How to estimate multislice CT effective dose more correctly.

The purpose of this paper is to provide data concerning differences in multislice CT effective dose estimation when using various methods and techniques, determine the reasons for these differences, and submit proposals for improving the estimation accuracy. All the experiments (chest and head exam settings) were conducted using 64-slice CT scanners from various manufacturers. Effective dose estimates have been obtained on the basis of the conventional dose-length product method, absorbed dose distribution curves, and using anthropomorphic phantoms with thermoluminescent dosimeters as a model method. Using the conventional dose-length product method leads to underestimation of effective doses (approximately 16 and 19% for head and chest studies, respectively, on average for all scanners) due to partly neglecting scattered in-patient radiation. Additional differences in dose estimates occur when using the "new" ICRP 103 instead of the "old" ICRP 60 Publication recommendations (13% for chest and 23% for head studies on average). It seems reasonable to calibrate scanners with weighted CT dose index values taking into account complete scattered radiation effects. Dose conversion factors for different studies and patient age must be recalculated in conformity with ICRP Publication 103 recommendations. With implementation of the presented proposals, the discrepancy in effective dose evaluation will not exceed a few percent as compared to anthropomorphic phantom measurements.