Maryam Khatonabadi, Presenter: Nothing to Disclose

Adam Turner BS, Abstract Co-Author: Nothing to Disclose

Di Zhang MS, Abstract Co-Author: Nothing to Disclose

John Demarco, Abstract Co-Author: Nothing to Disclose

Christopher H. Cagnon PhD, Abstract Co-Author: Nothing to Disclose

Michael F. McNitt-Gray PhD, Abstract Co-Author: Institutional research agreement, Siemens AG Research grant, Siemens AG Instructor, Medical Technology Management Institute

For a fixed tube current scan the CTDIvol is constant across the entire scan region, but in tube current modulated (TCM) scans the CTDIvol changes depending on the scanned region. Therefore only the average CTDIvol over all regions is being reported. The purpose of this work was to compare simulated organ doses from tube current modulated scans with different CTDIvol values (including a region specific CTDIvol values) and to demonstrate the relationship between these CTDIvol values and organ dose for scans using TCM.

Using 40 abdomen/pelvis scans with TCM (Care Dose4D) acquired on a Siemens Sensation 64, voxelized models with contoured abdominal organs (liver, spleen and kidneys) were created. Using a Monte Carlo based simulation package dose to these organs were estimated. Simulated organ doses were compared with three CTDIvol values: CTDIvol reported on the scanner (CTDIvol,Abd/Pel), CTDIvol based on average effective mAs of only abdomen region of the scan (CTDIvol,Abd), and CTDIvol based on average effective mAs from images containing only the organ (e.g. CTDIvol,Liver). To investigate the relationship between organ dose and different CTDIvol values, organ doses were normalized by each CTDIvol value and plotted versus patient perimeter. These results were also compared to recent publications demonstrating the relationship between CTDIvol and organ dose for fixed tube current scans.

This study demonstrated that average CTDIvol value based on an entire TCM scan underestimates organ dose by up to 33%. This percentage increased to 43% and 38% for CTDIvol,Abd and CTDIvol,Liver, respectively. However, organ doses normalized by CTDIvol,Abd and CTDIvol, Liver showed a strong linear correlation with patient perimeter compared to organ doses normalized to scanner reported CTDIvol. Similar linear correlation was observed for fixed tube current results.

Overall CTDIvol underestimates organ dose up to 50%. However, specific region-CTDIvol-normalized organ doses showed strong correlation with patient size and therefore can be used to estimate organ doses from a TCM scan using patient perimeter and region specific CTDIvol.

This study introduces the feasibility of region specific CTDIvol to estimate organ dose from TCM by establishing a linear relationship between CTDIvol-normalized organ dose and patient perimeter.

Khatonabadi, M, Turner, A, Zhang, D, Demarco, J, Cagnon, C, McNitt-Gray, M, Linear Relationship between Organ Specific CTDIvol-Normalized Organ Dose and Patient Perimeter for Tube Current-modulated CT Scans.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11008412.html