PURPOSE: Determination of the influence of tube currents varying during a CT scan on organ doses and on the effective dose as a function of patient constitution. Evaluation of the accuracy of effective dose calculations based on summarizing parameters (effective mAs, dose length product [DLP]) compared to calculations based on slice-specific tube currents.

MATERIALS AND METHODS: Investigation of the CT datasets of 806 patients acquired from the skull base to the proximal thigh with respect to the body mass index (BMI). The effective dose was calculated by means of slice-specific as well as region-specific conversion factors.

RESULTS: Dose optimization by means of variable tube current resulted in a reduction of the gonad dose in patients with BMI < or = 20 ... 21 kg/m (2) and of the effective dose in patients with BMI < or = 26 kg/m (2). Effective dose values calculated with the DLP for 90 % of the patients are within an interval of +/- 20 % of the values calculated using slice-specific tube currents.

CONCLUSION: If tube current optimization during the CT scan was applied, for the scan region under investigation, at a BMI already below the German mean value, an increased effective dose was observed. Calculations of the effective dose on the basis of summarizing values such as DLP or effective mAs are of sufficient accuracy.