Saravanabavaan Suntharalingam, Presenter: Nothing to Disclose

Franz Ferdinand Stecker, Abstract Co-Author: Nothing to Disclose

Nika Guberina MD, Abstract Co-Author: Nothing to Disclose

Jens Matthias Theysohn MD, Abstract Co-Author: Nothing to Disclose

Michael Forsting MD, Abstract Co-Author: Nothing to Disclose

Adrian Stefan Ringelstein MD, Abstract Co-Author: Nothing to Disclose

Thomas W. Schlosser MD, Abstract Co-Author: Nothing to Disclose

Kai Nassenstein, Abstract Co-Author: Nothing to Disclose

To investigate, how much the effective dose (ED) varies between follow-up examinations performed on the same CT scanner.

The effective dose (ED) was estimated retrospectively for 50 patients suffering from cancer at three different times of CT examination. At each time, a CT scan of the chest (CH), of the liver without contrast enhancing (LI) and of the entire abdomen after contrast media application (AB) was performed using the same predefined CT protocol and the same CT scanner (Siemens Definition FLASH). For automated radiation dose reduction Care Dose 4D and Care KV (Siemens) were used. Data were assessed following recommendations of ICRP 103 using Radimetrics’ dose-monitoring-software eXposure™.

The mean ED for CH was 5.0 ± 1.9 mSv, for LI 4.9 ± 2.0 mSv, and for AB 7.6 ± 3.3 mSv. The mean differences of ED between follow-up examinations were 0.8 ± 1.1 mSv for CH, 0.6 ± 0.7 mSv for LI, and 1.2 ± 1.6 mSv for AB. The differences between ED of follow-up examinations showed a strong correlation to the differences in the tube current (CH: 12.5 ± 10.8 mAs, r = 0.85; LI: 10.4 ± 10.2 mAs, r = 0.78; AB 14.8 ± 18.2 mAs, r = 0.70). The differences between the ED of follow-up examinations showed only a weak correlation to the differences in the scan length (CH: 22.0 ± 20.4 mm, r = 0.03; LI: 14.2 ± 12.7 mm, r = 0.11; AB 21.4 ± 20.9 mm, r = 0.35). Even though in the vast majority of CT examination the tube voltages had not been changed between follow-up examinations, changes in the tube voltage in individual cases had major effect on ED.

A high variance of the effective dose exists between follow-up CT examinations, when using the same CT scanner and scan protocol. This variance is predominantly caused by differences in the tube current, which had been automatically determined by the dose reduction algorithm.

Improvements in the automated tube current modulation algorithm are necessary to reduce radiation dose in CT.

Suntharalingam, S, Stecker, F, Guberina, N, Theysohn, J, Forsting, M, Ringelstein, A, Schlosser, T, Nassenstein, K, Effective Dose in CT Examinations: How Much Is the Effective Dose Varying between Follow-up Examinations Performed on the Same CT Scanner?.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14012889.html