Open AccessApplying three different methods of measuring CTDI free air to the extended CTDI formalism for wide‐beam scanners ( IEC 60601–2–44): A comparative study
Author(s) -
Bujila Robert,
Kull Love,
Danielsson Mats,
Andersson Jonas
Publication year - 2018
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1002/acm2.12363
Subject(s) - kerma , ionization chamber , dosimetry , formalism (music) , physics , nuclear medicine , detector , ionization , optics , medicine , ion , musical , art , quantum mechanics , visual arts
Purpose The weighted CT dose index ( CTDI w ) has been extended for a nominal total collimation width ( nT ) greater than 40 mm and relies on measurements of C T D I f r e e a i r. The purpose of this work was to compare three methods of measuring C T D I f r e e a i rand subsequent calculations of CTDI w to investigate their clinical appropriateness. Methods The C T D I f r e e a i r, for multiple nT s 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 C T D I f r e e a i rwas used to calculate the CTDI w , per the extended formalism, and compared. Results The LIC indicated that a 40 mm nT should not be excluded from the extension of the CTDI w 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 CTDI w calculated with the latest CTDI formalism will differ most for 160 mm nT s (e.g., whole‐organ perfusion or coronary CT angiography) compared to the previous CTDI formalism. Inaccuracies in the measurement of C T D I f r e e a i rwill subsequently manifest themselves as erroneous calculations of the CTDI w , for nT s 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.