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.