Minimum Detectable Change in Lung Nodule Volume in a Phantom CT Study

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The change in volume of lung nodules is being examined as a measure of response to treatment. The aim ofthis study was to determine the minimum detectable change in nodule volume with the use of computed tomography. Four different layouts of synthetic nodules with different shapes but with the same size (5, 8, 9, or 10mm) for each layout were placed within an anthropomorphic phantom and scanned with a 16-detector-row computed tomography scanner using multiple imaging parameters. Nodule volume estimates were determined using a previously developed matched-filter estimator. Analysis of volume change was then conducted as a detection problem. For each nodule size, the pooled distribution of volume estimates was shifted by a percentage c to simulate a changing nodule, while accounting for standard deviation. The value of c resulting in a prespecified area under the receiver operating characteristic curve (AUC) was deemed the minimum detectable change for that AUC value. Both nodule size at baseline and choice of slice collimation protocol had an effect on the value of minimum detectable growth. For AUC=0.95, the minimum detectable nodule growth in volume when using the thin-slice collimation protocol (16×0.75mm) was 17%, 19%, and 15% for nodule sizes of 5, 8, and 9mm, respectively. Our results indicate that an approximate bound for detectable nodule growth in subcentimeter nodules may be relatively small, on the order of 20% or less in volume for a thin-slice CT acquisition protocol.