The identification and invitation of participants will be carried out using a multimodal approach: local and national press campaigns, outreach to insured individuals aged 50 to 74 in certain regions, and through an ambassador network (healthcare professionals, institutional representatives, associations, and citizens aware of lung cancer screening).

Screening support tools will be deployed, including:

• A website with a calculator to help determine eligibility;
• A telephone call center to assess eligibility.

Inclusions :

Inclusions will be carried out by the participant's primary care physician if they are an investigator, or by other volunteer general practitioners, in health centers; by secondary care providers; or via outreach programs.

The inclusion visits or teleconsultations will allow verifying the eligibility criteria and obtaining electronic consent.

The participation rate is defined as the number of individuals having performed at least one CT scan, divided by the number of eligible individuals.

The investigators will measure the participation rate to follow-up invitations following an indeterminate CT scan result

The investigators will measure the participation rate to screening at 1 year and 3 year

For participants with a positive screening result, the procedures, results, and complications of diagnostic actions (PET, endoscopy, CT-guided or ultrasound-guided biopsy, surgery) will be collected from the participants' medical records .

The rate of early-stage lung cancers among the lung cancers diagnosed following a CT screening will also be measured (Evaluation criterion: number of lung cancers diagnosed at stage I or II divided by the total number of diagnosed lung cancers).

The investigators will record the proportion of active smokers who either decline the systematically offered smoking-cessation assistance or fail to attend the scheduled appointment, as well as the factors underlying this refusal. The investigators will also assess smoking cessation rates during follow-up and identify their predictors.

The investigators will record the proportion of active smokers who declined smoking-cessation support or did not attend the scheduled appointments

Investigators will collect the reasons selected by participants for refusing smoking cessation support from a pre-established list (e.g., concern about weight gain, fear of failure).

The investigators will assess smoking cessation rates during follow-up and identify their predictors.

The investigators will identify the predictor of smoking cessation rates (correlation with age, gender, level of education, occupation, etc…)

• Agreement in classifying cases as "screen-negative" versus "positive or indeterminate" between a single AI-assisted reading and a double AI-assisted reading (with a third adjudication in case of disagreement, serving as the reference), measured using the kappa coefficient.
• Agreement in classifying cases as "screen-negative" versus "positive or indeterminate" between AI alone and the reference, measured using the kappa coefficient.

For each of these anomalies, the detection rate will be calculated as the number of participants with the anomaly divided by the number of participants who underwent at least one CT scan. The presence and severity of emphysema (Fleischner classification), the Shemesh score, attenuation at the T8 level, and the diameter of the ascending aorta if >4 cm will be systematically recorded in the structured CT screening report. Interstitial lung abnormalities (ILA, including Langerhans cell histiocytosis), osteoporotic compression fractures, and all anomalies requiring clinical care will also be systematically documented.

The impacts on care pathways can be measured by evaluating the following time intervals,

-Time between registration on the platform and completion of the inclusion visit,

• Time between inclusion and completion of the initial CT scan,
• Time until availability of radiology reports (single and double reading),
• Time to first contact with a tobacco cessation specialist

AND Using the date of the CT scan as the reference date:

• Time to presentation of positive cases at the MDTB,
• Time to a positive diagnosis (pathological report or MDTB report )
• Time to first treatment for positive cases requiring it,
• Time to the first thoracic surgery consultation,
• Time to surgery
• Time to other consultations depending on incidental findings

Healthcare utilization will be compared between screening-adherent and non-adherent patients, using two different denominators: the target population and the invited population after linkage with the SNDS (French National Health Data System).

As part of the IMPULSION study, an imaging dataset for research and teaching purposes will be created, including all CT scans performed during the study (baseline, follow-up, and subsequent screening rounds), unless the participant explicitly objects.

Using the variables collected in the IMPULSION study, a predictive lung cancer risk score will be developed for the eligible population, specifically tailored to the French population.

The costs associated with screening (including surgical treatment of early-stage cancers and hospitalization for invasive procedures) will be compared with the costs that would have been incurred if the screen-detected lung cancers had all been diagnosed at an advanced stage.

The objective of this sub-study is to conduct a qualitative analysis of the characteristics of participants in lung cancer screening and the program.

Qualitative assessment of participant perceptions regarding lung cancer screening in a random sample of 2,000 participants enrolled in the main study.

The objective is to assess whether this dose level, using modern techniques, provides information equivalent to that obtained with the dose used in the main protocol.

A second ultra-low-dose acquisition (CTDI 0.15 mGy for weight < 80 kg, CTDI 0.20 mGy for weight ≥ 80 kg) immediatly after the IMPULSION CT scan.

The ultra-low-dose CT scan will be read exclusively in a centralized manner by a certified radiologist assisted by AI software, using the same criteria as those applied to the low-dose reference acquisition, and blinded to the low-dose CT data.

An assessment of concordance will be performed in 2,500 participants.

Collection of a maximum of 28 mL of whole blood (i.e., approximately 7 tubes of 5 mL with 4 mL collected per tube) for storage for research purposes.

The collected samples are intended to create a biobank linked to clinical and radiological data. This biobank will make it possible to test various biomarkers for predicting individual cancer risk, the risk that a nodule is cancerous, or the risk of developing a disease evaluated in this cohort (including COPD, cardiovascular disease, osteoporosis, or interstitial lung disease).

The purpose of this examination is to assess lung volumes at inclusion visit.

In participating an optional, spirometry will be performed at inclusion. The following mesaures will be recorded : FEV1 and FVC.

Interpretation will be based on GOLD recommendations and using the GLI system for reference values.

The following definitions will be used:

• Pre-COPD: FEV₁ < 80% and FEV₁/FVC ≥ 0.7
• Obstructive ventilatory defect (OVD): FEV₁/FVC < 0.7 on spirometry
• GOLD stages 1 to 4 according to the FEV₁ value. Participant questionnaire will also includes questions about chronic COPD symptoms in order to assess the presence of a COPD.