Thermoacoustic Range Verification During Pencil Beam Delivery of a Clinical Plan to an Abdominal Imaging Phantom.

Thermoacoustic range verification is feasible for a hypofractionated protocol delivering 6 Gy/fraction at a conventional dose rate. Improving receive sensitivity by another 20 dB is WIP and could enable adaptive planning for 2 Gy fractionation or online verification before an entire hypofractionated dose is delivered at a conventional dose rate. SNR is proportional to dose/pulse so FLASH delivery with short (FWHM < 6 us) pulses would increase efficiency and could enable online verification before 1 Gy is delivered. Table 1. Time and range shifts between measured and simulated data compared to initial pressure per proton pulse and cumulative dose within the planned treatment spot. Beamlets from layer 2 that stopped in soft tissue in boldface.