Inter- and intrascanner variability of pulmonary nodule volumetry on low-dose 64-row CT: an anthropomorphic phantom study

Objective: To assess inter- and intrascanner variability in volumetry of solid pulmonary nodules in an anthropomorphic thoracic phantom using low-dose CT. Methods: Five spherical solid artificial nodules [diameters 3, 5, 8, 10 and 12mm; CT density 1100 Hounsfield units (HU)] were randomly placed inside an anthropomorphic thoracic phantom in different combinations. The phantom was examined on two 64-row multidetector CT (64-MDCT) systems (CT-A and CT-B) from different vendors with a low-dose protocol. Each CT examination was performed three times. The CT examinations were evaluated twice by independent blinded observers. Nodule volume was semi-automatically measured by dedicated software. Interscanner variability was evaluated by Bland-Altman analysis and expressed as 95% confidence interval (CI) of relative differences. Intrascanner variability was expressed as 95% CI of relative variation from the mean. Results: No significant difference in CT-derived volume was found between CT-A and CT-B, except for the 3-mm nodules (p<0.05). The 95% CI of interscanner variability was within +/- 41.6%, +/- 18.2% and +/- 4.9% for 3, 5 and >= 8mm nodules, respectively. The 95% CI of intrascanner variability was within +/- 28.6%, +/- 13.4% and +/- 2.6% for 3, 5 and >= 8 mm nodules, respectively. Conclusion: Different 64-MDCT scanners in low-dose settings yield good agreement in volumetry of artificial pulmonary nodules between 5mm and 12mm in diameter. Inter- and intrascanner variability decreases at a larger nodule size to a maximum of 4.9% for >= 8 mm nodules. Advances in knowledge: The commonly accepted cut-off of 25% to determine nodule growth has the potential to be reduced for >= 8 mm nodules. This offers the possibility of reducing the interval for repeated CT scans in lung cancer screenings.