Hypersight CBCT on Conventional Linac for Adaptive Prostate Radiotherapy: Evaluating Image Quality, HU Stability, and Metal Artifact Reduction
Abstract
Purpose
Kilovoltage cone-beam CT (kV-CBCT) is routinely used for image-guided radiotherapy (IGRT). However, image artifacts and limited Hounsfield unit (HU) stability strict its application in adaptive radiotherapy. Recently, HyperSight CBCT was introduced to C-arm linear accelerators with improved detective quantum efficiency (DQE) and advanced reconstruction techniques, offering potential opportunities for CBCT-based adaptive planning. This study evaluates the feasibility of C-arm–mounted HyperSight CBCT for adaptive prostate radiotherapy by assessing image quality, HU stability, and metal artifact reduction using phantom and prostate patient data.
Methods
HyperSight CBCT images were acquired on a Varian Edge linear accelerator, and reconstructed using three
Methods
standard CBCT, iterative CBCT (iCBCT), and metal artifact–reduced iterative CBCT (MAR-iCBCT). Longitudinal HU stability was evaluated in CBCTs from six prostate cancer patients (five fractions each) using mean absolute deviation (MAD), as well as in a phantom scanned on multiple days. CBCTs from five additional patients acquired with a pre-HyperSight system were compared. Pelvic organs were auto-segmented using an AI-based tool, and metal artifacts were quantified by measuring HU standard deviation (SD) in regions surrounding implanted fiducial markers. Agreement between reconstruction methods was assessed using intraclass correlation coefficients (ICC).
Results
MAR-iCBCT demonstrated substantial reduction of metal-induced artifacts compared with iCBCT and standard CBCT, with the lowest HU SD in fiducial-adjacent regions. Both iCBCT and MAR-iCBCT provided improved soft-tissue contrast relative to standard CBCT. Inter-fraction HU variability was similar across HyperSight reconstructions, with MAD values below 5 HU for phantom, and below 10 HU for nearly all pelvic organs. Median HU values were closely aligned between iCBCT and MAR-iCBCT (ICC > 0.97), while standard CBCT showed systematic offsets.
Conclusion
C-arm–based HyperSight MAR-iCBCT significantly improves image quality, reduces metal artifacts, and demonstrates robust HU stability and agreement, supporting its feasibility for CBCT-based adaptive prostate radiotherapy.