Evaluation of a Laser Doppler Vibrometer for Quality Assurance of FLASH and Conventional Proton Treatment
S Avery1*, J Liu2, W Nie3, A Kassaee4, L Dong5, M Pineda6, J Eichenberger7, K Parodi8, C Sehgal9, (1) UNIVERSITY OF PENNSYLVANIA, Philadelphia, PA, (2) New York Proton Center, New York, NY, (3) INOVA Schar Cancer Institute, Fairfax, VA, (4) University of Pennsylvania, Philadelphia, PA, (5) University of Pennsylvania, Philadelphia, PA, (6) Polytec Inc., ,,(7) Polytec, Inc., ,,(8) Ludwig-Maximilians-Universitat Munchen, Garching B. Munich, ,DE, (9) University of Pennsylvania, Philadelphia, PA
Presentations
TU-F115-IePD-F5-4 (Tuesday, 7/12/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 5
Purpose: Laser doppler vibrometer is a next-generation device that has high sensitivity (a resolution of 15 pm), a wider frequency response range (0–350 kHz), and it collects the acoustic signal without patient contact. Furthermore, we can use beamforming for customizable vibrometer arrays. These features make the laser vibrometer ideal to monitor proton therapy under FLASH and conventional conditions.
Methods: Measurements were taken under both conventional and FLASH dose rates – ranging from 1.6 – 71.6 Gy/s. Dose was calculated according to TRS 398 using a Markus chamber. We used polyethylene (PE), abdominal and brain phantoms in the study to determine feasibility. The vibrometer was compared with a hydrophone to determine the effect of SNR.
Results: Measurements were taken at 5 positions in the polyethylene phantom. The speed of sound in PE phantom is 2071m/s. We set the sample time to 12.8ms; our pulse generator is set to 100Hz (10ms). We found good agreement between measured and expected data. We used both the hydrophone and vibrometer for the abdominal phantom and found signal-noise-ratio (SNR) of vibrometer is 22.93, while the SNR of hydrophone is 4.216. The TOF in the brain phantom is 422.4 (±2.4) µs, corresponding to BP position of 3.36cm. The actual distance between BP to surface is 3.34cm with the percent error of 0.60%.
Conclusion: We are developing next-generation technology for an innovative technique to track both the conventional and ultra-high dose rate with sub-millimeter accuracy. Our study clearly has potential to be used in clinical proton therapy in the future. This project will provide a low-cost, easy to use, and robust technique for monitoring ultra-high dose rate proton therapy in vivo. We expect that this pre-clinical study will clarify concerns about the protoacoustic technique and lay the groundwork for translating this vibrometry technology for use in FLASH/concentional proton therapy in the future.
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