[Accuracy of Effective Diameter and Water Equivalent Diameter Using Phantoms in Various CT Systems].

Abstract

Purpose: The effects of scanning parameters such as CT system performance, CT bed geometry, and upper limb position on effective diameter (ED) and water equivalent diameter (WED) have not been assessed. The purpose of this study was to compare both ED and WED obtained with various CT systems with theoretical values and to assess their accuracy.

Methods: Jaszczak cylindrical phantom (Data Spectrum, Durham, NC, USA), NEMA IEC body phantom (AcroBio, Tokyo), and thoracic bone phantom were used in this study with and without upper limb phantom. The ED, WED, and size-specific dose estimate (SSDE) obtained using 8 types of CT systems were computed using radiation dose control software.

Results: The EDs had <5% error for all systems, but the error increased as the aspect ratio of the phantom increased. The accuracy of WED varied depending on the CT systems, with a maximum difference of 3.57 cm between systems. The influence of the upper limb depended on the shape of the bed of the CT systems, which affected the correlation between ED as well as WED and SSDE.

Conclusion: Although the ED did not show any dependence on the CT system, the accuracy of WED for fusion CT was low. We found that there are issues in the management of scanning data, including the upper limb.