Calculated organ doses and effective dosage for CT examination of the thorax and abdomen: Are these doses realistic?

Purpose: To analyse how far dose calculations for the CT examination of the thorax and abdomen can lead to faulty estimations of organ doses and effective dose due to differences in the topographic anatomy between mathematical phantom and man. Methods: For the CT examination of the thorax, upper abdomen, pancreas, pelvis and the entire abdomen, organ doses were calculated with conversion factors, first with regard to the topographic relation within the phantom, then with additional regard to the real anatomy of the man. Results: In the phantom, the abdomen lies outside the scan volume in case of CT-examination of the thorax and the whole intestine outside the scan volume in case of CT-examination of the upper abdomen and the pancreas, whereas the entire intestine is directly exposed in case of CT-examination of the pelvis. Dependent on whether dose calculations take real anatomy into account, doses of special organs can differ by a factor greater than 15. The calculated effective doses differ by a factor less than 1.5. Conclusions: Calculations of organ doses for the CT examination of the thorax and abdomen can lead to considerable errors due to different topographic relations between phantom and man. In contrast, the calculated effective dose is realistic. Hence, dose calculations with the help of mathematical phantom is an efficient method to estimate the total radiogenic risk.