Maryam Bostani PhD, Presenter: Research support, Siemens AG

Kyle McMillan, Abstract Co-Author: Institutional research agreement, Siemens AG Research support, Siemens AG

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

John J. Demarco PhD, Abstract Co-Author: Nothing to Disclose

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

The purpose of this work is to compare organ doses estimated using a validated CT Monte Carlo simulation package using MCNPX to those obtained using available dose estimation programs for chest and abdomen scans using Tube Current Modulation (TCM). 

Detailed tube current modulation (TCM) Monte Carlo simulations were performed using MCNPX based tools on 6 patient models (3 thoracic and 3 abdomen/pelvis scans), which were generated from actual patient images. Dose to fully irradiated organs (lung and breasts in thoracic scans and liver, spleen, and kidneys in abd/pel scans) were estimated. Patient models were selected to represent a spectrum of sizes, containing a model smaller and larger than the MIRD phantom used by the other dose estimation programs. Additionally, for all 6 patients, the Size Specific Dose Estimate (SSDE) was estimated based on each patients average water equivalent diameter (WED) over the scan region. . For comparison, organ doses and SSDE were obtained (where possible) from two available software packages that are also based on Monte Carlo simulations: the Radimetrics software (Bayer Healthcare) and ImPACT dose spreadsheet. For both ImPACT and Radimetrics, TCM is not modeled directly; therefore, an average tube current across the scan region was used. Estimated doses were compared across all three methods and all 6 patients using percent differences. 

The calculated SSDE based on WED agreed with Radimetrics estimated SSDE to within 4% for chest and to within 10% for abdomen scans. However, the organ doses had much higher differences. Across all 3 thoracic models the average percent differences for lung and breasts between Radimetrics and MC simulations were 32% and 42% and for ImPACT and MC simulations were only 11% and 15% respectively. Across the abd/pel models the average percent differences for liver, spleen, and kidneys between Radimetrics and detailed MC simulations were 26%, 34%, and 40% and for ImPACT and MC simulations were 19%, 15%, and 26%, respectively.  

Despite good agreement in SSDE values, the estimated organ doses by Radimetrics were much higher than those provided by the other two methods (ImPACT and detailed MC simulations). 

A comparison between different methods of estimating organ dose can help understand the existing error bars across dose estimates for further improvement of dose estimation methods.  

Bostani, M, McMillan, K, Cagnon, C, Demarco, J, McNitt-Gray, M, A Comparison of Organ Dose Estimates between Several Monte Carlo Simulation-based Methods for Chest and Abdomen CT Scans Using Tube Current Modulation (TCM).  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045534.html