X Li*, T Marschall, K Yang, B Liu, Harvard Medical School, Massachusetts General Hospital, Boston, MA

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  X Li

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TU-D1000-IePD-F8-4 (Tuesday, 7/12/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 8

Purpose: A method was previously proposed to calculate the average dose to the transverse slab of an axial image slice (Dslice) for adult body CT, considering scan length, mA profile, and patient DW profile, with proof of concept – calculation results compared with Geant4 simulation for a single patient with chest and abdominopelvic exams. In this study, we calculate Dslice for two exams of a cohort of 65 patients and compare the results with the previous Geant4 simulation results [Dsim(z)].

Methods: In each exam, each axial image slice (slice thickness, 2.5 or 5 mm) was considered a sub-scan range just covering the slice, whose CTDIvol (from the DICOM headers) was used to directly calculate a z-axis dose profile for the average dose over the cross section of a water phantom, using the approach to equilibrium function. The phantom diameter was equal to the patient water equivalent diameter (DW) at that slice. The above was repeated at all slices and the dose at each z-axis location was accumulated from all profiles, referred to as Dcalc(z).

Results: Dcalc(z) evaluation could be used to accurately assess scan range average dose, with an accuracy of 7.1–8.7% for 65 patients in two exams. On individual image slices, the maximum difference in magnitude between Dcalc(z) and Dsim(z) was 37.5% [two edges (2×5 cm) of chest scan range], 17.8% (the remaining central region of chest scan), 26.8% [two edges (2×5 cm) of abdominopelvic scan range], and 14.2% (the remaining central region of abdominopelvic scan).

Conclusion: The method may provide accurate evaluation of scan range average dose, reasonable estimate of Dslice, and assistance to CT manufacturers and dose index monitoring software in assessing Dslice for body CT scans. Dcalc(z) may also facilitate dose estimation for the organs completely inside, partially inside, or completely outside a scan range.

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