Kyle McMillan, Presenter: Institutional research agreement, Siemens AG Research support, Siemens AG

Maryam Bostani PhD, Abstract Co-Author: Research support, Siemens AG

Cynthia H. McCollough PhD, Abstract Co-Author: Research Grant, Siemens AG

Michael F. McNitt-Gray PhD, Abstract Co-Author: Institutional research agreement, Siemens AG Research support, Siemens AG

To demonstrate the feasibility of estimating organ doses for patients undergoing tube current modulated (TCM) CT exams using a combination of: (a) a patient size metric derived from existing data in the CT localizer radiographs and (b) a scanner output metric based on the anatomical region of interest (CTDIvol-regional).

For 20 patients who underwent clinically indicated TCM exams of the chest (n=10) or abdomen/pelvis (n=10), the CT localizer radiograph, image data and TCM data were obtained. The CT localizer radiograph (topogram) generated from most Siemens CT scanners contains a private DICOM field that stores an array of numbers describing AP and LAT attenuation-based measures of patient dimension. The square root of the product of the AP and LAT size data was used to calculate an estimate of water-equivalent diameter (WED-topo). For comparison, the image data was also used to calculate water-equivalent diameter (WED-image). Using a previously published approach, the average effective mAs over the anatomical region of interest was used to generate a regional descriptor of scanner output (CTDIvol-regional). Using previously described correlations between WED and organ doses normalized by CTDIvol-regional, estimates of organ dose (OD) were obtained using WED-topo and WED-image over the anatomical region of interest for the lung (chest scans) and liver (abd/pel scans). These estimated organ doses were then compared to estimates obtained with detailed Monte Carlo (MC) simulations that modeled individual patient anatomy and TCM data.

For abdomen/pelvis scans, the average difference between MC liver dose and OD(WED-image) and OD(WED-topo) was 6.06% and 7.43%, respectively. For chest scans, the average difference between MC lung dose and OD(WED-image) and OD(WED-topo) was 11.10% and 12.93%, respectively.

For both abdomen/pelvis and chest TCM CT examinations, organ dose estimated using WED derived from data in the DICOM header of the topogram was comparable to organ dose estimated using WED derived from image data. The topogram-based method has the advantage that WED data are readily available without additional post-processing of the image data.

Accurate estimates of dose to patients undergoing TCM CT examinations can be obtained based on size data already available in some CT scan radiographs and a regional measure of scanner output.

McMillan, K, Bostani, M, McCollough, C, McNitt-Gray, M, Estimating Organ Dose from Tube Current Modulated CT Exams Using Size Data Available in the DICOM Header of CT Localizer Radiographs and Regional Scanner Output.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011036.html