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KV-Energy Fan-Beam CT Imaging Performance of a Novel Biology-Guided Radiotherapy (BgRT) Machine

Z Sun1*, H Gao2, S Xu3, J Ye4, C Huntzinger5, S Shirvani6, S Mazin7, T Laurence8, (1) Reflexion Medical, Hayward, CA, (2) Tsinghua University, Haidian Dist, 11, CN, (3) Reflexion Medical, Hayward, CA, (4) Reflexion Medical, Hayward, CA, (5) RefleXion Medical, Hayward, CA, (6) Reflexion Medical, Hayward, CA, (7) Reflexion Medical, Hayward, CA, (8) Reflexion Medical, Hayward, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To provide a first report on the imaging performance of a fully integrated fast-rotation kV-energy fan-beam CT (kV-FBCT) scanner in a radiotherapy machine.

Methods: The RefleXion™ X1 radiotherapy machine is among the first linear accelerators to integrate a 16-slice kV-FBCT scanner for patient alignment and target localization. The kV-FBCT is located on the gantry ring of the radiotherapy machine. The CT imaging central plane is 386 mm from the treatment plane. The kV-FBCT has a curved detector with longitudinal coverage of 20 mm, a 50-cm field-of-view and an image matrix size of 512x512. Imaging is performed using helical scan mode wherein the couch moves at 10 mm/s, while the gantry housing both the CT scanner and the LINAC rotates at 60 RPM. kV-FBCT image quality was evaluated with a Catphan 600 phantom, a 20-cm-diameter water phantom, and a commercially available torso phantom.

Results: The measured image quality metrics of kV-FBCT under 1.25-mm nominal slice thickness are: (1) Water CT number accuracy: = 10 HU; (2) CT number uniformity: = 3 HU; (3) Image noise: 14.8 HU; (4) Scale and distance accuracy: = 1 mm; (5) In plane spatial resolution: = 9 lp/cm in test mode and = 4 lp/cm in clinical mode; and (6) Low contrast detectability: 5 mm object with 1% contrast. The dose level for these measurements was 2.54 cGy. Visual evaluations on the Catphan and torso phantoms demonstrate that kV-FBCT images have high-quality anatomical details and low contrast differentiation.

Conclusion: This is the first report of the kV-FBCT performance of the RefleXion X1 machine, indicating high image quality for radiotherapy localization and possible treatment adaptation based upon intra-course CT information. Future work will focus on assessing imaging performance in the setting of target motion.

Funding Support, Disclosures, and Conflict of Interest: Research supported by RefleXion Medical.


CT, Helical CT, Image-guided Therapy


IM- CT: Development (New technology and techniques)

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