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

Abstract

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 12 mm; 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 641.6%, 618.2% and 64.9% for 3, 5 and $8 mm nodules, respectively. The 95% CI of intrascanner variability was within 628.6%, 613.4% and 62.6% 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 5 mm and 12 mm 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.Lung cancer is the primary cancer in males and the second most common cancer in females worldwide, causing 18% of the total number of deaths [1]. Many lung cancers are found at a relatively late stage, resulting in a 5-year survival of only 15% or less [2]. Low-dose CT is a promising screening method for early detection of lung cancer [3][4][5][6][7]. The first result indicates that CT lung cancer screening can reduce lung cancer-specific mortality [8].

Quantification of growth patterns of screen-detected lung cancers: The NELSON study

“…In the NELSON study, slice thickness of 1.0 mm with reconstruction interval of 0.7 mm was used to provide isometric voxels for accurate semi-automated volume measurements. These semi-automated measurements were found to be highly reproducible for the large majority of solid nodules, also in phantom studies [27][28][29], with high reader agreement and volume differences >15% between two readers in only 4% of solid nodules [27][28][29]. Besides, in Lindell's study lung cancer growth curves were plotted and visually evaluated, but growth patterns were not quantified.…”

Final screening round of the NELSON lung cancer screening trial: the effect of a 2.5-year screening interval

“…For the screening, 16-detector or, in later rounds 64-detector CT scanners in low-dose setting were used, without the administration of intravenous contrast media. Images were analysed using semiautomated software (LungCARE, version Somaris/5 VA70C-W, Siemens Medical Solutions) 9 15. The analysis included the semiautomated segmentation of nodules and determination of the nodule volume.…”

“…Wang et al 17 showed that there was no benefit for double reading consensus with the use of semiautomated software. More detailed descriptions of the equipment and execution of the screening examination have been provided in previous reports 9 15 18…”

“…Briefly, in case of newly detected solid nodules and the solid component of part-solid nodules, the volume determined the screening result: <50 mm 3 was negative, 50–500 mm 3 was indeterminate and >500 mm 3 was positive 10 12 15 17 18. In case of previously detected nodules, evaluation was based on growth (defined as change in volume) and VDT.…”

Lung nodules: size still matters

“…A larger number of results derived from studies using newer generation scanners did not confirm the previous observations. Indeed, the introduction of iterative reconstructions, employed to increase image quality in favour of a further reduction of the effective radiation dose, demonstrated an even better performance compared to that of the traditionally used filtered-back projection reconstructions [101][102][103][104][105][106][107][108][109][110][111][112].…”