Yulia Smal MSc, Presenter: Nothing to Disclose

Wei Chen MEng, Dipl Eng, Abstract Co-Author: Nothing to Disclose

Daniel Kolditz, Abstract Co-Author: Employee, Artemis Imaging GmbH

Cláudia Sá dos Reis MSc,RT, Abstract Co-Author: Nothing to Disclose

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

Effective dose (E) estimates for CT examinations are commonly based on the dose-length product (DLP) provided by the CT scanner multiplied by conversion factors (CF) specific for anatomic scan regions. In 2007 the new ICRP report 103 recommendations were published resulting in important changes in the field of radiation protection. Tissue weighting factors (Wt) were revised and new voxel phantoms were explicitly demanded to be used for dose evaluation. To our knowledge, there are no published data about CF considering the reference men models provided by ICRP report 110. The aim of this study was to reevaluate commonly used conversion factors in order to comply with recent recommendations regarding the new Wt and reference men models.

Organ dose and E values for the ICRP male and female reference voxel phantom were determined using an Monte Carlo dose calculations (ImpactMC, CT Imaging GmbH, Erlangen, Germany) for a SOMATOM Sensation 64 scanner (Siemens Healthcare, Forchheim, Germany). Five anatomical regions were considered corresponding to head, neck, chest, abdomen, and pelvis representing the regions typically defined for CF. All scan parameters were kept constant. The organ dose values were determined from the 3D dose distributions. The E values were computed using the organ Wt published in ICRP 60 and 103, respectively. From these data, new CF values were derived and compared to the previous AAPM and European Commission (EC) values.

The CF values we determined for head, neck, and pelvic regions were lower than the AAPM and EC values by 24 to 33 %, but higher for chest and abdomen regions by 30 to 57 %. The biggest difference among the genders was found for the pelvis with up to a factor of 3 for ICRP 60. This difference was smaller for ICRP 103 but still higher by a factor of about 2. The gender difference in the thorax is enhanced by the new ICRP data which gave higher weight to the female breast. E.g., coefficients of 0.0238 and 0.0202 should be considered for thorax CT of females and males, respectively, for ICRP 60 while CF values of 0.0277 and 0.0229 would apply for ICRP 103.

New conversion factors are indicated in view of ICRP report 103 and should be applied in clinical practice. The factors should take the gender into account.

The concept of using DLP-to-E conversion is considered very useful, but updating conversion factors is indicated.

Smal, Y, Chen, W, Kolditz, D, Reis, C, Kalender, W, Conversion of the Dose-Length Product into Effective Dose Taking Recent ICRP Recommendations into Account.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034470.html