The Standardization of Cone Beam Computed Tomography (CBCT) Presets on the Elekta XVI System for Optimized Image-Guided Radiotherapy (IGRT)

Abstract

Image-Guided Radiotherapy (IGRT) relies on accurate imaging systems to ensure precise patient positioning and target localization. Cone-Beam Computed Tomography (CBCT) integrated into the Elekta XVI platform enables volumetric imaging with soft-tissue visualization, but image quality and patient dose strongly depend on acquisition parameters, or “presets.” This study presents a comprehensive methodology for standardizing CBCT presets on the Elekta XVI system to optimize image quality, geometric accuracy, and radiation dose according to the ALARA (As Low As Reasonably Achievable) principle. Eighteen acquisition configurations were systematically evaluated by varying tube potential, tube current, exposure time, filtration, collimation, gantry speed, and projection number. Radiation dose was measured using a calibrated ionization chamber, while image quality was assessed through Catphan 503 phantom analysis using the PyLinac software, quantifying uniformity, contrast-to-noise ratio (CNR), spatial resolution (MTF), and geometric accuracy. Results showed that tube potential (kV) was the dominant factor influencing image uniformity (ρ = 0.674, p = 0.0229) and contrast (ρ = 0.676, p = 0.0225), while dose scaled linearly with tube current and exposure time. Bow-tie filtration (F1) reduced central dose by approximately 25% and improved CNR. Geometric accuracy remained within ±1 mm for all protocols. Based on these quantitative relationships, standardized clinical presets were established for distinct anatomical sites (Head and Neck, Chest, Prostate and Pelvis), combining higher tube potential with reduced mAs to balance photon penetration, image contrast, acquisition time, and dose efficiency. The resulting protocols ensure reproducible image quality, and minimized patient exposure. This framework demonstrates that data-driven standardization of CBCT presets enhances both safety and precision in daily IGRT practice and provides a foundation for future adaptive radiotherapy integration.