Natalia Saltybaeva, Abstract Co-Author: Nothing to Disclose

Martin Hupfer PhD, Presenter: Employee, CT Imaging GmbH

Daniel Kolditz PhD, Abstract Co-Author: Employee, CT Imaging GmbH

Bernhard Schmidt PhD, Abstract Co-Author: Employee, Siemens AG

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Consultant, Bayer AG Founder, CT Imaging GmbH Scientific Advisor, CT Imaging GmbH CEO, CT Imaging GmbH

Tube current modulation (TCM) and automatic exposure control (AEC) are widely used in modern CT. The aim of this work was to include the effects of TCM and AEC in a software package for fast and easy organ and effective dose estimates.

Measurements were carried out for a SOMATOM Definition Flash scanner (Siemens AG, Forchheim, Germany); the manufacturer provided all necessary information on their CARE Dose4D TCM/AEC product. TCM and AEC curves were derived for anthropomorphic phantoms by generating complete CT projection data sets by means of ray-tracing and predicting the flux at the detector. For all phantoms and parameter combinations studied, Monte Carlo (MC) calculations w&w/o CARE Dose4D were performed to provide tabulated dose values. These tables were included in the software package ImpactDose (CT Imaging GmbH, Erlangen, Germany) which estimates organ and effective dose depending on patient size, scan region and scan protocol. It is based on pre-tabulated dose values calculated by means of MC calculations for the ORNL family of anthropomorphic phantoms. Validation measurements were performed using thermoluminescence dosimeters (TLDs) for each of three different anthropomorphic phantoms (Rando adult, 5-y.o. and 1-y.o. CIRS) w&w/o CARE Dose4D.

Measured dose values were compared to MC results on a chip-by-chip basis. The mean differences for all TLD chips were 5%, 7%, and 6% for the adult, the 5-year old, and the 1-year old phantom, respectively. This deviation is in the range of the uncertainty associated with TLD measurements and indicates that TCM/AEC were correctly implemented. The derived dose values w&w/o TCM/AEC allowed for assessment of their effect on dose for different patients without the need for measurements or repeated MC calculations.

Dose estimates based on tabulated MC-derived dose distributions can provide accurate information on the effect of TCM and AEC in clinical CT if information about their implementation is provided by the manufacturer.

The software package allows to obtain fast and accurate dose estimates when TCM/AEC is used and furthermore may serve as a learning tool.

Saltybaeva, N, Hupfer, M, Kolditz, D, Schmidt, B, Kalender, W, Fast and Easy Dose Estimates including Tube Current Modulation and Automatic Exposure Control.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13044458.html