Size and Growth Assessment of Pulmonary Nodules: Consequences of the Rounding

The aim of this study was to understand the effect of rounding nodule size measurements on the frequency of positive results in the setting of lung cancer screening.

Four methods for determining nodule size were compared, including rounding each individual length and width measurement and also rounding the overall average. These were applied to the International Early Lung Cancer Action Program database, in which we determined the frequency of a positive result by using standard size thresholds of 6.0 mm on baseline screening and 3.0 mm on repeat scanning. We also explored how rounding influences the ability to measure growth according to a predefined cutoff value of 1.5 mm as required in the Lung Computed Tomography Screening Reporting and Data System (Lung-RADS) (version 1.0).

Each method for rounding increased the frequency of positive results compared with that with no rounding. The largest increases-28.9% and 22.3% for the baseline and repeat round, respectively-occurred when rounding was used for both the individual length and width measurements and again for the final diameter. If the 1.5-mm increase in size were used for determining growth, a 4-mm nodule would need to have a volume doubling time of 130.6 days or less to demonstrate growth in 6 months (Lung-RADS category 3) whereas a 6-mm nodule would need volume doubling time of 93.2 days to demonstrate growth in 3 months (Lung-RADS category 4A). In addition, rounding can have the effect of having nodules that appear to not be growing meet the criteria for growth and vice versa.

Rounding influences the frequency of positive results and growth assessment, substantially decreasing the efficiency of screening.