Room: Exhibit Hall | Forum 8
Purpose: For Monte Carlo dose calculation in heterogeneous media, effective atomic number (Zeff) derived from dual-energy CT images can be used for tissue segmentation. In previous studies, Landry (Phys. Med. Biol., 58, 6851 (2013)) and Saito (Med. Phys., 44, 2293 (2017)) performed Zeff calibration on Gammex RMI 467 and CIRS 002H5 phantoms. For the CIRS phantom, four and five different rods were used in Landry's and Saito's study, respectively. In this work, we extended the same measurements to 13 CIRS rods (Model 062M) to include materials such as lung (inhale) and lung (exhale) and present our Zeff calibration results.
Methods: 13 material rods of the CIRS 062M phantom were scanned on a GE RT590 CT machine using both 80 and 140 kVp x-ray beam energies. In-house Matlab codes following the methodologies of Saito and Landry were written and validated using their published data. Calibration curve of Zeff vs. HU was obtained from scanning CT images of the 13 different materials by applying the in-house Matlab codes.
Results: Significant differences [lung (inhale): 35.0% and lung (exhale): 17.1%] were discovered between derived Zeff and fitted calibration curve following Saito's method for low density materials. Similar large deviation (13.5%) was found for lung (inhale) but not for lung (exhale) (1.2%) according to Landry's method. Our analysis also showed good fitting results for all other rod materials.
Conclusion: Significant calibration differences for low density materials were found when obtaining Zeff following both the Saito's and the Landry's method using the popular CIRS 062M phantom. Reasons for the differences are not clear. Further investigation is necessary to confirm the finding.