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Applying three different methods of measuring CTDIfree air to the extended CTDI formalism for wide-beam scanners (IEC 60601-2-44): A comparative study
KTH, School of Engineering Sciences (SCI), Physics. Karolinska Univ Hosp, Med Radiat Phys & Nucl Med, Stockholm, Sweden.
Sunderby Hosp, Dept Radiat Phys, Lulea, Sweden..
KTH, School of Engineering Sciences (SCI), Physics.ORCID iD: 0000-0002-3039-9791
Umea Univ, Dept Radiat Sci, Umea, Sweden..
2018 (English)In: Journal of Applied Clinical Medical Physics, ISSN 1526-9914, E-ISSN 1526-9914, Vol. 19, no 4, p. 281-289Article in journal (Refereed) Published
Abstract [en]

Purpose: The weighted CT dose index (CTDIw) has been extended for a nominal total collimation width (nT) greater than 40 mm and relies on measurements of CTDfree air. The purpose of this work was to compare three methods of measuring CTDIfree air and subsequent calculations of CTDIw to investigate their clinical appropriateness. Methods: The CTDIfree air, for multiple nTs up to 160 mm, was calculated from (1) high-resolution air kerma profiles from a step-and-shoot translation of a liquid ionization chamber (LIC) (considered to be a dosimetric reference), (2) pencil ionization chamber (PIC) measurements at multiple contiguous positions, and (3) air kerma profiles obtained through the continuous translation of a solid-state detector. The resulting CTDIfree air was used to calculate the CTDIw, per the extended formalism, and compared. Results: The LIC indicated that a 40 mm nT should not be excluded from the extension of the CTDIw formalism. The solid-state detector differed by as much as 8% compared to the LIC. The PIC was the most straightforward method and gave equivalent results to the LIC. Conclusions: The CTDIw calculated with the latest CTDI formalism will differ most for 160 mm nTs (e.g., whole-organ perfusion or coronary CT angiography) compared to the previous CTDI formalism. Inaccuracies in the measurement of CTDIfree air will subsequently manifest themselves as erroneous calculations of the CTDIw, for nTs greater than 40 mm, with the latest CTDI formalism. The PIC was found to be the most clinically feasible method and was validated against the LIC.

Place, publisher, year, edition, pages
Wiley , 2018. Vol. 19, no 4, p. 281-289
Keywords [en]
computed tomography, computed tomography dose index, dosimetry
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
URN: urn:nbn:se:kth:diva-232623DOI: 10.1002/acm2.12363ISI: 000437835600034PubMedID: 29900670Scopus ID: 2-s2.0-85049641917OAI: oai:DiVA.org:kth-232623DiVA, id: diva2:1235994
Funder
The Karolinska Institutet's Research Foundation
Note

QC 20180730

Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2018-07-30Bibliographically approved

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