What are the parameters for lung cancer screening using low-dose computed tomography (LDCT)?

Lung Cancer Screening Parameters

Annual low-dose CT screening should be performed for adults aged 50-80 years with ≥20 pack-year smoking history who currently smoke or have quit within the past 15 years, using specific technical parameters and nodule size thresholds to optimize mortality benefit while minimizing harms. 1, 2

Eligibility Criteria

Primary Age and Smoking-Based Criteria

The most current evidence supports broader screening criteria than previously recommended:

• Adults aged 50-80 years with ≥20 pack-year smoking history who currently smoke or have quit within the past 15 years should undergo annual LDCT screening 1, 2
• The older criteria (age 55-80 years with ≥30 pack-years) are no longer optimal, as modeling studies demonstrate that lowering the threshold to 20 pack-years increases lung cancer deaths averted from 381 to 469-558 per 100,000 and life-years gained from 4,882 to 6,018-7,596 per 100,000 3
• Screening should continue annually until the person has not smoked for 15 years 1, 2

Alternative Risk-Based Criteria

For individuals who don't meet standard age/smoking criteria:

• Consider screening if validated risk calculators show ≥1.51% 6-year risk on PLCOm2012 calculator or ≥1.33% 5-year risk on LCDRAT calculator 4
• Risk-based approaches may improve screening efficiency and reduce disparities across race and sex compared to simple age/smoking criteria 4

Absolute Contraindications

Do not screen individuals with:

• Significant comorbidities that substantially limit life expectancy or ability to tolerate curative lung surgery (e.g., advanced liver disease, COPD with hypoventilation and hypoxia, NYHA class IV heart failure) 5, 1
• Symptoms suggesting lung cancer (hemoptysis, unexplained weight loss >6.8 kg in preceding year) - these patients require diagnostic testing, not screening 5, 4
• Quit smoking >15 years ago without other high-risk features 1

Technical Specifications for LDCT

Specific scanner parameters must be followed:

• Multidetector CT scanner with ≥4 channels 5
• Voltage: 120-140 kVp 5, 1
• Current: 20-60 mAs 5, 1
• Average effective radiation dose: ≤1.5 mSv 5, 1
• Collimation: ≤2.5 mm 5, 1

Nodule Management Thresholds

The definition of a positive screen is critical to balance sensitivity and false-positives:

• Nodules ≥5 mm require 3-month follow-up LDCT (limited scan covering only the nodule area to reduce radiation) 5, 1
• Nodules ≥15 mm require immediate diagnostic workup to rule out malignancy 5, 1
• The 5 mm threshold is preferred over the 4 mm threshold used in NLST, as it reduces false-positive baseline scans from >27% to <20% while still detecting early-stage curable cancers 5

Common pitfall: The NLST used a 4 mm threshold, but this resulted in 96% false-positive rates among positive screens 5. The 5 mm threshold substantially reduces unnecessary workup without compromising cancer detection.

Screening Interval and Duration

• Annual screening is the standard interval 1, 2
• Continue screening through age 80 years unless contraindications develop 1, 2
• Discontinue once the person has not smoked for 15 years 1, 2

Implementation Requirements

Screening must occur in specialized centers with:

• Multidisciplinary expertise in lung cancer diagnosis and treatment 5, 1
• Established protocols for nodule follow-up and diagnostic procedures 5
• Capability to provide smoking cessation counseling alongside screening 1, 4

Critical caveat: Ad hoc screening outside experienced centers leads to increased false-positive rates and periprocedural morbidity/mortality, potentially negating screening benefits 5.

Key Harms to Counsel Patients About

• Radiation exposure: Cumulative dose from annual screening, though benefit-risk ratio is approximately 10:1 for women and 25:1 for men 6
• False-positives: Estimated 1.9-2.5 false-positive results per person screened with optimized criteria 3
• Overdiagnosis: Approximately 83-94 indolent cancers per 100,000 screened 3
• Procedural complications: Death within 60 days of diagnostic evaluation occurs in 8 per 10,000 individuals screened 5

Essential Patient Counseling

Screening is not a substitute for smoking cessation - active cessation counseling must accompany all screening programs 1, 4