What is the recommended protocol for a whole body low dose Computed Tomography (CT) scan?

Whole Body Low Dose CT Protocol Recommendations

The recommended protocol for whole body low dose CT (WB-LDCT) should extend from skull vertex to knees (without intravenous iodinated contrast), with radiation doses between 3.2-4.8 mSv to maintain diagnostic accuracy while minimizing radiation exposure. 1

Technical Parameters

• WB-LDCT should be performed on multidetector CT scanners with 4 or more detectors to ensure better colonic distention and fewer respiratory artifacts 1
• Slice thickness should be ≤2.5 mm (with <1 mm preferred) to maintain adequate diagnostic quality while balancing radiation dose and image noise 1, 2
• kVp should be set at 120 kV with reduced tube current (mAs) adjusted according to patient size to minimize radiation exposure 1
• For average-sized patients, maintain CT dose volume index (CTDIvol) at ≤3.0 mGy, with appropriate adjustments for larger or smaller patients 2, 3
• Automatic exposure control should be utilized to vary the x-ray tube current over different body regions, resulting in significant dose savings for average-sized patients 1, 4

Weight-Based Protocol Adjustments

• Quality reference tube current, peak kilovoltage, and slice collimation should be adjusted according to patient weight 5
• Lower tube voltage settings (100 kVp) can be used for non-obese patients, providing up to 30% dose reduction without loss of diagnostic information 1
• For obese patients, higher kVp settings may be necessary to maintain adequate image quality 1, 5
• Weight-based protocols can achieve CTDI(vol) reductions of up to 13.9% and dose-length product (DLP) reductions of up to 16.1% compared to fixed protocols 5

Radiation Dose Considerations

• WB-LDCT protocols are associated with radiation doses of 3.2-4.8 mSv, significantly lower than conventional CT while maintaining diagnostic accuracy 1
• For comparison, the average annual background radiation exposure is approximately 3.1 mSv 1
• The effective dose for standard CT of the abdomen and pelvis ranges from 8-16 mSv, making WB-LDCT a significantly lower radiation alternative 1
• Dose reduction techniques should always be applied when possible, with the lowest dose used that maintains adequate diagnostic quality 1, 4

Clinical Applications

• WB-LDCT is recommended as first-line imaging for suspected solitary plasmacytoma (SP) or multiple myeloma (MM) according to European Myeloma Network guidelines 1
• The CT component of PET/CT studies should permit accurate assessment of the skeleton from vertex to knees and include the arms for optimal evaluation 1
• For colorectal cancer screening, low-dose CT colonography protocols should follow American College of Radiology guidelines with appropriate dose reduction techniques 1
• For suspected appendicitis, low-dose CT protocols can reduce radiation exposure to 22% of standard-dose protocols without compromising diagnostic accuracy 1

Quality Assurance Measures

• Programs should develop dedicated LDCT protocols reviewed annually by supervising radiologists, medical physicists, and radiology technologists 2
• Structured reporting systems should be used to standardize findings and recommendations 2
• CT data sets should be reviewed by trained technologists or physicians prior to patient dismissal to ensure complete imaging and adequate visualization 1
• Images should be sent to a dedicated CT workstation for interpretation and archived for future comparison 1

Common Pitfalls and Considerations

• Excessively low dose settings may compromise image quality, particularly in obese patients or areas with high attenuation 1, 3
• Submillimeter slice thicknesses increase image noise and radiation dose if noise is held constant, so they should be used judiciously 1
• Extracolonic findings, which are present in up to 16% of patients undergoing CT colonography, may require additional workup and should be reported appropriately 1
• For pediatric patients, more aggressive dose reduction protocols should be considered, with weight-based adjustments to both injected activity (for PET/CT) and CT parameters 6

By following these protocol recommendations, healthcare providers can achieve optimal diagnostic quality while minimizing radiation exposure to patients undergoing whole body low dose CT examinations.