Measuring the impact of using 3D helical scout scans on overscan and radiation exposure

Scout scans in CT imaging guide scan range selection but are limited by restricted exposure angles and poor anatomical visibility, potentially increasing patient dose or missing vital anatomy. Low-dose 3D helical scout scans offer improved anatomical detail for range determination, yet their impact on overscan and radiation dose remains underexplored. This study investigates differences in overscan and effective dose between 2D and 3D helical scout scans to determine statistical significance.

This retrospective audit was conducted at a centre with two CT scanners from the same manufacturer-one supporting 3D helical scout scans, the other limited to 2D scouts. Overscan was measured for CT Abdomen Pelvis and CT Calcium Score examinations. Dose metrics (DLP and CTDI_vol) were extracted from Radiation Structured Dose Reports, and differences in effective dose were calculated using k-factors.

No statistically significant difference in overscan was found for CT Calcium Score examinations (n = 214), suggesting 2D scouts are sufficient for planning these scans. In contrast, CT Abdomen Pelvis examinations (n = 118) showed a significant 9.2 mm reduction in total overscan when using the 3D helical scout, corresponding to a dose reduction of 0.2 mSv.

3D helical scout scans do not significantly reduce overscan for CT Calcium Score examinations but do significantly reduce overscan and overall exam time for CT Abdomen Pelvis examinations. Their use in other examinations and impact on workflow-beyond the limited measurement of irradiation time-should be explored further, including effects on planning, positioning, and reporting times.