Assessment of TrueBeam kV Cone-Beam CT Image Quality and the Clinical Impact of Calibration Drift

This study compared the image quality of the TrueBeam (TB) kilo-voltage cone-beam CT (CBCT) system using standard reconstruction (TB-sCBCT) and iterative reconstruction (TB-iCBCT) with that of the Halcyon iterative CBCT (H-iCBCT). Additionally, the clinical impact of calibration drift over a one-year period was investigated for both head and pelvis imaging modes.

Image quality and calibration were assessed using the Catphan®. Image quality evaluation included the analysis of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and low-contrast detectability. Calibration stability for head and pelvis CBCT modes was examined by comparing dose-volume histogram (DVH) parameters across ten tongue and ten prostate patient cases.

The average SNR was 3.1 for TB-sCBCT, 23.1 for TB-iCBCT, and 6.9 for H-iCBCT, while the corresponding CNR values were 11.2, 53.0, and 28.4, respectively. At a contrast level of 0.3%, the smallest detectable target diameters were 15 mm for TB-sCBCT, 8 mm for TB-iCBCT, and 9 mm for H-iCBCT. Over a one-year period, the Hounsfield Unit (HU) variation in the head CBCT mode exceeded the recommended action threshold of ±50 HU, whereas the pelvis CBCT mode remained within acceptable limits.

In the TB system, advanced iterative reconstruction algorithms significantly enhance SNR and CNR by effectively reducing image noise. Halcyon provides improved image quality compared to TB with standard reconstruction; however, it remains inferior to TB-iCBCT. HU deviations were more pronounced in head CBCT than in pelvis mode, although HU variation in the pelvis CBCT mode exhibited greater sensitivity regarding clinical impact.