Technical Note: Exploring the limit for the conversion of energy-subtracted CT number to electron density for high-atomic-number materials

摘要

Purpose: For accurate tissue inhomogeneity correction in radiotherapy treatment planning, the authors had previously proposed a novel conversion of the energy-subtracted CT number to an electron density (AHU-pe conversion), which provides a single linear relationship between AHU and pe over a wide pe range. The purpose of this study is to address the limitations of the conversion method with respect to atomic number (Z) by elucidating the role of partial photon interactions in the AHU-pe conversion process. Methods: The authors performed numerical analyses of the AHU-pe conversion for 105 human body tissues, as listed in ICRU Report 46, and elementary substances with Z = 1-40. Total and partial attenuation coefficients for these materials were calculated using the XCOM photon cross section database. The effective x-ray energies used to calculate the attenuation were chosen to imitate a dual-source CT scanner operated at 80-140 kV/Sn under well-calibrated and poorly calibrated conditions.