Jens Wiegert PhD, Presenter: Employee, Koninklijke Philips Electronics NV

Dianna M. Ehrhart Bardo MD, Abstract Co-Author: Speakers Bureau, Koninklijke Philips Electronics NV

Donna M. Stevens MS, Abstract Co-Author: Nothing to Disclose

Amar Dhanantwari, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Kevin M. Brown MS, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Jeffrey Harold Yanof PhD, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

To estimate CT organ dose from patient-specific, 3-D dose distribution maps (“dose maps”) and to determine the correlation of these estimates with an x-ray attenuation-based measure of patient size.

A Monte Carlo simulation technique was used to retrospectively compute color-coded dose distribution maps based on nine sequentially sampled image data sets from pediatric chest examinations (Philips, Ingenuity 64 channel CT). The patient ages ranged from 6 days to 15 yrs. and their weights ranged from 3.5-45 kg. The CT examinations included standard helical and axial scan protocols as well as default dose reduction strategies. The CTDIvol values ranged from 2.1 to 7 mGy. The MC simulations modeled the CT acquisition techniques including critical aspects of the image chain such as acquisition angle, beam filters, collimation settings, and bowtie filter. ROI’s were placed on the dose maps to estimate organ dose to lung and breast tissue. The water phantom equivalent diameter (WEP) was determined from the projection Surview. An exponential regression model was computed with organ dose (normalized to CTDIvol) and WEP diameter as the dependent and independent variables, respectively.   .

Colorized 3-D dose distribution maps were generated and reviewed for the chest examinations. The mean (+/- standard deviation) values for lung and breast tissue were 1.65 +/- 1.0 mGy and 1.8+/- 0.9 mGy respectively. The exponential regression model of organ dose (normalize to CTDI) and WEP had an R2 value of 0.71, with an average WEP diameter of 16.1+/- 5.6 cm.  

Preliminary results indicate that patient-specific dose maps can be computed from MDCT data sets. Organ dose estimated from dose maps is correlated with the patient’s water phantom equivalent diameter.

Visualization of patient-specific dose maps and reporting of absorbed dose to radiosensitive organs can lead to more optimal dose management in this population.

Wiegert, J, Bardo, D, Stevens, D, Dhanantwari, A, Brown, K, Yanof, J, Organ Dose with Pediatric Chest CT: Estimation from Patient-specific Dose Distribution Maps and Correlation with a Measure of Patient Size.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034243.html