Program Information
Thermoacoustic Range Verification Using Oblique Beams - TOPAS+k-Wave Simulations
T Zhao1*, S Patch2 , (1) Washington University School of Medicine, St. Louis, MO, (2) UW-Milwaukee Dept. of Physics
Presentations
MO-F-CAMPUS-JT-2 (Monday, July 31, 2017) 4:30 PM - 5:30 PM Room: Joint Imaging-Therapy ePoster Theater
Purpose: To demonstrate thermoacoustic verification of proton range in proton therapy. Robustness of the verification on the orientation of ultrasound array with respect to beam direction was also investigated and reported.
Methods: TOPAS Monte Carlo simulations with one million protons modeled energy density deposited by a horizontal beam (Gantry angle 90°) and an oblique pencil beam (Gantry angle 48°) in a prostate case. Multiple scenarios were simulated for each beam angle, with range translated deliberately in ±5 mm increments. The energy density was computed on the same mesh as the planning CT, with 1 mm spatial discretization. A uniform Grueneisen of 0.1 was assumed, but a three-speed soundspeed map was generated using the planning CT with 3200 m/s, 1540 m/s and 1480 m/s for bone, muscle and organ, and fat tissues, respectively. Three-dimensional K-wave simulations propagated thermoacoustic pulses throughout the planning CT volume, and they were recorded at virtual transducer locations along a 5 cm line segment, mimicking a sidefire transrectal ultrasound (TRUS) array placed distally and laterally to the oblique and lateral pencil beams respectively. One-way beamforming of recorded thermoacoustic pulses yield range estimates in the sagittal plane of the TRUS array.
Results: Measurements of thermoacoustic emissions generated during oblique delivery were highly sensitive to range change. However measurements of emissions due to horizontal beams were insensitive to range change. Range estimates from one-way beamforming in the sagittal plane defined by the TRUS array track range shifts of oblique beams with 1 mm accuracy (matching resolution of planning CT), but did not follow lateral beams as range is shifted.
Conclusion: Thermoacoustic verification shows great potential in monitoring proton range in vivo. However, sensitivity varies with the location and orientation of the ultrasound array with respect to beam angle.
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