Survey of conventional and spiral CT doses

PURPOSE: To investigate the radiation dose for conventional computed tomogr aphy (CT) and spiral CT during different CT examinations at various hospita ls and practices. MATERIALS AND METHODS: CT dose index with an active length of 15 cm was mea sured in 16 different types of CT scanners by using ionization chamber dosi metry. Twenty-six holders tone who has legal responsibility under national law for a radiologic installation) operating a total of seven conventional and 20 spiral CT scanners were asked for their standard parameters for vari ous CT examinations. Weighted CT dose index and dose-length product were de termined for each examination. RESULTS: For most examinations, the tube current time product was significa ntly higher for conventional CT than for spiral CT (.002 less than or equal to P less than or equal to .05). The ratio of section distance to section thickness for conventional CT was significantly lower than the pitch for sp iral CT(.001 less than or equal to P less than or equal to .05). The weight ed CT dose index and dose-length product for spiral CT were about half of t hose for conventional CT. The third quartiles for weighted CT dose index an d dose-length product for spiral CT were much lower than those recommended as reference doses. CONCLUSION: CT examinations with conventional CT scanners are often perform ed with unnecessarily high radiation dose. For the establishment of referen ce doses, the radiation dose with spiral CT scanners should be taken into a ccount.