J Ryser*, A Kassaee, C Sehgal, S Avery, UNIVERSITY OF PENNSYLVANIA, Philadelphia, PA

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  J Ryser

WE-B-202-6 (Wednesday, 7/13/2022) 8:30 AM - 9:30 AM [Eastern Time (GMT-4)]

Room 202

Purpose: To characterize and test a novel method of proton range verification using protoacoustics and piezoelectric film.

Methods: Using electrodes, we wired 25μm thick gold-coated polyvinylidene fluoride (PVDF) film to a PicoScope® to record the voltage produced in piezoelectric film (piezofilm). A relation between the applied force on the piezofilm and output voltage from the piezofilm was determined using two tests: one using metal balls of varying masses dropped on the film (producing forces of ~10N-80N) and one using sound waves produced by a pulse generator (producing forces ~0.003N-40N). We tested piezofilm of various areas (2cm²–144cm²) to determine the dependence of output voltage on film area. Using a 3x3cm² piezofilm, we delivered a pulsed proton beam (150MeV;100ns pulse-width) through a polyethylene phantom (ρ=0.93g/cm3;cs=2071m/s) to the piezofilm and recorded the voltage output signal with the PicoScope®. A photomultiplier tube determined the Bragg peak occurrence time.

Results: The relation between applied force and output voltage in the piezofilm was found to be linear for all film sizes. The pulse generator acoustic test yielded slopes of 2.82mV/N and 20.7mV/N for the 3x3cm² and 2x1cm² piezofilm, respectively. Output voltage increased exponentially with smaller film sizes, with exponential scaling factors of -0.028 and -0.009 for 3mV and 1mV of applied voltage, respectively. When placed in the proton beam beyond the Bragg peak, the piezofilm produced a distinct pulse signal for each proton pulse.

Conclusion: Acoustic waves resulting from the Bragg peak can be detected by piezoelectric film. Additionally, smaller film sizes produced higher output and were easier to manipulate. This reinforces the findings of previous simulation studies on protoacoustics and piezofilm. Going forward, the time-difference between the Bragg peak and the piezofilm signal can be determined, accounting for electronic delay. Thus, piezofilm has potential for use as a detector for verifying proton beam range.

Keywords

Protons, Thermoacoustics, Setup Verification

Taxonomy

TH- External Beam- Particle/high LET therapy: Range verification (in vivo/phantom): photoacoustic/optical

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