Room: Exhibit Hall | Forum 5
Purpose: In advanced radiotherapy, fiducial markers are frequently implanted near tumors that are subject to respiratory-induced motion for aiding with patient setup and respiratory gating. This study investigates the use of projection images acquired for pre-treatment cone beam computed tomography (CBCT) as a substitute to fixed gantry fluoroscopic imaging for pre-treatment tumor tracking and positioning.
Methods: Pre-treatment CBCT projections, and anterior-posterior (AP) and lateral (LAT) fluoroscopic sequences of 3 pancreatic and 3 liver SBRT patients with implanted fiducials, for a total of 26 fractions, were used. The number of implanted fiducials varied between 2 and 4. An offline research software (RapidTrack, Varian) was used to track the 3D position of fiducials in the CBCT projections and fluoroscopic images. The software implements a template matching and sequential stereo triangulation algorithm for 3D positional tracking and generates a correlation model with the external surrogate breathing signal (RPM, Varian).
Results: Line fitting was performed between the superior-inferior (SI) fiducial displacement and real-time position management (RPM) signal. The average correlation coefficients for both the CBCT and fluoroscopic projections were 0.96Â±0.03 and 0.97Â±0.02 respectively. The time gap between the CBCT and fluoroscopic acquisitions ranged from 4 to 11 minutes, and the average SI baseline drift between CBCT and fluoroscopic acquisition was -0.50Â±0.17 mm.
Conclusion: RapidTrack offline research tool shows the potential to track motion information of fiducial markers. Like fluoroscopic projection, CBCT shows a good correlation coefficient between internal and external motion. CBCT can as well eliminate the need for pre-treatment fluoroscopic pair acquisition, thus potentially reducing both the imaging dose to the patient and the total treatment time.
Funding Support, Disclosures, and Conflict of Interest: This study was funded by Varian Medical Systems, Palo Alto, California, USA