Task-based image quality and dosimetric validation of HyperSight CBCT for adaptive radiotherapy.

BACKGROUND: Cone-beam computed tomography (CBCT) is increasingly used in adaptive radiotherapy (ART), yet the dosimetric accuracy and image quality of advanced CBCT imaging platforms-such as Halcyon HyperSight 4.0 (HH), which combines an upgraded detector panel with advanced iterative reconstruction, scatter-correction, and metal-artifact-reduction algorithms-remain insufficiently characterized clinically. PURPOSE: To evaluate HH CBCT reconstruction algorithms for ART by assessing image quality, dose accuracy, and in vivo verification using optically stimulated luminescence dosimeters (OSLDs). METHODS: Task-based image quality was evaluated with ImQuest per AAPM TG-233 using a Gammex 464 ACR phantom on three systems: Canon Aquilion Large Bore CT (LB, reference), TrueBeam (TB), and HH. Seven algorithms were compared (LB, TB-FDK, TB-iCBCT, HH-FDK, HH-iCBCT, HH-Acuros, HH-MAR), with d' (the detectability index, a task-based image-quality metric per AAPM TG-233) derived for four insert materials (polyethylene, acrylic, bone, air). A volumetric modulated arc therapy (VMAT) plan was independently re-optimized (using identical optimization objectives/constraints as the LB reference plan) on HH-iCBCT, HH-Acuros, and HH-MAR images and verified by portal dosimetry (1%/1 mm gamma), delivered to an Alderson RANDO phantom with dose measured at 15 points (2 clinical target volume [CTV], 7 organ-at-risk [OAR], and 6 lung points) using BeO OSLDs and compared to LB (± 5% criterion). Mean d' per algorithm was compared to LB via one-sample t-tests (p < 0.05). RESULTS: HH-iCBCT (d' = 4.70, p = 0.016), HH-Acuros (d' = 4.61, p = 0.005), and HH-MAR (d' = 4.71, p = 0.024, numerically highest) showed significant detectability improvement over LB (d' = 4.42), with HH-iCBCT most consistent across materials. Mean absolute OSLD dose errors were 1.71%, 2.09%, and 2.90%; all 15 points met the ± 5% criterion except Lt_lung2 in HH-MAR (-5.32%). CONCLUSION: HH-iCBCT demonstrated clinically acceptable image quality and dose accuracy for CBCT-based ART, supported by in vivo BeO OSLD verification in an anthropomorphic phantom.