Survey of conventional and spiral CT doses

Abstract

PURPOSE: To investigate the radiation dose for conventional computed tomography (CT)and spiral CT during different CT examinations at various hospitals and practices. MATERIALS AND METHODS: CT dose index with an active length of 15 cm was measured in 16 different types of CT scanners by using ionization chamber dosimetry. Twenty-six holders (one 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 various CT examinations. Weighted CT dose index and dose-length product were determined for each examination. RESULTS: For most examinations, the tube current time product was significantly higher for conventional CT than for spiral CT (.002 ≤ P ≤ .05). The ratio of section distance to section thickness for conventional CT was significantly lower than the pitch for spiral CT (.001 ≤ P ≤ .05). The weighted CT dose index and dose-length product for spiral CT were about half of those for conventional CT. The third quartiles for weighted CT dose index and dose-length product for spiral CT were much lower than those recommended as reference doses. CONCLUSION: CT examinations with conventional CT scanners are often performed with unnecessarily high radiation dose. For the establishment of reference doses, the radiation dose with spiral CT scanners should be taken into account.