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Towards In Vivo Localizing Proton Bragg Peak With Proton-Acoustic Imaging

Y Zhao1*, Y Chen2 , S Wang1 , J Merrill1 , P Samant1 ,J Arellano1, S Ahmad2 , T Herman2 , L Xiang1 , (1) University of Oklahoma, Norman, OK (2) University of Oklahoma Health Science Center, Oklahoma City, OK


(Wednesday, 7/17/2019) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 1

Purpose: To localize the proton Bragg Peak by measuring the acoustic emissions generated by a pulsed proton spill from a clinical synchrocyclotron, ideally in real-time and noninvasively during patient treatment.

Methods: A three-dimensional (3D) volumetric ultrasound imaging system based on 1MHz two-dimensional matrix array ultrasound probe with 256-elements, a 256-32ch switch and a parallel data acquisition system has been developed. The matrix array will now be placed in a water tank in front of the proton nozzle which enables rendering of the proton-induced acoustic images without mechanical scanning. The data acquisition will be synchronized by a trigger signal provided by the MEVION S250i Hyperscan proton therapy system. The digitized data will then be sent to the computer for real-time processing to generate proton-acoustic images with a full-field 3D filtered back-projection algorithm.

Results: Hyperscan system has pulse width modulation from 0.5 to 20 us. On average, a full energy (230 MeV) pulse of 6.5 us produces 8 pC (~5x 10^7 protons) and deposits 3.2 cGy under Bragg peak. The total dose distribution of scanned proton pencil beams was simulated. The maximum spatial resolution of the proton-acoustic imaging modality was calculated to be about 1 mm, which is much better than the current range verification techniques proposed, for example, positron emission tomography and prompt gamma imaging. In addition, the proton-acoustic imaging system can obtain 50 frames of images per second without scanning, which means real-time in vivo images could be obtained during treatment to ensure the delivered dose distribution is as expected.

Conclusion: These results highlight the excellent prospect of the 3D volumetric proton-acoustic imaging in clinical transformation providing the Bragg peak location, and monitoring proton dose distribution during radiation therapy.


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