Low-Dose CT (LDCT) for Lung Cancer Screening in Smokers
For lung cancer screening in smokers, use annual low-dose computed tomography (LDCT) scanning—not standard-dose CT or chest X-ray—as this is the only modality proven to reduce lung cancer mortality. 1, 2
Who Should Be Screened
Primary eligibility criteria based on the most recent USPSTF 2021 update:
- Age 50-80 years (expanded from previous 55-80 threshold) 1, 2
- ≥20 pack-year smoking history (reduced from previous 30 pack-year threshold) 1, 2
- Current smokers OR quit within past 15 years 1, 2
- No symptoms suggestive of lung cancer (symptomatic patients need diagnostic workup, not screening) 3, 4
- Adequate health to tolerate curative treatment if cancer detected 1, 2
The older NLST criteria (age 55-74, ≥30 pack-years) remain valid and represent the highest-quality evidence base, but the expanded criteria capture more at-risk individuals. 4
Alternative risk-based approach for patients not meeting standard criteria:
- Consider screening if validated risk calculator shows ≥1.51% 6-year risk (PLCOm2012 calculator) 2, 3
- This approach may be particularly useful for individuals with additional risk factors (COPD, pulmonary fibrosis, personal cancer history, family history of lung cancer, occupational exposures) 4
Technical Specifications
LDCT scan parameters must follow ACR/STR protocols: 4
- 120-140 kVp
- 20-60 mAs
- Average effective dose ≤1.5 mSv
- Collimation ≤2.5 mm 2
This is critical—standard-dose chest CT delivers significantly more radiation and is inappropriate for screening. 4
Screening Frequency and Duration
- Annual screening is the evidence-based interval 1, 2
- Continue annually until either: 1, 2
- Patient has not smoked for 15 years, OR
- Patient develops health problems substantially limiting life expectancy or ability/willingness to undergo curative surgery
Program Requirements
LDCT screening should only be performed within structured programs that include: 4
- Multidisciplinary expertise (pulmonary, radiology, thoracic surgery, medical/radiation oncology) 4
- Structured reporting system (LungRADS recommended) 4
- Established nodule management algorithms 4
- Mandatory smoking cessation counseling and treatment for current smokers 4, 5
- Shared decision-making visits before initial screening 4
Do not offer LDCT screening on an ad hoc individual basis—patients should be referred to dedicated screening programs with quality control. 4
Critical Caveats
Screening is NOT a substitute for smoking cessation—this must be emphasized to patients. 4, 2, 3
Common pitfalls to avoid:
- Screening patients <50 or >80 years old without compelling risk factors 4
- Using standard-dose CT instead of LDCT 4
- Screening symptomatic patients (they need diagnostic evaluation) 3, 4
- Screening patients with limited life expectancy who couldn't tolerate treatment 2, 3
- Performing screening outside structured programs without nodule management expertise 4
Harms to counsel patients about: 6, 2
- False-positive results are common (4-24% of scans) with 84-96% being false positives 7
- Overdiagnosis occurs in 19-69% of screen-detected cancers 7, 2
- Invasive procedures for false positives: 17 per 1000 screened in NLST 6
- Cumulative radiation exposure from annual screening 2, 4
- Incidental findings requiring follow-up (4.4-40.7% of persons screened) 6
Mortality benefit: LDCT screening reduces lung cancer mortality by 20% (NLST) to 25% (NELSON) in high-risk smokers, with an overall 12% reduction across trials. 1, 5, 7