Program Information
Clinical Investigation of Auto Beam Hold and Intrafraction Motion Review
G Graeper*, A Cetnar , K Woods , N Gupta , M Weldon , James Cancer Hospital and Solove Research Institut, Columbus, OH
Presentations
TH-AB-205-11 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: 205
Purpose: This study investigates several new options for advanced imaging, including Intrafraction Motion Review and Auto Beam Hold. These functions allow the use of the On-Board Imaging system during treatment. The objective of our study was to investigate the accuracy of these new tools by studying dependence on imaging trigger, detection threshold, and imager angle.
Methods: Our experimental setup included a wax “tumor” nodule with implanted gold seeds which was inserted into a phantom. Trigger settings determine the frequency of imaging during treatment by way of particular MU, time, and gantry angle intervals. Here, dependence was tested by changing image acquisition trigger mode. A test was developed to examine dependence on threshold diameter magnitude. While holding all other variables constant, the thresholds were increased incrementally from 2 to 10 mm and the couch was shifted such that the seeds were on the cusp of their tolerance diameter. Angular dependence was tested by delivering a plan with static fields every 45° from gantry 0° to 180°. Data output was limited to the marker being within (pass) or outside (fail) of a set tolerance threshold. Data analysis was performed using pass/fail criteria of the fiducial matching algorithm.
Results: The pass rates for the trigger tests were consistent for each of the three triggering methods. There was no degradation in accuracy measured when changing the threshold diameter. At the majority of angles the angular dependence seems to be minimized, however there was some discrepancy seen, such as at 45°, where there was overlap of the markers causing identification issues of the fiducials.
Conclusion: Our study showed minimal accuracy changes in detection threshold and image trigger techniques. Based on our results care should be taken to place seeds on different axial planes to help reduce angular dependency of marker tracking.
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