SU‐E‐I‐99: Estimation of Effective Charge Distribution by Dual‐Energy CT Reconstruction

Abstract

Purpose:Computed Tomography (CT) is a method to produce slice image of specific volume from the scanned x‐ray projection images. The contrast of CT image is correlated with the attenuation coefficients of the x‐ray in the object. The attenuation coefficient is strongly dependent on the x‐ray energy and the effective charge of the material. The purpose of this presentation is to show the effective charge distribution predicted by CT images reconstructed with kilovoltage(kV) and megavoltage(MV) x‐ray energy.Methods:The attenuation coefficients of x‐ray can be characterized by cross section of photoionization and Compton scattering for the specific xray energy. In particular, the photoionization cross section is strongly correlated with the effective charge of the object. Hence we can calculate effective charge by solving the coupled equation between the attenuation coefficient and the theoretical cross section. For this study, we use the megavoltage (MV) and kilovoltage (kV) x‐rays of Elekta Synergy as the dual source x‐ray, and CT image of the Phantom Laboratory CatPhan is reconstructed by the filtered back projection (FBP) and iterative algorithm for cone‐beam CT (CBCT).Results:We report attenuation coefficients of each component of the CatPhan specified by each x‐ray source. Also the effective charge distribution is evaluated by the MV and kV dual x‐ray sources. The predicted effective charges are comparable with the nominal ones.Conclusion:We developed the MV and kV dual‐source CBCT reconstruction to yield the effective charge distribution. For more accuracy, it is critical to remove an effect of the scattering photon in the CBCT reconstruction algorithm. The finding will be fine reference of the effective charge of tissue and lead to the more realistic absorbed‐dose calculation.This work was partly supported by the JSPS Core‐to‐Core Program(No. 23003), and this work was partly supported by JSPS KAKENHI 24234567.