Image Quality Characterization of on-Board Kilovoltage-CBCT Systems on Modern Linear Accelerator Units
Abstract
Purpose
To quantitatively evaluate and compare imaging performance of various kV-CBCT systems implemented on modern C-arm and O-ring linear accelerator units.
Methods
Imaging systems evaluated include separate C-arm units with an original 40x30cm2 panel (C-4030) and an updated 43x43cm2 panel (C-4343) and an O-ring unit with an updated 86x43cm2 panel (O-8643). The O-8643 system was assessed in both IGRT and planning (CBCTp) modes. The image quality phantom was scanned across all default acquisition modes available on each system, and images were reconstructed using both standard and iterative (iCBCT) algorithms. Image quality metrics including noise, uniformity, low-contrast visibility (LCV), spatial resolution, and CT number linearity were evaluated via Python scripting developed with the Pylinac library.
Results
Noise levels were lowest for O-8643 CBCTp mode, while comparable noise levels were observed for O-8643 IGRT, C-4343, and C-4030. Iterative reconstruction noticeably reduced noise compared to standard reconstruction for all systems. Uniformity was best for O-8643 (both modes), though C-4343 demonstrated a slight improvement in uniformity overall compared to C-4030. Mild "cupping" artifact was generally present across the various acquisitions on each system. LCV was best for O-8643 CBCTp, while C-4343 offered improved LCV compared to O-8643 IGRT and C-4030. The C-4343 and C-4030 systems exhibited a modest improvement in spatial resolution compared to O-8643, while for each system standard reconstruction yielded superior spatial resolution compared to iCBCT. CT number linearity was comparable across all platforms. Acquisition times were as short as 6s for O-8643, compared with 23-40s for C-4343 and approximately 33-60s for C-4030.
Conclusion
The O-8643 system, particularly in CBCTp mode, demonstrated modestly improved image quality overall relative to C-4343, attributable in part to faster acquisition speeds and a larger imaging area for O-8643. The C-4343 system exhibited superior imaging capabilities compared to C-4030, representing a quantifiable improvement over the original platform.