Impact of Dose on 3D Volumetric Scout Scan Water‑Equivalent Diameter Determination
Abstract
Purpose
Canon Healthcare Systems USA has recently introduced a volumetric planning scan, known as the 3D Landmark, designed to support automatic exposure control (AEC), automated anatomical landmark detection for scan planning, and patient positioning. This acquisition uses silver beam filtration to substantially reduce patient dose by removing lower‑energy x‑rays. The purpose of this study is to quantify the effect of radiation dose on the accuracy of water‑equivalent diameter (WED) measurements derived from the 3D Landmark scan.
Methods
A Sun Nuclear Mercury 4.0 phantom containing multiple sections of varying water‑equivalent diameters was scanned on a Canon Aquilion One Insight system using the 3D Landmark protocol (pitch 1.39, 40‑mm collimation, 0.5‑s rotation, 120 kV, silver filtration). These scan parameters are fixed within the protocol; only tube current is adjustable. The phantom was scanned at tube currents corresponding to CTDIvol values ranging from 0.1 mGy (10 mA) to 3.2 mGy (700 mA). A reference scan without silver filtration was acquired at 41.9 mGy CTDIvol. WED was measured in each phantom section and compared across dose levels. Microsoft Copilot assisted with the preparation of this abstract.
Results
Across both the smallest and largest phantom sections, WED measurement error remained below 3 mm relative to the reference scan. Although WED accuracy was maintained, image quality is significantly degraded in the scans.
Conclusion
Despite substantial image quality degradation at very low doses, WED measurements derived from the 3D Landmark volumetric planning scan remained robust across a wide dose range in this phantom. These results suggest that low‑dose volumetric scouts with silver filtration can reliably support patient‑size assessment for AEC. Future work will evaluate the limits of WED accuracy in larger phantoms.