Low-Dose Computed Tomography Protocol
For lung cancer screening, perform LDCT using 120 kVp at 20-40 mA with 1.25 mm slice thickness, obtaining contiguous slices from thoracic inlet to adrenal glands in a single breath-hold without contrast material. 1
Technical Parameters for Lung Screening
Scanner Settings
- Multi-slice helical CT scanner is preferred over single-slice scanners for higher resolution images 1
- Tube voltage: 120 kVp (standard for all patients) 1
- Tube current: 20-40 mA depending on manufacturer:
- Slice thickness: 1.25 mm (GE) or 1 mm (Siemens) 1
- Rotation time: 0.5 seconds 1
Image Acquisition
- Coverage: Thoracic inlet to adrenal glands in contiguous slices 1
- Breath-hold: Single breath-hold acquisition (two breath-holds acceptable for single-slice scanners) 1
- Contrast: No intravenous contrast material 1
- Radiation dose: Target ≤3 mGy for most patients 1
Reconstruction and Display Parameters
Slice Thickness for Interpretation
- Preferred: ≤1.0 mm slice width for optimal nodule detection and measurement 1
- Acceptable: ≤2.5 mm slice width 1
- Critical caveat: Nonsolid lesions must be evaluated at thin slices (<1.5 mm) to exclude solid components, as part-solid nodules have higher malignancy rates 1
Window Settings for Nodule Assessment
- Lung window: Width 1500, Level -650 1
- Mediastinal window: Width 350, Level 25 1
- Display: High-resolution monitor with maximal magnification, scrolling through images individually 1
Radiation Dose Considerations
The median radiation dose with low-dose protocols is approximately 22% of standard-dose CT without compromising diagnostic accuracy. 1
- Target effective dose: ≤3 mGy for screening examinations 1
- Dose tracking: Use CT dose index and dose-length product monitoring to ensure adherence to low-dose limits 1
- Patient size adjustments: Same technical parameters should be maintained across all screening examinations for consistent nodule measurement 1
Protocol Variations by Clinical Application
Whole Body Low-Dose CT
- Coverage: Skull vertex to knees without contrast 2
- Radiation dose: 3.2-4.8 mSv (compared to 8-16 mSv for standard abdominal/pelvic CT) 2
- Slice thickness: ≤2.5 mm (with <1 mm preferred) 2
- Weight-based adjustments: 100 kVp for non-obese patients provides 30% dose reduction; higher kVp may be necessary for obese patients 2
Suspected Appendicitis
- Low-dose CT reduces radiation to 22% of standard-dose with no significant difference in negative appendectomy rates 1
- Contrast: Oral or rectal contrast may not be needed depending on institutional preference 1
Quality Assurance Requirements
Technical Standards
- Scanner accreditation: Must meet or exceed American College of Radiology quality standards 1
- Technologist training: All technicians performing LDCT must be trained in the specific low-dose protocol 1
- Annual protocol review: Dedicated LDCT protocols should be reviewed annually by supervising radiologists, medical physicists, and radiology technologists 2
Image Quality Verification
- Pre-dismissal review: CT data sets should be reviewed by trained personnel before patient dismissal to ensure complete imaging and adequate visualization 2
- Consistency check: Use training sets of screening LDCTs to ensure consistent application of reporting systems across radiologists 1
Common Pitfalls to Avoid
- Inconsistent technical parameters: Using different slice thickness, reconstruction algorithms, or window settings between serial scans will affect nodule size measurement accuracy 1
- Single-slice scanner limitations: When using single-slice scanners with collimation ≥5 mm, positive results are only tentative and require high-resolution CT confirmation 1
- Inadequate slice thickness for subsolid nodules: Failing to use <1.5 mm slices for nonsolid lesions may miss solid components in part-solid nodules 1
- Excessive dose in larger patients: While maintaining diagnostic quality is important, avoid reverting to standard-dose protocols without attempting weight-based low-dose adjustments first 2