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BEST IN PHYSICS (THERAPY) - Use of Radiation-Induced Ultrasound to Image Proton Dosimetry

K Stantz

K Stantz1*, F alsanea1, V Moskvin2, (1) Purdue University, West Lafayette, IN, (2) Indiana University- School of Medicine, Indianapolis, IN

TH-C-144-1 Thursday 10:30AM - 12:30PM Room: 144

Purpose: The objectives of this study are to simulate the ionizing radiation induced thermoacoustic signal from scanning proton beam; and investigate the various designs and techniques of ultrasound tomographic imaging to map three dimensional dose (3D) proton dose distributions.

Methods:A 3D dose and proton fluence distribution in a water phantom from a scanning spot beam from a treatment nozzle was simulated using a Monte Carlo (MC) code FLUKA (v. 2012) for 6.5 , 16 and 27 cm proton range. An initial radio-acoustic computed tomographic (RCT) scanner design of a cylinder with 128 transducer array (0.5MHz center frequency; 50% bandwidth at -6dB; flat surface) centered along the height of the cylinder (z-axis) at a radial distance of 15 cm was evaluated. The thermoacoustic generated pressure signals from the proton beam were simulated and digitally sampled for each transducer over time, which was rotated over 30 angles about isocenter. A 3D filtered backprojection algorithm was used to reconstruct the dosimetric image volume consisting of the Bragg peak (initially at 5x5x5mm3), and then compared to the MC results.

Results:The comparison between the beam profiles as simulated by MC and measured from commissioning of the beam had an estimated deviation of about 2%. An analysis of the RCT intensity dependence on depth as compared to MC simulated data demonstrated that the distal edge of the Bragg peak was within binning size of the reconstruction image and MC position prediction, with an average variation in RCT intensity around 6%.

Conclusion:This feasibility study demonstrates that RCT can be used to monitor the dose distribution and proton range in proton therapy. Additional scanner designs (geometry, transducer bandwidth consideration, phantom designs) will be investigated and presented, such as phase-array methods. Acquiring measurement data to compare with the simulated data is work in progress.

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