Mark Patrick Supanich PhD, Presenter: Research Grant, Siemens AG

Donald Peck PhD, Abstract Co-Author: Nothing to Disclose

This work aims to validate the use of a Size-Specific Dose Estimate (SSDE), as proposed by AAPM TG Report 204, as an indicator of absorbed organ doses. This research examines the use of SSDE as a metric in the specific case of Abdomen and Pelvis Computed Tomography (CT) studies using Automatic Exposure Control (AEC).

Under IRB approval, retrospective organ dose estimates from CT Abdomen and Pelvis studies using AEC on two volumetric CT scanners from two different manufacturers were carried out using a commercially available program, eXposureTM. The software used two phantom models from the Cristy set of models to complete the Monte Carlo simulation to estimate organ doses based on the area scanned and the scanner output. Mean organ dose of the liver, stomach, kidney, gall bladder, pancreas and spleen were calculated as well as the SSDE for the acquisition using the AAPM TG 204 conversion factors and the scanner reported CTDIvol. The conversion factor for each study was determined by the software by thresholding the midscan image and determining the effective diameter of a circle of equivalent area to the patient at the midscan point. Data from a total of 328 studies over a period of 4 months were identified for analysis with effective diameters within +/- 2 cm of the phantom model effective diameters (25.5 and 28.3 cm).

A linear relationship was found between SSDE and mean absorbed organ dose with a slope of 1.05 and a Pearson Correlation Coefficient of 0.97. The exams analyzed had calculated effective diameters from 23.5 cm to 30.3 cm and SSDE values ranged from 10 to 32 mGy. The linear relationship between SSDE and calculated mean organ dose was observed to deteriorate as the absolute difference of the calculated effective diameter and the phantom model effective diameter increased.

The validity of the use of SSDE as an indicator for absorbed organ dose in Abdomen and Pelvis studies is confirmed by the retrospective Monte Carlo simulation of absorbed organ doses and calculation of effective diameter in clinical CT studies.

A Size-Specific Dose Estimate offers a patient-specific, estimate of absorbed organ doses for clinical CT studies of the Abdomen and Pelvis in the absence of access to Monte Carlo simulation software.

Supanich, M, Peck, D, Size-Specific Dose Estimate as an Indicator of Absorbed Organ Dose in CT Abdomen and Pelvis Studies.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12023193.html