Room: Karl Dean Ballroom B1
Purpose: By measuring the time-of-flight 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. To understand the ideal detector for possible Â¬in vivo or beam quality assurance (QA) protoacoustic applications, we investigated three different acoustic detectors â€“ a hydrophone, accelerometer, and laser vibrometer â€“ and characterized a triangulation method through simulation.
Methods: Protoacoustic signals induced by proton pulses from an IBA C230 cyclotron (FWHM=18Î¼s) and IBA S2C2 synchrocyclotron (FWHM=10Î¼s) irradiating rectangular (aluminum and lead) and cylindrical (polyethylene) homogeneous solid phantoms were measured. Three detectors were used: a hydrophone accelerometer and laser vibrometer. To investigate triangulation algorithms, the polyethylene phantom CT was used to map the density and sound speed for psuedospectral wave-equation simulations (k-Wave MATLAB toolbox).
Results: The hydrophone-, accelerometer- and laser vibrometer-measured protoacoustic signals exhibit similar acoustic echo features in confined solid phantoms. The protoacoustic signal-to-noise ratio (SNR) measured by the hydrophone on IBA C230 cyclotron was 28.6, compared to 22.5 and 9.9 measured by the accelerometer on IBA C230 and IBA S2C2, and the SNR of protoacoustics was measured as 12.0 by vibrometer on IBA S2C2. When solid water is introduced to pull back the proton range, the non-contact laser vibrometer successfully captures the BP shifts. Based on the homogeneous material simulations, a 5-transducer array is expected to allow for protoacoustic measurement of the BP position with an accuracy of 0.6 mm.
Conclusion: Our study shows that laser vibrometer may provide a novel, non-contact method to monitor 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 in 3D with possible submillimeter accuracy compared to our measurements using single acoustic detector.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this abstract was supported by the NATIONAL INSTITUTE OF BIOMEDICAL IMAGING AND BIOENGINEERING (NIBIB) of the National Institutes of Health under award numberR21 CA205063. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.