Are all computed tomography (CT) lung screens done with low-dose contrast?

CT Lung Screening is Performed Without Contrast

CT lung screening should always be performed without contrast as a low-dose CT scan to minimize radiation exposure while maintaining diagnostic accuracy for lung nodule detection. 1

Technical Specifications for Lung Cancer Screening CT

Lung cancer screening CT scans are specifically designed to be low-dose examinations that balance the need for adequate image quality with radiation safety concerns. According to the American College of Radiology (ACR) guidelines:

• CT lung screening must be performed as a non-contrast helical (spiral) study 1
• Radiation dose should be ≤3 mGy for standard-sized patients 1
• Images should be acquired at ≤2.5-mm slice thickness (with <1 mm preferred) 1
• Multi-slice CT scanners are preferred, though single-slice helical scanners can be used 1
• Typical technical parameters include:
  • 120 kVp
  • 40 mA with 6:1 pitch (for GE scanners) or 20 mA with 7:1 pitch (for Siemens scanners)
  • 1-1.25 mm slice thickness
  • 0.5 second rotation time 1

Why Contrast is Not Used in Lung Cancer Screening

There are several important reasons why contrast is not used in lung cancer screening:

1. Nodule detection efficacy: Non-contrast CT is highly effective for detecting pulmonary nodules, which is the primary goal of screening 1, 2
2. Radiation dose concerns: Adding contrast would increase radiation exposure, contradicting the "as low as reasonably achievable" principle 1
3. Cost and resource considerations: Non-contrast studies are less expensive and do not require IV access or monitoring for contrast reactions
4. Evidence base: The National Lung Screening Trial (NLST) and other major screening trials that demonstrated mortality benefit used low-dose non-contrast CT 2, 3

Performance of Low-Dose CT Without Contrast

Low-dose CT without contrast has demonstrated excellent performance metrics in lung cancer screening:

• Sensitivity of 84.6% across three screening rounds in the NELSON trial 2
• Specificity of 98.6% 2
• Negative predictive value of 99.8% 2
• Comparable image quality to standard diagnostic CT for nodule detection 4

Radiation Dose Comparison

The radiation dose difference between low-dose screening CT and standard diagnostic CT is substantial:

• Low-dose CT screening: 1.3-3.4 mSv 4
• Standard diagnostic CT: 8.5-14.0 mSv 4

Common Pitfalls to Avoid

1. Misinterpreting screening guidelines: Some clinicians incorrectly assume contrast is needed for better visualization, but this contradicts established protocols 1

2. Ordering diagnostic CT instead of screening CT: Ensure the correct low-dose non-contrast protocol is ordered specifically for screening purposes

3. False positives: Be aware that approximately 24.2% of low-dose CT screens may be positive, with over 95% of these not associated with lung cancer 3

4. Inappropriate patient selection: Screening should be limited to appropriate high-risk individuals who meet established criteria to maximize benefit and minimize harm 1

5. Inadequate follow-up planning: Structured reporting systems like Lung-RADS should be used to standardize nodule evaluation and follow-up recommendations 1

By adhering to these established protocols for non-contrast low-dose CT screening, clinicians can effectively balance the benefits of early lung cancer detection with the need to minimize radiation exposure and other potential harms.