Image quality benchmark test of a novel all-in-one integrated CT-Linac system

Image quality is essential for image-guided radiation therapy (IGRT) and may support potential adaptive radiotherapy (ART)-related applications. This study aims to establish a reproducible benchmarking methodology for image quality assurance (QA) and to evaluate the image performance of a novel All-in-One integrated CT-Linac system under clinically implemented imaging protocols. The image quality of the CT-Linac system was evaluated and compared with that of a Philips Brilliance Big Bore CT scanner and a Varian Halcyon 2.0 CBCT system. Two imaging modes of the CT-Linac system were investigated: fan-beam CT planning (FBCTp) and IGRT modes. A Catphan 700 phantom was used for the image quality assessment under the default clinical imaging protocols of each system. An in-house software platform was developed for automated quantitative analysis. Quantitative metrics, including CT number accuracy, noise, uniformity, low-contrast detectability, high-contrast spatial resolution, and geometric accuracy, were evaluated according to American College of Radiology (ACR) guidelines. Four site-specific CT number to relative electron density (RED) conversion curves were established using a 062 M electron density phantom under FBCTp mode imaging protocols. The consistency and accuracy of density calibration were further evaluated through repeated scans of the same phantom using the corresponding site of IGRT imaging protocols. The CT-Linac system demonstrated low-contrast detectability comparable to the Philips CT system. Compared with the Halcyon 2.0 CBCT system, improved performance was observed across most clinical protocols, including low-dose conditions (average tube current < 70 mAs). Higher contrast-to-noise ratio (CNR) values were observed under the IGRT mode protocols, except for the LowDose protocols; however, these differences may be influenced by variations in dose-related parameters. The high-contrast spatial resolution of the FBCTp mode was comparable to that of the Philips CT, while the IGRT mode exhibited slightly lower values but remained higher than those of the Halcyon CBCT under the evaluated protocols. Most materials exhibited CT numbers within the recommended range, and strong linearity between CT number and attenuation coefficients was observed across all systems ( R = 0.9987–0.9996). The CT-Linac system also demonstrated comparable uniformity and geometric accuracy across protocols. For materials with densities slightly greater or less than 1.0 (e.g., bone and lung), larger deviations in calibrated density were observed. Except for the Head and SlowScan protocols, the deviation between calibrated and reference densities remained within 1% for all IGRT protocols. The integrated CT-Linac system showed favorable measured image quality characteristics under clinically implemented imaging protocols and may support its application in IGRT and ART workflows. The proposed benchmarking framework provides a reproducible framework for image quality assurance and provides a practical reference for protocol selection, optimization, and cross-platform or cross-center comparisons.