Evaluation of the impact of slice thickness on CT and Cone Beam CT image quality in radiotherapy

Abstract

Author(s): Amine El Outmani*, M. Zerfaoui, I. Hattal, A. Rrhioua, D. Bakari, Y. Oulhouq, K. Bahhous

Objective: This study evaluates the accuracy of slice thickness and its impact on CT and Cone Beam CT (CBCT) image quality and dose distribution in radiotherapy. Materials and Methods: The Catphan 604 phantom was scanned using a CT scanner and a linear accelerator On-Board Imager. Images were acquired at 1, 3, and 5 mm slice thicknesses to assess the effects on low-contrast resolution, Hounsfield Unit (HU), Modulation Transfer Function (MTF), uniformity, and Contrast-to-Noise Ratio (CNR). Analysis and dose calculation were performed using Pylinac and Eclipse, respectively. Results: Greater measurement errors were detected for CBCT slice thickness compared to CT. Thinner slices improved resolution but increased noise, whereas thicker slices reduced noise but compromised detail. CT outperformed CBCT in terms of resolution, HU accuracy, uniformity, and CNR. Slice thickness had no significant effect on dose distribution, but differences were noted in bone structures between the modalities. Conclusion: Slice thickness significantly affects CT and CBCT image quality. Its verification is essential for optimizing radiotherapy imaging protocols.

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