In the United States, lung cancer remains the leading cause of cancer death, causing more deaths each year than breast, colorectal, and prostate cancers combined. Lung cancer can also develop without noticeable symptoms, which is one reason screening can be important for people at high risk.
For eligible individuals, low-dose CT (LDCT) screening of the chest can detect lung cancer at an earlier, more treatable stage.
What Is Low-Dose CT Lung Screening and Why Does It Matter?
Low-dose CT lung screening uses a low-radiation-dose CT scan of the chest to create detailed images of the lungs and look for early signs of lung cancer. It can detect small pulmonary nodules that may not be visible on a standard chest X-ray.
A landmark U.S. study, the National Lung Screening Trial (NLST), included more than 53,000 people at high risk for lung cancer. Screening with low-dose CT resulted in a 20% relative reduction in lung-cancer mortality compared with chest X-ray screening.
Who Should Get Screened?
Eligibility for lung cancer screening varies by country, guideline, smoking history, age, and individual health factors.
For example, the U.S. Preventive Services Task Force recommends annual low-dose CT screening for adults aged 50 to 80 years who have at least a 20 pack-year smoking history and currently smoke or have quit within the past 15 years. Screening should generally stop once a person has not smoked for 15 years or develops a health condition that substantially limits life expectancy or the ability or willingness to undergo curative treatment.
How Much Radiation Does Low-Dose CT Use?
Low-dose CT is specifically designed to reduce radiation exposure while maintaining image quality suitable for lung cancer screening. Typical effective doses are approximately 1.5 mSv for a lung cancer screening CT compared with around 6.1 mSv for a conventional chest CT, although the actual dose varies according to the scanner, protocol, and patient.
Because screening involves repeated imaging over time, keeping radiation exposure as low as reasonably achievable is an important part of a well-designed screening programme.
What Happens If Something Is Found?
Finding a pulmonary nodule does not mean that a person has lung cancer. Most nodules detected through screening are benign. In the National Lung Screening Trial, 96.4% of positive low-dose CT screening results were ultimately classified as false positives.
Radiologists commonly use the American College of Radiology’s Lung-RADS system to standardise lung cancer screening findings and follow-up recommendations.
- Lung-RADS 1 or 2: Negative or benign-appearing findings, generally followed by annual low-dose CT screening.
- Lung-RADS 3: Probably benign findings, typically followed with another low-dose CT in 6 months.
- Lung-RADS 4A: Suspicious findings, generally requiring short-term follow-up, commonly with a 3-month low-dose CT. PET/CT may be considered for certain nodules.
- Lung-RADS 4B or 4X: More suspicious findings that may require further diagnostic imaging, specialist evaluation, PET/CT, tissue sampling, or another appropriate investigation depending on the individual case.
The appropriate next step depends on the size, appearance, growth pattern, and other characteristics of the finding, as well as the patient’s clinical history.
Screening Is Not a Replacement for Quitting Smoking
A normal screening scan does not eliminate the future risk associated with smoking. Smoking cessation remains one of the most important ways to reduce the risk of developing lung cancer and many other serious diseases.
People who currently smoke and participate in lung cancer screening should also be offered support to stop smoking.
Why Expert Interpretation Matters
Accurate interpretation is an important part of lung cancer screening. Radiologists assess the size, density, appearance, and change over time of pulmonary nodules and may compare the scan with previous imaging when available.
Some lung cancer screening programmes also have specific qualification and experience requirements for interpreting physicians. For example, U.S. Medicare coverage criteria include requirements relating to radiology qualifications, chest CT experience, and continuing medical education.
If you or a loved one has had a lung CT and would like additional clarification about the findings, an independent radiology second opinion may provide another specialist interpretation.
A specialist radiologist can review the available CT images and report remotely when a second opinion is appropriate. This can be particularly useful when a pulmonary nodule is unclear, previous imaging needs comparison, or an important treatment or follow-up decision depends on the imaging findings.
References
- National Lung Screening Trial Research Team. Reduced Lung-Cancer Mortality with Low-Dose Computed Tomographic Screening. N Engl J Med. 2011;365:395–409. doi:10.1056/NEJMoa1102873
- U.S. Preventive Services Task Force. Lung Cancer: Screening. Final Recommendation Statement. USPSTF recommendation
- American College of Radiology. Lung CT Screening Reporting & Data System (Lung-RADS), Version 2022. ACR Lung-RADS
- Fintelmann FJ, Bernheim A, Digumarthy SR, et al. The 10 Pillars of Lung Cancer Screening: Rationale and Logistics of a Lung Cancer Screening Program. RadioGraphics. 2015;35(7):1893–1908. doi:10.1148/rg.2015150079
- Ono K, Hiraoka T, Ono A, et al. Low-dose CT scan screening for lung cancer: comparison of images and radiation doses between low-dose CT and follow-up standard diagnostic CT. SpringerPlus. 2013;2:393. doi:10.1186/2193-1801-2-393
