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2014 ; 41
(4
): 042102
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Sample size requirements for estimating effective dose from computed tomography
using solid-state metal-oxide-semiconductor field-effect transistor dosimetry
#MMPMID24694150
Trattner S
; Cheng B
; Pieniazek RL
; Hoffmann U
; Douglas PS
; Einstein AJ
Med Phys
2014[Apr]; 41
(4
): 042102
PMID24694150
show ga
PURPOSE: Effective dose (ED) is a widely used metric for comparing ionizing
radiation burden between different imaging modalities, scanners, and scan
protocols. In computed tomography (CT), ED can be estimated by performing scans
on an anthropomorphic phantom in which metal-oxide-semiconductor field-effect
transistor (MOSFET) solid-state dosimeters have been placed to enable organ dose
measurements. Here a statistical framework is established to determine the sample
size (number of scans) needed for estimating ED to a desired precision and
confidence, for a particular scanner and scan protocol, subject to practical
limitations. METHODS: The statistical scheme involves solving equations which
minimize the sample size required for estimating ED to desired precision and
confidence. It is subject to a constrained variation of the estimated ED and
solved using the Lagrange multiplier method. The scheme incorporates measurement
variation introduced both by MOSFET calibration, and by variation in MOSFET
readings between repeated CT scans. Sample size requirements are illustrated on
cardiac, chest, and abdomen-pelvis CT scans performed on a 320-row scanner and
chest CT performed on a 16-row scanner. RESULTS: Sample sizes for estimating ED
vary considerably between scanners and protocols. Sample size increases as the
required precision or confidence is higher and also as the anticipated ED is
lower. For example, for a helical chest protocol, for 95% confidence and 5%
precision for the ED, 30 measurements are required on the 320-row scanner and 11
on the 16-row scanner when the anticipated ED is 4 mSv; these sample sizes are 5
and 2, respectively, when the anticipated ED is 10 mSv. CONCLUSIONS: Applying the
suggested scheme, it was found that even at modest sample sizes, it is feasible
to estimate ED with high precision and a high degree of confidence. As CT
technology develops enabling ED to be lowered, more MOSFET measurements are
needed to estimate ED with the same precision and confidence.