In the Dutch-Belgian randomized lung cancer screening trial (NELSON), launched in 2003, 7557 participants in the screening arm underwent low-dose chest CT scanning. The design of the NELSON trial including participant selection and lung nodule management have been published previously (1, 2). The NELSON trial was approved by the Dutch Minister of Health and the ethics board of each participating center. All participants gave written informed consent.

The CT scanning protocol consisted of four screening rounds each using a 16-detector CT scanner (three Sensation-16, Siemens Medical Solutions, Forchheim, Germany and one Brilliance 16P, Philips Medical Systems, Cleveland, OH, USA). Non-contrast low dose CT scans of the entire chest were obtained in a cranio-caudal direction in one breath hold (about 12 s in spiral mode with 16 x 0.75 mm collimation and pitch 1.3). The kVp setting in the NELSON were depending of the patient body weight (<50 kg, 50–80 kg and >80 kg) : 80–90 kVp, 120 kVp and 140 kVp respectively (1).

For this retrospective study, all participants in whom non-calcified nodules were detected at the baseline screening examination (between April 2004 and December 2006) were included. The number of prevalent nodules was determined per participant. Nodule volumes were calculated semi-automatically in Syngo LungCare software. Lung cancer diagnosis was confirmed by histology.

Descriptive statistics were determined with SPSS Statistics version 22 (IBM, Armonk, NY) and mentioned as number and percentage. Comparisons were made using chi-square testing.