Effect of smoking cessation on quantitative computed tomography in smokers at risk in a lung cancer screening population

To longitudinally evaluate effects of smoking cessation on quantitative CT in a lung cancer screening cohort of heavy smokers over 4 years. After 4 years, low-dose chest CT was available for 314 long-term ex-smokers (ES), 404 continuous smokers (CS) and 39 recent quitters (RQ) who quitted smoking within 2 years after baseline CT. CT acquired at baseline and after 3 and 4 years was subjected to well-evaluated densitometry software, computing mean lung density (MLD) and 15th percentile of the lung density histogram (15TH). At baseline, active smokers showed significantly higher MLD and 15TH (-822 +/- 35 and -936 +/- 25 HU, respectively) compared to ES (-831 +/- 31 and -947 +/- 22 HU, p < 0.01-0.001). After 3 years, CS again had significantly higher MLD and 15TH (-801 +/- 29 and -896 +/- 23 HU) than ES (-808 +/- 27 and -906 +/- 20 HU, p < 0.01-0.001) but also RQ (-813 +/- 20 and -909 +/- 15 HU, p < 0.05-0.001). Quantitative CT parameters did not change significantly after 4 years. Importantly, smoking status independently predicted MLD at baseline and year 3 (p < 0.001) in multivariate analysis. On quantitative CT, lung density is higher in active smokers than ex-smokers, and sustainably decreases after smoking cessation, reflecting smoking-induced inflammation. Interpretations of quantitative CT data within clinical trials should consider smoking status.