Data from: Reproducibility of volumetric computed tomography of stable small pulmonary nodules with implications on estimated growth rate and optimal scan interval

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.