Abstract
BACKGROUND: Image-guided particle therapy (IGPT) has significantly advanced in recent years, particularly in the context of proton therapy. However, imaging solutions for carbon-ion radiotherapy (C-ion RT) remain limited. PURPOSE: This study introduces sliding-gantry cone-beam computed tomography (CBCT) and dual-panel digital radiography (DR) systems, both mechanically independent of carbon-ion delivery nozzles. We aim to evaluate the image quality metrics and verify the positioning accuracy of the imaging systems. METHODS: Image quality was evaluated in terms of spatial resolution, low contrast resolution, image uniformity, and effective imaging area using a multi-purpose imaging phantom, Catphan 700 phantom, and ImageJ software. The influences of planning computed tomography (CT) slice thicknesses (1-5 mm), radiation quality settings (90-130 kV), and registration algorithms (bony, grayscale, and fiducial marker registrations) on positioning accuracy were assessed using anthropomorphic head-neck and thoracoabdominal phantom images. The clinical feasibility of both systems was validated in 22 enrolled patients. RESULTS: The CBCT exhibited a lower in-plane spatial resolution (2.50 line pairs per millimeter (lp/mm)) than DR (2.80 lp/mm). Spatial resolution of the CBCT system was measured at 0.90 lp/mm using the CTP 714 module of the Catphan 700 phantom. Both systems achieved a low contrast resolution of 2.30%. DR provided superior image uniformity (1.12%-1.40%) compared with CBCT (2.20%). The effective imaging areas were comparable between the CBCT and DR systems (99.30%-99.50%). Positioning accuracy varied with planning CT slice thicknesses, radiation quality settings, and registration algorithms, showing mean translation displacements ranging from 0.01 to 0.48 mm. CBCT achieved inter-fraction translational positioning errors within 2 mm in 42.3% (22/52) of fractions and rotational positioning errors within 2° in 80.8% (42/52) of fractions, and DR achieved 33.8% (24/71) and 73.2% (52/71), respectively. CONCLUSION: The developed CBCT and DR systems achieved superior image quality and sub-0.5 mm positioning accuracy. These findings support the clinical feasibility of integrating CBCT and DR imaging systems into the C-ion RT workflow.