Reproducibility of Volumetric Computed Tomography of Stable Small Pulmonary Nodules with Implications on Estimated Growth Rate and Optimal Scan Interval.

Smith GT, Rahman AR, Li M, Moore B, Gietema H, Veronesi G, Massion PP, Walker RC
PLoS One. 2015 10 (9): e0138144

PMID: 26379272 · PMCID: PMC4575025 · DOI:10.1371/journal.pone.0138144

PURPOSE - To use clinically measured reproducibility of volumetric CT (vCT) of lung nodules to estimate error in nodule growth rate in order to determine optimal scan interval for patient follow-up.

METHODS - We performed quantitative vCT on 89 stable non-calcified nodules and 49 calcified nodules measuring 3-13 mm diameter in 71 patients who underwent 3-9 repeat vCT studies for clinical evaluation of pulmonary nodules. Calculated volume standard deviation as a function of mean nodule volume was used to compute error in estimated growth rate. This error was then used to determine the optimal patient follow-up scan interval while fixing the false positive rate at 5%.

RESULTS - Linear regression of nodule volume standard deviation versus the mean nodule volume for stable non-calcified nodules yielded a slope of 0.057 ± 0.002 (r2 = 0.79, p<0.001). For calcified stable nodules, the regression slope was 0.052 ± 0.005 (r2 = 0.65, p = 0.03). Using this with the error propagation formula, the optimal patient follow-up scan interval was calculated to be 81 days, independent of initial nodule volume.

CONCLUSIONS - Reproducibility of vCT is excellent, and the standard error is proportional to the mean calculated nodule volume for the range of nodules examined. This relationship constrains statistical certainty of vCT calculated doubling times and results in an optimal scan interval that is independent of the initial nodule volume.

MeSH Terms (12)

Adult Aged Cone-Beam Computed Tomography False Positive Reactions Female Humans Lung Male Middle Aged Multiple Pulmonary Nodules Reproducibility of Results Retrospective Studies

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