Room: Exhibit Hall | Forum 2
Purpose: To quantify the accuracy of electron density (ED), effective atomic number (Zeff), iodine concentration derived from dual-layer CT and the material attribution feasibility based on ED and Zeff.
Methods: Measurements with tissue surrogate phantoms were performed on a dual-layer CT system (Philips IQon Spectral CT) installed in a radiation oncology department. ED was derived from the two-base model of photoelectric-like and Compton-scatter-like components. Ratio of two mono-energy attenuations was used to estimate the Zeff. Iodine concentration was derived by performing two basis decomposition (iodine and water). Scan parameters were varied to assess the impacts on accuracy. Material separation feasibility was evaluated on 2D scatter plots of ED vs. Zeff.
Results: The median deviations of ED from expected values of various tissue surrogates ranged from -0.1% to 1.1% at the standard condition (120kVp, 20mGy CTDIvol, 16x0.6125 mm collimation, 0.33-sec rotation). The median deviations of Zeff ranged from -2.3% to 1.7% for soft tissue and bone surrogates and was 6-7% for lung surrogates. Changes in tube potential (120 vs. 140 kVp), radiation dose (20 vs. 30 mGy), gantry rotation time (0.33 vs. 0.75 seconds), and spectral reconstruction level (0 vs. 3) resulted in absolute differences of <0.9% of water ED and <0.2 a.u. for Zeff when compared to results of the standard condition. All tissue surrogates were well separated on the ED-Zeff scatter plot, even for various soft tissues (adipose, brain, breast, and liver) that were clustered near water. For iodine concentration of 2â€“20 mg/mL, the median absolute deviations from the nominal values were <0.3 mg/mL.
Conclusion: Phantom measurements showed encouraging results which could lay a foundation for applications of dual-layer CT in radiation therapy, including direct import of ED and proton stopping power ratio images for treatment planning and quantitative iodine concentration map for tumor delineation and response assessment.
Funding Support, Disclosures, and Conflict of Interest: The presenting author has a research agreement with Philips Healthcare.