What are the indications for low-dose computed tomography (CT) scan of the chest in smokers?

From the Guidelines

Low-dose computed tomography (CT) scan of the chest is recommended for lung cancer screening in high-risk smokers, specifically those aged 55-77 years with a 30 pack-year smoking history who currently smoke or have quit within the past 15 years. The primary indication for low-dose CT scan of the chest in smokers is to reduce lung cancer-related mortality by detecting more patients in earlier, potentially curable stages 1. A pack-year is calculated by multiplying the number of packs smoked per day by the number of years smoked. For example, smoking one pack daily for 30 years or two packs daily for 15 years both equal 30 pack-years.

Key Considerations

• The screening should be performed annually until the person has either quit smoking for more than 15 years, reaches 80 years of age, or develops a health condition that significantly limits life expectancy or the ability to undergo curative lung surgery 1.
• Low-dose CT is preferred over conventional chest X-rays because it can detect smaller lung nodules and has been shown to reduce lung cancer mortality by 20-24% in high-risk populations 1.
• The radiation exposure from low-dose CT is significantly less than standard CT scans, making it safer for repeated annual screenings while still providing sufficient image quality to detect early-stage lung cancers when treatment is most effective 1.
• A process of informed and shared decision-making with a clinician related to the potential benefits, limitations, and harms associated with screening for lung cancer with low-dose computed tomography should occur before any decision is made to initiate lung cancer screening 1.

Additional Recommendations

• Smoking cessation counseling remains a high priority for clinical attention in discussions with current smokers, who should be informed of their continuing risk of lung cancer 1.
• The American College of Radiology Appropriateness Criteria recommend lung cancer screening with low-dose CT for patients between the age of 55 and 80 with 30 or more pack years smoking history who currently smoke or who have quit within the last 15 years 1.

From the Research

Indications for Low-Dose CT Scan of the Chest in Smokers

The indications for low-dose computed tomography (CT) scan of the chest in smokers are based on the risk of developing lung cancer. According to the studies, the following are the indications:

• High-risk smokers, defined as those aged 55 to 74 years with ≥ 30 pack-years of smoking and who quit ≤ 15 years prior to entry if ex-smokers 2
• Heavy smokers, defined as those with > 20 pack-years of smoking and aged > 40 years 3
• Current or former smokers with ≥ 30 pack-years of smoking, aged 55 to 74 years 4

Benefits of Low-Dose CT Scan

The benefits of low-dose CT scan in smokers include:

• Detection of asymptomatic, early, resectable lung cancers 3, 5, 4
• Reduction in lung cancer mortality in high-risk smokers 2, 4
• High sensitivity for small pulmonary nodules, which are the most common manifestation of early lung cancer 5, 6

Screening Algorithms

The screening algorithms for low-dose CT scan in smokers include:

• Nodule density, size, and demonstration of growth at follow-up to correctly classify detected lesions and avoid invasive procedures in benign nodules 5
• Algorithms based on size and density of detected nodules to avoid unnecessary biopsies in benign lesions 6
• Consideration of nodules < 5 mm as negative findings, nodules > 10 mm as positive, and intermediate nodules between 5 and 10 mm for 3-month CT scan with doubling time measurement 4