Exhibit Hall | Forum 5
Purpose: MV scatter during kV image acquisition has been shown to significantly reduce the contrast-to-noise ratio of kV images. This reduction in image quality may impact the accuracy of markerless tumor tracking (MTT) particularly for dual-energy (DE) imaging. One mitigation strategy is to increase the kV detector system frame rate (reducing MV scatter) through vertical pixel binning. In this study, we assess the effect of vertical pixel binning on the accuracy of MTT for DE imaging.
Methods: A Varian TrueBeam (Varian Medical Systems, Palo Alto, CA) linear accelerator was used to acquire a series of interleaved 60 and 120 kVp images in Developer mode for 5 early-stage lung cancer patients using fast kV switching. DE logarithmic weighted subtraction was performed offline on sequential images to remove bone. Vertical pixel binning (2x1) was simulated on low and high energy projections prior to DE subtraction using in-house software to produce binned DE (DEB) images. Tumor motion on DE and DEB image sequences was tracked using a template-based matching algorithm. Tracking accuracy was evaluated using the tracking success rate (TSR), root mean square error (RMSE), the percent missing frames (%MFs). Ground truth positions from DE and DEB images were estimated using Bayesian inference.
Results: DE resulted in a TSR of 86.16.1%, RMSE of 1.43±0.4 mm, and the %MFs where the algorithm was unable to track of 2.3±1.0%. As compared to DEB images, the TSR, RMSE and %MFs were 85.9±7% (p >0.99), 1.42±0.4 mm (p = 0.81) and 2.5±0.9% (p = 0.50), respectively. Overall, the tracking results of DEB images were not statistically different than DE images.
Conclusion: Vertical pixel binning can be an attractive tool to increase the speed of the kV imager frame rate, potentially reducing the effect of MV scatter, without affecting the tumor tracking accuracy of DE images.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R01-CA207483. M. Lehmann, D. Morf, L. Zhu, and M. Walczak are employees at Varian Medical Systems.
Not Applicable / None Entered.
TH- External Beam- Photons: Motion management - intrafraction