CT Screening for Lung Cancer: Alternative Definitions of Positive Test Result Based on the National Lung Screening Trial and International Early Lung Cancer Action Program Databases

Purpose: To determine the usefulness of alternative nodule size thresholds in a population undergoing computed tomographic (CT) screening for lung cancer and to compare the reported International Early Lung Cancer Action Program (I-ELCAP) results with the National Lung Screening Trial (NLST) results. Materials and Methods: The institutional review board approved this retrospective analysis. Informed consent was obtained according to HIPAA compliance. Findings in the CT cohort in the NLST of 25 813 participants who underwent baseline CT in 2002-2004 were reviewed. The frequency of solid and part-solid pulmonary nodules and the lung cancer diagnoses using an alternative nodule threshold of 5.0, 6.0, 7.0, 8.0, and 9.0 mm were determined. Proportional reduction in the frequency of positive results and their 95% confidence intervals using each of the alternative thresholds were calculated. Results: The frequency of positive results in the baseline round in the CT arm of the NLST using the definition of a positive result of any parenchymal, solid or part-solid, noncalcified nodule of 5.0 mm or larger was 15.8% (4080 of 25 813). Using alternative thresholds of 6.0, 7.0, 8.0, and 9.0 mm, the frequencies of positive results were 10.5% (2700 of 25 813, 7.2% (1847 of 25 813), 5.3% (1362 of 25 813), and 4.1% (1007 of 25 813), respectively, and the corresponding proportional reduction in additional CT scans would have been 33.8% (1380 of 1480), 54.7% (2233 of 4080), 66.6% (2718 of 4080), and 73.8% (3013 of 4080), respectively. Concomitantly, the proportion of lung cancer diagnoses determined within the first 12 months would be delayed up to 9 months for 0.9% (two of 232), 2.6% (six of 232), 6.0% (14 of 232), and 9.9% (23 of 232) of the patients, respectively. Conclusion: The NLST results are similar to those previously reported for the I-ELCAP and suggest that, even for high-risk participants in the NLST, higher thresholds of nodule size should be considered and prospectively evaluated. (C) RSNA, 2014