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Characterization of a Novel Kilovoltage Fan Beam CT System Integrated with a Ring Gantry Linac

G Gibbard1*, J Tan1, T Zhuang1, Y Park1, K Wang1, W Lu1, M Lin1, R Reynolds1, A Godley1, A Pompos1, S Jiang1, B Cai1, (1) UT Southwestern Medical Center, Dallas, TX,

Presentations

(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: This study aims to characterize the performance of the kV Fan-Beam Computed Tomography (kV-FBCT) imaging system on RefleXion X1 by use of national standards (TG40, TG142, TG148, TG179) and machine specific tolerances. RefleXion X1 is a novel radiotherapy machine that utilizes the kV-FBCT imaging system for IMRT, SBRT and Biology-guided Radiotherapy (BgRT). The kV-FBCT is used to guide patient setup and target localization.

Methods: Multiple imaging protocols were supported on this platform, tests were performed with a standard imaging protocol of 120 kV/1 s/150 mA/ 0.5 pitch/1.25 mm and 16 slice helical acquisitions. Standard image quality metrics, including slice thickness accuracy, Modulation Transfer Function (MTF) at 50%, spatial resolution, low-contrast resolution, geometric accuracy, contrast scale, CT Hounsfield unit (HU) number accuracy, regional uniformity & noise, and kV-MV Isocenter were evaluated using an image quality phantom (Catphan 500, The Phantom Laboratory, New York, NY), a water phantom (Jaszczak phantom) and Ball-Cube-II and Head Phantom.

Results: All major image quality metrics were within either the national guideline or vendor-recommended tolerances. The slice thickness, MTF at 50%, spatial resolution were measured to be 1.69 mm, 4.51 lp/cm, 9 lp/cm, respectively. The clinical spatial resolution and low contrast visibility was found to be acceptable with greater than 4 lp/cm and the smallest visible target less than 5 mm. The geometric accuracy tests passed within 1 mm at a 50 mm distance. The CT number uniformity is within 2.7 HU, contrast scale difference is within 0 HU. The CT number accuracy and noise are all within 15 HU. The total targeting error was less than 1 mm.

Conclusion: Comprehensive characterization of the kV-FBCT has been shown to provide acceptable image quality for image guidance. The image unit onboard the RefleXion X1 meets specifications and satisfies requirements for routine clinical use.

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Keywords

PET, Helical CT, Image-guided Therapy

Taxonomy

IM- Multi-Modality Imaging Systems: CT/PET - human

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