S2104
Physics - Image acquisition and processing
ESTRO 2026
Purpose/Objective: Accurate imaging is fundamental for effective
Results: iCBCT MAR provided a pronounced reduction in metal- induced artifacts for all tested metals. Artifact suppression depended on the distance from both the metallic insert and the phantom surface, reflecting the algorithm’s limited effectiveness for objects located directly at the boundary. Despite manufacturer statements regarding reduced efficiency for low- density metals, this study did not observe a measurable degradation in reconstruction performance for titanium or materials with density similar to soft tissue. Across evaluated inserts, MAR reduced HU deviations relative to reference values ( Δ ref) and lowered standard deviations, demonstrating increased image uniformity (Table 1). Improvements were most notable for soft-tissue-equivalent regions (brain, water-equivalent insert), while bone showed a smaller but consistent enhancement. Conclusion: The iCBCT MAR reconstruction significantly improves image quality and HU stability in the presence of metallic implants. Although the algorithm does not fully eliminate deviations—especially near the phantom edge—it consistently yields more homogeneous images and more reliable HU values than standard iCBCT. These findings confirm that iCBCT MAR enhances quantitative imaging accuracy, supporting more precise radiotherapy planning and dose delivery, while highlighting the need for cautious interpretation of HU values in the immediate vicinity of high-density objects. References: 1. TrueBeam Hypersight Quick Start Guide, Varian Medical Systems, 2025 Keywords: metal artifact reduction, hypersight, MAR Evaluation of inter-patient spatial normalisation for voxel-based analysis in magnetic resonance- guided adaptive prostate radiotherapy Kongpop Chukly 1 , Tanwiwat Jaikuna 1 , Tissana Prasartseree 1,2 , Thee Mateepithaktham 1 , Sumetha Fang 1 , Naphat Komenake 1 , Akrapol Suppasedtanon 1 , Paritt Wongtrakool 1 , Ratchapas Romrattaphan 1 , Natthanicha Sauenram 1 , Naritsa Rotmuenwai 1 , Wiwatchai Sittiwong 1,2 , Pongpop Tuntapakul 1 , Wajana Thaweerat 1 , Pitchayut Wongsuwan 1 , Marianne Aznar 3 , Eliana Vasquez Osorio 4 , Pittaya Dankulchai 1 1 Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. 2 Department of Digital Poster Highlight 5150
radiotherapy planning and delivery. Metal-induced artifacts remain one of the most significant challenges, compromising lesion localization, tissue differentiation, and IGRT-based patient positioning. To mitigate these issues, metal artifact reduction (MAR) techniques have been developed for CT machines and recently for Varian machines. The aim of this study was to verify the accuracy of Hounsfield Unit (HU) reconstruction by the iCBCT MAR algorithm (HyperSight, Varian Medical Systems, USA) in the presence of metallic inserts. The study further assessed reconstruction accuracy for different metals with varying densities and physical properties. Material/Methods: Scans were acquired using the HyperSight iCBCT system and reconstructed with both the standard iCBCT algorithm and the MAR variant. According to the manufacturer, the iCBCT reconstruction improves soft- tissue visualization and HU accuracy, while MAR specifically reduces metal-related artifacts, albeit with limitations near the surface and for materials of bone- like density. A Cheese Phantom (Accuray, Madison, USA) with tissue-equivalent inserts and metallic inserts was used (Fig 1). Metals included titanium ( ρ = 4.5 g/cm ³ ), Alloy-600 ( ρ = 8.5 g/cm ³ ), tungsten ( ρ = 19.3 g/cm ³ ) were used. HU accuracy and standard deviation were assessed in ARIA (Varian) system.
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