<qa>  What is the average radiation dose?- CT scan group protocol Baseline and annual single-slice spiral CT are performed without contrast material, with a low-dose protocol, and reconstruction with lung algorithm at every 1 and 5 mm. The CT scanner is a 16 slice. Effective radiation dose is equivalent to 1.54 mSv milliSievert. Examinations are independently reported by two radiologists within 6 days, on a dedicated workstation and standard lung and mediastinum windows and maximum projection visual resolution reconstruction, for between-observer variability testing. A sophisticate algorithm for volumetric reconstruction and CAD Computer-Aided Detection software are used. Investigators deem calcified nodules or lesions with a maximum diameter of 5 mm measured on lung window non-suspicious and schedule repeat low-dose CT at next year, as per the protocol. Spiral thin-section CT limited to the area of interest and further examinations for growth assessment are completed within 3 months of baseline CT in every case of non-calcified lesion larger than 5 mm. Non-calcified lesions of 7 mm or larger, are tested with fluorine-18-labelled fluorodeoxyglucose PETpositron emission tomography and calculation of standardised uptake value. For each patient, the metabolic activity of the lung nodule is assessed by standardised uptake values, measured with regions of interest manually drawn around the nodule on transaxial images. 