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Real-Time Beam-Eye-View Monitoring of Prostate Motion During IMRT: A Moving Phantom Study with Cine-EPID Imaging

X Chen

X Chen1*, J Fan1, J Xue1,2, L Chen1, L Wang1, C Ma1, (1) Fox Chase Cancer Center, Philadelphia, PA, (2) Cancer Center of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology Wuhan, P.R. China

SU-E-J-46 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Intrafractional tumor motion introduces significant dose uncertainty for radiotherapy. Using the portal imaging during IMRT delivery will provide a real-time beam-eye-view (BEV) tumor motion observation. We have developed a gradient-based gold seed fiducial detection algorithm for MV portal imaging. The purpose of this study is to investigate the use of the algorithm for prostate motion monitoring during external beam IMRT treatment by using a moving phantom with cine-EPID imaging.

Methods: A pelvic phantom mounted on a moving stage was used to mimic prostate patient during IMRT treatment. IMRT fields were delivered to the pelvic phantom with a gold fiducial (1x5 mm) on the Varian Trilogy. Cine-EPID images were acquired using Varian aSi1000 EPID system with the following settings: continuous mode, 3 averages per image, image size 1024x768 with resolution 0.392mm per pixel, EPID at 140cm SID (source-imager-distance).

Results: Twenty IMRT fields were delivered and about 250 EPID images were acquired while the pelvic phantom was moving in a sinusoidal pattern. Gold seed fiducial was visible in about 40% of EPID images but was blocked by MLC in the remaining images. A gradient-based algorithm was able to detect the fiducial successfully and recorded the fiducial location at different time.

Conclusion: Intrafractional tumor motion is a clinical concern which cause dosimetric uncertainty delivered to patients. By using cine-EPID imaging during IMRT delivery combined with an automatic fiducial detection algorithm, beam-eye-view tumor motion can be observed and recorded which may be used for on-treatment tumor motion management. This moving phantom study showed the real-time BEV monitoring of prostate motion during beam delivery is feasible and may be clinical practical.

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