Elliott James Stepusin MS, Presenter: Nothing to Disclose

Daniel J. Long PhD, Abstract Co-Author: Nothing to Disclose

Wesley E. Bolch PhD, Abstract Co-Author: Nothing to Disclose

In recent years, states and health care organizations have required the reporting of computed tomography (CT) exposure reports for all patients. These requirements coupled with national attention on radiation exposure have created a need for accurate and accessible computed tomography dosimetry. This work shows a computational method for creating exam-specific organ dose and effective dose coefficients that can account for tube current modulation (TCM).

Organ dose estimates (mGy per average-effective-mAs) were calculated for the ICRP 89 reference computational phantoms for common CT torso exams using a Monte Carlo transport code modeling a Toshiba 64-slice scanner. Local attenuation values within each phantom were the basis for accounting for TCM during the organ dose calculations. Effective dose coefficients (µSv•mGy-1•cm-1) were calculated using CTDIvol and exam length data with each phantom’s weighted organ doses. These values were compared to effective dose estimates derived from physical measurements (using OSL dosimeters) inside anthropomorphic phantoms representing the ICRP 89 reference 10-year-old hermaphrodite, 15-year-old female, and adult male phantoms.

Effective dose was estimated using an adult reference effective dose coefficient and the scanner reported DLP, using an adult reference effective dose coefficient and the SSDE weighted scanner reported DLP, using the phantom-specific effective dose coefficient and the scanner reported DLP, and using the phantom-specific organ dose values and the image-based average effective mAs. The average magnitude in percent error when comparing measured and calculated effective dose across all phantoms and energies for the four methods were 23.0 ± 15.8%, 14.6 ± 7.1%, 12.5 ± 4.4%, and 6.4 ± 3.7%, respectively.

This work shows the potential for predicting patient organ dose and effective dose values that account for TCM. Image based average effective mAs shows increased accuracy over scanner reported DLP as a means for patient-specific organ dosimetry.

This work can be expanded to provide patient-specific organ dose and effective dose estimates that can account for tube current modulation across a variety of scanner makes and models.

Stepusin, E, Long, D, Bolch, W, Monte Carlo Based Organ Dose and Effective Dose Coefficients for Common Computed Tomography Torso Examinations on the ICRP 89 Reference Phantoms that Account for Tube Current Modulation.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14016511.html