(Tuesday, 7/16/2019) 10:30 AM - 11:00 AM
Room: Exhibit Hall | Forum 5
Purpose: Establish independent user verification of manufacturer respiratory motion management phase data for patients with an implanted fiducial during lung SBRT.
Methods: Varian Real-Time Position Management (RPM) system is used to acquire time and external marker motion data for retrospective phase binning of the treatment planning 4DCT, real-time phase calculation during fluoroscopic imaging, triggered imaging, and beam on-off during gated treatment. The complex relationship between multiple parameters such as periodicity, predictive filter, and phase is described in general terms (i.e. “Savitsky- Golay smoothing�) in the manufacturer documentation. Respiratory data and images are exported for analysis using MATLAB with the imaging toolbox. Programs are able to automatically extract fiducial position as a function of time and to bin corresponding data according to phase which is more appropriate than lengthy time dependent display. Two major components examined for several breathing cycles on a representative patient were a comparison of fluoroscopic fiducial motion relative to 4DCT and variation of external marker motion for irregular breathing pattern.
Results: There is excellent correlation between the observed external marker motion and the fiducial motion in the fluoroscopic images. 4DCT tends to underestimate both the amplitude and diversity of the fiducial motion. Comparison of the fiducial motion on 4DCT and fluoroscopy immediately prior to treatment can indicate inappropriate margins, changes in phase gated window, and isocenter shift. Real-time computed phase compared to the predictive filter and retrospective computation indicates possibility for large variations which can affect actual position of the target within the gating beam on window.
Conclusion: The toolbox presented consisting of routines to automatically detect fiducial motion and correlate it with real-time and retrospective breathing cycle phase calculation is a valuable asset to evaluate individual patient motion management. Innovative phase binning presentation adds clarity and facilitates selection of specific cycles for further investigation.
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