Transducer Specifications for Thermoacoustic Range Verification SK Patch, R Lindert, UW-Milwaukee D Hoff, T Webb, LG Sobotka, Washington University Saint Louis T Zhao, Washington University Medical Center Best viewed in presentation mode on a Windows PC with audio enabled !! Particle Therapy Cooperative Group North America Annual Conference Chicago, October 23-25, 2017

Motivation Transducers should be sensitive to thermoacoustic emissions Outline simulation assuming instantaneous deposition – Monte Carlo + acoustic pulse envelope measured on Mevion S250 account for measured pulse envelope

Forward Simulation of Thermoacoustic Emissions - Instantaneous Deposition SRIM/TRIM Monte Carlo using water target 90k protons at 230 MeV beam σ = 3.3 mm in air upon entry into target position and energy recorded every 1 MeV custom software distributed energy loss uniformly along line segments – 1 mm discretization 3D k-Wave software propagated thermoacoustic pressures due to instantaneous deposition, pδ, results below for transducer located distal along beamline

S250 Pulse Envelope Measurements 1 mm x 1 mm x 6” scintillating fiber attached to a PMT 1 mm x 6” face placed in the beam triggered on the injection of hydrogen into the synchrocyclotron beam intensity reduced until only a few spikes per trigger (blue) inverted & summed 400 waveforms (red) FWHM = 5.8 μs , nearly Gaussian histogram of sum 1 of 400 realizations

Stress Confined TA Signal Generation Positive (compressional) followed by weak negative (rarefactional) Build up pressure faster than it runs away 6 μs pulsewidth → Slight loss of pulse amplitude and bandwidth initial pressure > 0

Analysis pδ bandlimited below 150 kHz, pI below 100 kHz for FWHM= 6 μs Convolved TA emissions with Gaussian to simulate experimental emissions pI = pδ * I, where I is Gaussian with FWHM = 6 μs pδ bandlimited below 150 kHz, pI below 100 kHz for FWHM= 6 μs pI amplitude also diminished

Discussion CUSTOM ULTRASOUND HARDWARE REQUIRED!! Pulse amplitudes very low, O(10 Pa), require sensitive receivers Receive-only TA transducers should be sensitive to 0-150 kHz, not MHz Signals received at lateral transducer locations are even lower frequency Heavier ions may generate broader band signal because Bragg peak is sharper – pulse envelope likely to limit bandwidth Acknowledgements: Jeff Heine, Patrick Zerkel (Mevion Engineering) - and many PT physicists for helpful discussions, including next speaker, Jiajian Shen

Discussion – heavy ions better, with stress-confinement Heavier ions may generate broader band signal because Bragg peak is sharper – pulse envelope likely to limit bandwidth TRIM simulations comparing C vs H in water, distal transducer location carbon emissions stronger and broad band compared to proton