S2064
Physics - Image acquisition and processing
ESTRO 2026
inner diameter 45 mm) contained inserts of air, distilled water, ethanol, K ₂ HPO ₄ , and PMMA. Endpoints were per-insert WEPL error ( Δ WEPL, mm and %) and per-projection scan time.
demonstrated significant improvements in quantitative accuracy and soft-tissue visualization metrics. The improved image fidelity may enable more accurate dose calculations and improved delineation of targets and normal tissues, an important step toward routine implementation of CBCT-based adaptive proton therapy. Keywords: Quantitative imaging, proton therapy, CBCT Digital Poster 1699 Proof-of-concept cone-beam Ion Computed Tomography (ion-CT) imaging system with a single scintillator-CMOS detector Tianyuan Wang 1 , Takashi Akagi 2 1 Department of Radiation Therapy Physics, Kobe Proton Center, Kobe, Japan. 2 Technology Development Department, Hyogo Ion Beam Medical Support, Kakogawa, Japan Purpose/Objective: Traditional SECT-based conversion from Hounsfield units to stopping-power ratio (SPR) is non-bijective and forces range-uncertainty margins of approximately 3- 3.5% plus 1-3 mm [1], enlarging treatment margins and increasing dose to organs at risk. Ion computed tomography (ion-CT) measures water-equivalent path length (WEPL) directly and has demonstrated sub- percent SPR accuracy [2]. Prior ion-CT scanners using multiple tracking planes and range detectors are complex and costly; early prototypes ran at 10-20 kHz requiring hours-long acquisitions [3], limiting clinical scalability. We present a simple cone-beam ion-CT approach using a single downstream scintillation- CMOS detector enabling clinically feasible, cost- efficient acquisition without compromising WEPL measurement quality. Material/Methods: We built an in-house light-tight scintillation-CMOS camera (ZnS(Ag) screen plus scientific CMOS) providing effective sampling of approximately 0.5 mm at the detector plane illustrated in Figure 1. Image acquisition was performed at Hyogo Ion Beam Medical Center synchrotron with 120 MeV/u protons, 150 MeV/u helium, and 210 MeV/u carbon delivered through a horizontal beamline. A rotation stage acquired cone-beam projections at 3° increments; we collected 60 views per half-rotation and mirrored them to 120 effective projections for reconstruction. Each projection underwent dark-/flat-field correction and conversion to WEPL via calibration curves from known water-equivalent thicknesses. In-house Feldkamp- Davis-Kress (FDK) cone-beam algorithm produced 3D WEL volumes. The cylindrical tissue-equivalent phantom (length 180 mm, outer diameter 105 mm,
Results: Acquisition time per projection averaged 15 s for carbon, 25 s for helium, and 30 s for protons, reducing total scan duration from several hours [3] to 15-30 minutes. Maximum WEPL deviations from ground truth were 0.03 cm (2.4%) for carbon, 0.02 cm (1.9%) for helium, and 0.04 cm (2.7%) for protons, demonstrating sub-millimeter accuracy across all modalities. Helium ion-CT exhibited superior 3D WEPL measurement accuracy, attributed to reduced lateral scattering relative to protons [4] and diminished nuclear fragmentation compared to carbon ions [5].
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