Author: Sorour Hosseini, YuHuei Jessica Huang, Thomas Boyd Martin, Geoffrey S. Nelson, Nicholas Pierre Nelson, Hui Zhao 👨🔬
Affiliation: University of Utah, Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah 🌍
Purpose: To evaluate image quality—including noise, contrast-to-noise ratio (CNR), uniformity, and low-contrast visibility (LCV)—on the HyperSight and TrueBeam cone-beam computed tomography (CBCT) platforms.
Methods: The CatPhan 604 phantom was used to assess image quality on a Halcyon equipped with HyperSight CBCT (HS-CBCT) and a TrueBeam using iterative CBCT (iCBCT) reconstruction (TB-CBCT). All HyperSight CBCTs utilized the iCBCT Acuros reconstruction method. Measurements were conducted with and without an annulus surrounding the CatPhan to simulate varying patient thicknesses. In addition to increasing the phantom thickness, the annulus also alters the cross-sectional shape of the phantom from a cylinder to an elliptical shape that resembles the abdominal region of a patient laying on the treatment couch. Image quality metrics were characterized as functions of exposure (mAs). Image noise and uniformity were assessed within the uniform region of the phantom, while CNR and LCV were derived from the material insert region. Both systems utilized 125 kV CBCT scans, with TrueBeam employing a 46.4 cm field of view (FOV) and HyperSight using 36 and 54 cm FOVs.
Results: Without the annulus, TB-CBCT exhibited lower noise and better LCV and uniformity compared to HS-CBCT. However, with the annulus, HS-CBCT demonstrated significant improvements in noise, CNR, uniformity, and LCV over TB-CBCT. For example, with the annulus, TB-CBCT noise ranged from 6.1% to 1.2% at 134-948 mAs, while HS-CBCT noise ranged from 3% to 1% at 131-964 mAs. The larger FOV on HyperSight provided slight improvements in image quality metrics at the expense of reduced spatial resolution relative to the smaller FOV.
Conclusion: Without the annulus, TrueBeam iCBCT and HyperSight delivered comparable image quality. When simulating increased patient thickness using the annulus, HyperSight CBCT outperformed TrueBeam CBCT across all metrics evaluated in this work.