Date(s) - 03/15/2012
1:00 pm - 3:00 pm
Authors: Amy Geyer, Shannon O’Reilly, Choonsik Lee, Danny Long, Wesley Bolch
According to Report No. 160 by the National Council on Radiation Protection (NCRP), the effective dose per individual in the US due to medical exposures has risen nearly six-fold since 1982. Changes in the frequency of medical exposures and the types of modalities used are largely responsible for this large increase and it is now crucial to estimate organs doses to patients for diagnostic medical imaging and radiotherapy procedures. To assist in the rapid reporting of patient organ doses, researchers at the University of Florida and the National Cancer Institute have developed a family of computational hybrid phantoms, constructed from NURBS and polygon mesh surfaces, that fully represent the ICRP 89 reference newborn, 1-year-old, 5-year-old, 10-year-old, 15-year-old male and female, and adult male and female. Coupled with Monte Carlo simulations, these phantoms can be used to estimate patient organ doses. In a study performed by Johnson et al [Proceedings of the IEEE, vol. 97, No. 12, pp. 2060-2075], data from the CDC’s National Center for Health Statistics from 1988 to 1994 were used to create a library of phantoms extending through the 10th to 90th height/weight distributions. These phantoms were created, using modeling software, by scaling the UF/NCI reference phantoms to match targeted values of standing height, sitting height, total body weight, and secondary circumferential values. In total, Johnson et al created 25 adult male and 25 pediatric female patient-dependent phantoms. While suitable for initial studies for patient-phantom matching, substantial increases seen in childhood obesity over the intervening years has prompted us to undergo a major revision to the UF/NCI phantom library. Furthermore, a decision was made to construct the new library in a gridded fashion by height/weight without further reference to time-period-fixed weight/height percentiles. At each height/weight combination, secondary parameters of arm, thigh, waist, and buttock circumference are also defined and used for phantom construction. All morphometric data for the new library are taken from the CDC NHANES survey data over the time period 1999 to 2006, the most recent reported survey period. A subset of the phantom library was then used in a CT organ dose sensitivity study to examine the degree to which full Monte Carlo simulations would be required to track organ doses for patients that are severely underweight to obese in body size. Through data analysis, it was found that organ dosimetry can be established through data interpolation of a more coarsely defined voxelized phantom library subset. In the future, the UF/NCI phantom library will be used to construct pre-computed dose libraries for individuals undergoing CT examinations. Ultimately, these libraries can be deployed in the clinic for electronic recording of patient organ dosimetry following diagnostic imaging procedures.
Research supported by Contracts HHS-N2612-0090-0098P and HHS-N2612-0100-0692P with the Radiation Epidemiology Branch of the National Cancer Institute, and Grant from the Biomedical Research and Education Fund.