Abstract
ObjectivesAn 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.MethodsInstitutional 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 mm3) 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.ResultsOne hundred nodules (range 28–170 mm3; mean 81.1 mm3) were analysed. The lower and upper limits of agreement for the absolute volume difference between the two scans were − 14.2 mm3 and 12.0 mm3 respectively (mean difference 1.09 mm3, range − 33–12 mm3). 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%).ConclusionsThe 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.Key Points• In current pulmonary nodule management guidelines, a threshold of 25% increase in volume is required to determine that true growth of a pulmonary nodule has occurred.• This test–retest (coffee break) study has demonstrated that a smaller threshold of 15% increase in volume may represent true growth in small non-metastatic nodules.• Closer surveillance of some small nodules growing 15–25% over a short interval may be appropriate.
Highlights
Materials and methodsLung nodule growth is defined as an increase in nodule diameter or volume on sequential computed tomography (CT) scans and is a powerful predictor of lung malignancy [1, 2]
The British Thoracic Society (BTS) nodule management guidelines stipulate a 25% increase in nodule volume to determine growth [5], a threshold used in the Nederlands–Leuvens Longkanker Screenings Onderzoek (NELSON) lung cancer screening trial [6, 7]
Given that we found that the relative volume difference was approximately 15.5% either side of the mean nodule volume, and that any increase above this may represent true growth, we performed a further post hoc analysis to model how these results impact current nodule management guidelines for small nodules (Table 2)
Summary
Materials and methodsLung nodule growth is defined as an increase in nodule diameter or volume on sequential computed tomography (CT) scans and is a powerful predictor of lung malignancy [1, 2]. Establishing that true nodule growth has occurred can be challenging in cases where the increase in nodule size is small, due to the inherent limitations of measurement tools [3]. For this reason, many clinical practice guidelines stipulate that a minimum increase in nodule size must be achieved before nodule growth can be determined. The Fleischner Society guidelines stipulate that a threshold of 2-mm diameter growth should be used to define true nodule growth [4]. The British Thoracic Society (BTS) nodule management guidelines stipulate a 25% increase in nodule volume to determine growth [5], a threshold used in the Nederlands–Leuvens Longkanker Screenings Onderzoek (NELSON) lung cancer screening trial [6, 7]
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