Lowering the thyroid dose in screening examinations of the cervical spine

Abstract

The first objective of this study was to test the hypothesis that a lower-dose (14.1 mGy thyroid dose) protocol for helical computed tomography (CT) of the entire cervical spine demonstrates equivalent technical adequacy and diagnostic accuracy as the standard-dose protocol (26.0 mGy thyroid dose) used at our institution. The second objective was to estimate the excess thyroid cancer mortality for three cervical spine screening protocols. Eight patients underwent two helical CT acquisitions of the entire cervical spine (standard and lower dose); from these acquisitions, a database of 128 randomized images (64 standard dose and 64 lower dose) was constructed. Three radiologists evaluated each of the 128 images for technical adequacy and, if the image was technically adequate, diagnostic accuracy. Historical data of excess thyroid cancer mortality stratified by age and sex were used to estimate the impact of lowering the thyroid dose in cervical spine screening. Estimates used a linear extrapolation of mortality data. The lower-dose protocol for helical CT of the entire cervical spine demonstrates equivalent technical adequacy and diagnostic accuracy as the standard protocol. The excess thyroid cancer mortality is a function of patient age and sex; for 25-year-old men, the excess mortality per 100,000 patients is 96.7 (standard-dose CT), 52.4 (lower-dose CT), and 6.7 (radiographs alone, 1.8 mGy thyroid dose). The equivalent technical adequacy and diagnostic accuracy of a lower-dose protocol for helical CT of the entire cervical spine support its implementation in routine screening. The excess thyroid mortality emphasizes the need to maintain an open dialogue with our referring clinicians with respect to the mechanism of injury, clinical findings, and radiation risks.