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Determine Proton Pencil Beam Bragg Peak Position in 3D Through Acoustic Triangulation Algorithm

W Nie1*, J Sohn2 , S Li3 , X Yang4 , T Liu5 , A Kassaee6 , C Sehgal7 , S Avery8 , (1) University of Nebraska, Omaha, NE, (2) Emory University, Atlanta, GA, (3) University of Pennsylvania, Philadelphia, PA, (4) Emory University, Atlanta, GA, (5) Emory University, Atlanta, GA, (6) Univ Pennsylvania, Philadelphia, PA, (7) Univ Pennsylvania, Philadelphia, PA, (8) UNIVERSITY OF PENNSYLVANIA, Sicklerville, NJ


(Monday, 7/15/2019) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 6

Purpose: By measuring the time-of-flight (TOF) of acoustic waves generated by the thermoacoustic conversion of heat to pressure at the Bragg peak (BP), protoacoustics is a potential technique for proton range verification. The challenge of applying acoustic technique to proton radiation therapy is how to precisely determine the BP position in 3D with minimum dose. A homemade accelerometer array collected the acoustic signal produced in phantom, which was used to calculate the BP position in phantom through triangulation algorithm and compared to the simulation to verify the accuracy of this technique.

Methods: Protoacoustic signals induced by proton pulses from an IBA C230 cyclotron (FWHM=18μs) irradiating cylindrical (polyethylene) homogeneous solid phantoms were acquired by a five-accelerometer array placed on the distal surface of the phantom (see figure 1A). The acoustic signal were processed by a combination of high/low pass filters to obtain the Daubechies4 (db4) wavelet, which was used to obtain the acoustic TOF for each accelerometer. The difference of the TOF between paired accelerators indicates the BP position relative to the accelerators. Triangulation algorithm for the acoustic array was developed to calculate the BP in homogeneous phantom.

Results: Acoustic data processing using Daubechies wavelet method demonstrated that acoustic waves induced by ≤32 proton pulses were sufficient to obtain TOF with sub-microsecond uncertainty (figure2). Triangulation calculation suggests that a 5-transducer array is expected to allow for protoacoustic measurement of the BP position with an accuracy of 0.6 mm, which agrees with the preliminary experimental data.

Conclusion: Our study demonstrated that a 5-accelerometer array can be used to detected the protoacoustic waves induced in a patient by a clinic proton beam. The triangulation data processing algorithm can be applied to improve the accuracy of proton range verification with possible submillimeter accuracy with a point dose of 75cGy or less.


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