Sabrina Viviane Vollmar PhD, Abstract Co-Author: Nothing to Disclose

Daniel Kolditz PhD, Presenter: Employee, CT Imaging GmbH

Martin Hupfer PhD, Abstract Co-Author: Employee, CT Imaging GmbH

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

To evaluate potential dose contributions by scattered radiation to organs and tissues not directly exposed and the resulting effective dose in dedicated breast CT.

Calculation of dose in the directly and not directly exposed parts of the body were performed for dedicated breast CT at tube voltages of 40, 60 and 80 kV with a Monte Carlo (MC) software tool (ImpactMC, CT Imaging GmbH, Erlangen, Germany). Effective dose was calculated according to the ICRP publication 103. We used the standard female ORNL (Oak Ridge National Laboratory) phantom to mimic the patient lying prone on the examination table and added cylindrical phantoms with 10 and 14 cm diameter, and 7.5 and 10.5 cm in length, respectively to mimic the pendant breast. Only the examined breast was directly exposed. The air kerma of the scans was adapted to achieve an average glandular dose (AGD) of 1.6 and 4.6 mGy, respectively, for the two breast sizes, which corresponds to the dose limits in mammography in the European Guidelines for screening mammography.

Effective dose was confirmed at 0.192 mSv and 0.552 mSv for 10 and 14 cm breast sizes, respectively, for all tube voltages without scattered radiation. When taking scattered radiation into account effective dose increased to 0.200 and 0.601 mSv, respectively, for 60 kV. These values were reduced to 0.197 and 0.591 mSv when adding an absorption foil (150 µm Pb) to the examination table. Respective values were 0.196 and 0.570 mGy for 40 kV and 0.202 and 0.608 mGy for 80 kV. For the not directly exposed tissues highest organ dose values were found in the lung amounting to 0.029 and, 0.146 mGy, respectively. Adding the absorption layer to the table reduced these values to 0.026 and 0.128 mGy, respectively.

Effective dose in dedicated breast CT for a bilateral examination with typical values of 0.2 to 0.6 mSv is low; scattered radiation only contributes 2-3%, 3-7% and, 5-9% additional dose to these values for 40, 60 and 80 kV, respectively.

Dedicated breast CT potentially offers higher sensitivity and specificity for breast cancer detection without increasing dose levels significantly.

Vollmar, S, Kolditz, D, Hupfer, M, Kalender, W, Dose to Organs and Tissues from Scattered Radiation in Breast CT: Impact on Effective Dose.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14003964.html