Miniature Optical Hydrophone for Detecting Proton Beam Range at Clinical Dose: An Initial Study
S Sueyasu1*, Y Sakuyama1, K Miyazaki2, M Unlu2,3, Y Kuriyama4, Y Ishi4, T Uesugi4, M Fujii5, M Kobayashi6, N Kudo7, Y Chen2,8, T Matsuura2,8, (1) Graduate School of Engineering, Hokkaido University, Sapporo, Japan, (2) Faculty of Engineering, Hokkaido University, Sapporo, Japan, (3) Department of Physics, Bogazici University, Bebek, Istanbul, 34342, Turkey, (4) Institute for Integrated Radiation and Nuclear Science, Kyoto University, Japan, (5) FAM Science Co., Ltd., Ibaraki, Japan, (6) Planetary Exploration Research Institute, Chiba Institute of Technology, Chiba, Japan, (7) Faculty of Information Science and Technology, Hokkaido University, Sapporo, Japan, (8)Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan
Presentations
PO-GePV-T-193 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
ePoster Forums
Purpose: Piezoelectric transducers are traditionally used to detect the acoustic signal produced from the impact of a proton beam; i.e., the ionoacoustic wave. However, due to the high-Z and paramagnetic properties of piezoelectric materials, positioning these transducers close to the beam may interfere with image guidance techniques such as X-ray fluoroscopy and magnetic resonance imaging, which are used during beam delivery. To overcome this, we tested a miniature optical hydrophone and assessed the range shift detection accuracy with homogeneous phantoms.
Methods: A 100-MeV proton beam with a pulse width of 27 ns and beam size of 4 mm was produced using a fixed-field alternating gradient accelerator and was irradiated to both the water and agar phantoms. The number of protons per pulse was 1.14 × 108, which is within the range used for clinical application. Acrylic plates of various thicknesses, up to 14 mm, were set in front of the phantoms to shift the proton range. The optical hydrophone (XARION Laser Acoustics GmbH) was set distal to the Bragg peak and the range was estimated using the time-of-flight method. In the agar phantom experiment, the hydrophone was embedded in a custom-made agar-based sensor head. Signals were low-pass filtered and recorded with a digital oscilloscope.
Results: Acoustic waveforms were clearly observed with a single-pulse measurement for both phantoms. The maximum estimation error of the range shift was 0.6 mm for the water phantom and 0.5 mm for the agar phantom. However, the estimated absolute range position varied by 2.6 mm between two independent experiments with the agar phantom.
Conclusion: Despite its small detector size, the optical hydrophone enabled detection of weak ionoacoustic signals produced by proton beams at clinical dose. Future studies should investigate the precise and optimal positioning of the detector on the deformable phantom surface.
Funding Support, Disclosures, and Conflict of Interest: Koichi Miyazaki is paid by Hitachi Ltd. and Masayuki Fujii is paid by FAM Science Co., Ltd.
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