference is small. The median difference was 3.9%, and Bland-Altman plots showed average differences under 2 mGy across all groups. Agreement was tightest for small patients and degraded as patient size increased, with the largest deviations, around 22%, occurring at very large patient sizes.
One pattern held across the dataset: scanner-reported SSDE ran consistently lower than the RDIM value. That directionality matters. A technologist checking the console before scanning is working with a slightly conservative number relative to what the RDIM system will log, which supports using the console display for prospective dose assessment rather than undermining it.
Why It Matters
This is where SSDE earns its keep over CTDIvol. For body imaging, CTDIvol gives the technologist no useful read on whether a particular scan will under- or over-expose a particular patient. A size-corrected metric on the console, checked against protocol-specific SSDE targets and thresholds, turns dose appropriateness into a real-time decision instead of a retrospective finding in next month’s dose committee review.
The study’s takeaway for practicing physicists: scanner and RDIM-reported SSDE are similar enough to be used together in a dose monitoring program, with the caveat that agreement weakens for the largest patients. If your facility scans a heavy bariatric population, that 22% tail is worth understanding before you set thresholds around either number.
What’s Next
The team’s future work includes validating both scanner and RDIM-reported SSDE against image-based calculations using phantom scans, extending the comparison to additional scanners and exam types, and building out technologist education so that reviewing SSDE before scanning becomes standard practice rather than a physicist-only exercise.
Questions about the study or about building SSDE into your CT dose monitoring program? Contact us at CAMP.
References
- AAPM. (2011). Size-Specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations. AAPM Report No. 204.
- AAPM. (2014). Use of water equivalent diameter for calculating patient size in CT. Report of AAPM Task Group 220.
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Last updated: August 2026
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