Lung Cancer Screening (LCS) is a preventive health measure designed to detect malignant growths in the lungs before symptoms appear. The primary goal is to find lung cancer at its earliest possible stage, when treatment options are most effective and the potential for a cure is highest. LCS is specifically recommended for individuals considered to be at high risk for developing the disease, mainly due to their history of tobacco use. Detecting cancer early significantly improves the long-term survival rates for patients.
The Low-Dose CT Scan Procedure
The methodology used for Lung Cancer Screening is a Low-Dose Computed Tomography (LDCT) scan. This procedure utilizes an X-ray machine to capture multiple cross-sectional images of the chest, which a computer compiles to create a detailed, three-dimensional view of the lungs. The patient lies flat on a motorized table that slides into the circular opening of the CT scanner.
The scan is non-invasive, quick, and generally painless, often taking only a few minutes. Patients are asked to hold their breath briefly to ensure the clearest pictures. Unlike many other CT procedures, the LDCT scan does not require the injection of contrast dye.
The term “low-dose” signifies that the procedure uses a significantly reduced amount of radiation compared to a standard diagnostic chest CT scan. This minimal exposure is sufficient because the primary purpose is screening for small abnormalities, not detailed diagnosis. Using the lowest effective dose is a fundamental principle of medical imaging for an annual test like LCS.
Defining Screening Eligibility
Eligibility for Lung Cancer Screening is strictly defined by established medical guidelines to ensure the benefits outweigh the potential risks. The most widely recognized criteria are set by organizations like the U.S. Preventive Services Task Force (USPSTF), which recommends annual screening for a specific high-risk population, including adults between the ages of 50 and 80 years old.
The guidelines focus heavily on the individual’s smoking history, measured in “pack-years.” A pack-year is calculated by multiplying the average number of packs smoked per day by the number of years smoked. To qualify for screening, an individual must have a smoking history of 20 pack-years or more.
The final factor is current smoking status or how recently a person has quit. The individual must be a current smoker or a former smoker who quit within the last 15 years. Screening is discontinued once a person has not smoked for 15 years, reaches age 80, or develops a health condition that significantly limits life expectancy. These criteria were updated in 2021, lowering the starting age from 55 to 50 and the pack-year history from 30 to 20, which significantly expanded eligibility.
Interpreting Results and Next Steps
Once the LDCT scan is complete, a radiologist analyzes the images and assigns a result using the standardized Lung CT Screening Reporting and Data System (Lung-RADS). This system categorizes findings on a scale from 1 to 4, determining the likelihood of cancer and the appropriate next step. A score of Lung-RADS 1 indicates a negative result, meaning no suspicious nodules were found, and the patient returns for their next annual screening in 12 months.
A positive or suspicious result involves the detection of one or more pulmonary nodules. Most nodules discovered during LCS are benign, or not cancerous. The size, density, and growth rate of these nodules are the main factors used to place the finding into a higher Lung-RADS category, such as 3 or 4.
For a Lung-RADS 3 finding, which indicates a probably benign nodule with a low chance of malignancy, the recommended action is typically a short-term follow-up CT scan in six months to check for growth. Findings categorized as Lung-RADS 4A or 4B are more suspicious and may require a follow-up CT in three months, or a more invasive procedure like a biopsy, where a tissue sample is taken for testing. If the scan shows incidental findings unrelated to lung cancer, such as an aortic aneurysm or coronary artery calcification, the result may include an ‘S’ designation, indicating these require further medical evaluation.