TITLE:
Comparison of Planer Dose Equilibrium and Computed Tomography Dose Index and Implications for Reported Patient Dose Information
AUTHORS:
Ahmad Albngali, Joshua Deslongchamps, James Blackwell, Andy Shearer, Brendan Tuohy, Niall Colgan
KEYWORDS:
CT Dosimetry, CTDI Method, DEq Method, CT Scanner
JOURNAL NAME:
Open Journal of Medical Imaging,
Vol.9 No.4,
November
6,
2019
ABSTRACT: Technical developments are ongoing in CT, and there has been a continually
increasing trend in patient prescription, resulting in increased exposure.
Currently, doses delivered during CT are generally evaluated using computed
tomography dose index (CTDI), which is measured with a 10 cm pencil ionization
chamber placed in a 14 cm PMMA phantom. However, shortfalls in
CTDI have been identified by the American Association of Physicists in
Medicine (AAPM) who have proposed a new method, dose equilibrium
(DEq). In this paper, the dose equilibrium was used to estimate the dose in
two protocols (thoracic and abdominopelvic) and compared to CTDI values.
In addition, a retrospective correction was applied to 20 patient CTDI’s by
characterizing the specific DEq profile of the system scans. The results indicated
the dose equilibrium estimations of two protocols, thoracic and abdominopelvic,
were 29% and 30% respectively, higher than those informed by
the CT scanner. In addition, a retrospective dose correction estimation of a
random sample of twenty patients demonstrated an annual underestimation
in absorbed dose by between 26% and 28%. Continued use of the CTDI method
in quality assurance of modern CT could result in greater patient risk.
AAPM Task Group 111 presents a more accurate, safer method to estimate
dose and its adoption is paramount.