Program Information
Accurate Measurement of Couch Walk Using MV/KV Imaging
Y Song*, B Mueller, C Obcemea, J Jeong, Z Saleh, X Tang, M Zinovoy, D Gelblum, B Mychalczak, Memorial Sloan Kettering Cancer Center Westchester, West Harrison, NY
Presentations
TU-C1-GePD-J(B)-6 (Tuesday, August 1, 2017) 9:30 AM - 10:00 AM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: Couch walk is commonly measured with a sheet of fine grid graph paper and a front pointer. Although this method is conceptually simple and easy to implement, its accuracy is compromised by the poor precision of the graph paper grid and the large size of the front pointer tip. In this study, we developed a novel technique for measuring couch walk using HD MV/KV imaging. Our objective was to improve the measurement accuracy to within 0.1 mm.
Methods: The couch LAT and LNG shifts were measured with MV imaging and the VRT shift was measured with KV imaging on a CBCT cube phantom containing a 6-mm diameter steel ball bearing. With couch at 0°, the phantom was aligned with the machine cross-hair. An AP MV image was acquired. Using a center detection function, the geometric center of the ball bearing was determined and aligned with the mechanical isocenter. The couch was then rotated by 5.0° each time. An AP MV image was acquired and the geometric center of the ball bearing was detected again. The new coordinates represented the couch LAT and LNG shifts at this couch angle. For KV imaging, the KVD was rotated to 90° and the couch was lowered to prevent collision. Then, the above procedure was repeated to measure the couch VRT shift.
Results: With our approach, a couch shift of 0.1 mm was easily detected. We found that there were essentially no shifts in VRT. LNG also exhibited very minimal shifts. Most shifts occurred in LAT, as observed clinically with AlignRT. Among the four TrueBeam machines that we measured, the maximal couch shift was 0.4 mm.
Conclusion: Based on our investigations, we believe that couch walk measurement with MV/KV imaging is an accurate and practical technique. With some efforts, this procedure can be automated.
Contact Email: