Participants will undergo a chest CT scan in the Department of Radiology at Tianjin Cancer Hospital. All scans will be performed using the same CT system: Definition AS. Two readings of the images will be performed. In the first image reading, the CT images will be read by specially trained Chinese resident radiologist and checked by one of two senior Chinese radiologists. Lung Cancer Screening (version 2. 2018) Guidelines of the National Comprehensive Cancer Network (NCCN) will be used for the management of lung nodules. This guideline recommends management of lung nodules based on diameter. In the second reading, a semi-automated volumetry software will be used to measure the volume and evaluate the other parameters of lung nodules.

At baseline and one year after baseline, data about general characteristics, risk factors of lung cancer, and health status of the participants will be collected.

In the first reading, according to the NCCN lung cancer screening guideline, participants with a solid nodule≤ 5 mm in diameter will be referred to undergo follow-up CT 1 year after the baseline. Participants with a solid nodule 6-14 mm will be referred to undergo follow-up thorax CT 3-6 months after the baseline. Participants with a solid nodule ≥ 15 mm will be referred to a multidisciplinary team for clinical investigation.

The simulated management will be based on the volume of lung nodule and volume doubling time from the second reading, lung nodules will be reclassified according to the reference values from the European volume-based lung nodule management protocol. According to the European volume-based protocol, the solid and part-solid lung nodules will be reclassified into three groups: nodules with a volume < 100 mm3 (negative), nodules with a volume of 100-300 mm3 (indeterminate), and nodules with a volume > 300 mm3 (positive).

The number of clinically diagnosed lung cancer will be collected through the hospital information system and by contacting the participants or their relatives using a questionnaire.

The number of lung cancer death will be collected through the hospital information system and by contacting the relatives of the participants using a questionnaire.