Dana M. Jackson RT, Presenter: Nothing to Disclose

Jacqui Hislop-Jambrich PhD, Abstract Co-Author: Employee, Toshiba Corporation

For SSDE to be an accurate and robust method for estimating individual patient dose, patients must be positioned at isocentre.

Cardiac CTA (CCTA) utilization has increased steadily, and as such is contributing to an increasing medical ionizing radiation burden. The dose received by individuals however is affected by multiple factors including the unintended effects on dose modulation caused by operator mal-positioning. The AAPM has developed size specific dose estimates (SSDE) to use an individual’s size to more accurately estimate the dose delivered during a CT. The purpose of this research is to determine if significant differences exist between all SSDE's from cardiac CTA's using the dose metrics displayed by the scanner and corrected dose metrics accounting for improper positioning within the gantry.  

A total of 94% of patients were positioned greater than 1cm from isocentre resulting in significant dose increases for 75% of patients. Without applying corrections for mal-positioning, significant variations in SSDEs for the different calculation methods was apparent. In some instances the variation was in the order of 50%. Greatest variations occurred when comparing the SSDE calculated from the AP diameter and the lateral diameter in obese patients. Once corrections for mal-positioning were applied to the data, the majority of cases resulted in similar SSDEs for all calculation methods.

Under ethics approval 100 consecutive females undergoing routine CCTA were retrospectively evaluated. Using data obtained from anthropomorphic phantom studies, we determined the effects of mal-positioning within the gantry on dose and size assessments. Corrections were made to the dose and size metrics for all 100 patients.

Jackson, D, Hislop-Jambrich, J, SSDE and Isocentre - A Weighty Relationship.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14016127.html