Defining growth in small pulmonary nodules using volumetry: results from a coffee-break CT study and implications for current nodule management guidelines

Objectives An increase in lung nodule volume on serial CT may represent true growth or measurement variation. In nodule guidelines, a 25% increase in nodule volume is frequently used to determine that growth has occurred; this is based on previous same-day, test-retest (coffee-break) studies examining metastatic nodules. Whether results from prior studies apply to small non-metastatic nodules is unknown. This study aimed to establish the interscan variability in the volumetric measurements of small-sized non-metastatic nodules. Methods Institutional review board approval was obtained for this study. Between March 2019 and January 2021, 45 adults (25 males; mean age 65 years, range 37-84 years) with previously identified pulmonary nodules (30-150 mm(3)) requiring surveillance, without a known primary tumour, underwent two same-day CT scans. Non-calcified solid nodules were measured using commercial volumetry software, and interscan variability of volume measurements was assessed using a Bland-Altman method and limits of agreement. Results One hundred nodules (range 28-170 mm(3); mean 81.1 mm(3)) were analysed. The lower and upper limits of agreement for the absolute volume difference between the two scans were - 14.2 mm(3) and 12.0 mm(3) respectively (mean difference 1.09 mm(3), range - 33-12 mm(3)). The lower and upper limits of agreement for relative volume difference were - 16.4% and 14.6% respectively (mean difference 0.90%, range - 24.1-32.8%). Conclusions The interscan volume variability in this cohort of small non-metastatic nodules was smaller than that in previous studies involving lung metastases of varying sizes. An increase of 15% in nodule volume on sequential CT may represent true growth, and closer surveillance of these nodules may be warranted.

Automated summary

In this study, the interscan volume variability of small non-metastatic nodules was found to be smaller than in previous studies involving lung metastases. The average relative difference in volume between two same-day CT scans was 0.90%, with a lower limit of -16.4% and upper limit of 14.6%. Therefore, an increase of 15% in nodule volume on sequential CT may indicate true growth, requiring closer surveillance.