UWM, Milwaukee, Wisconsin, USA
LBNL, Berkeley, California, USA
The potential of particle therapy due to focused dose deposition in the Bragg peak has not yet been fully realized due to inaccuracies in range verification. We report correlation of the Bragg peak location with target structure, by overlaying thermoacoustic localization of the Bragg peak onto a standard ultrasound image. Pulsed delivery of 50 MeV protons was accomplished by a fast chopper installed between the ion source and the inflector of the 88" cyclotron at Lawrence Berkeley National Lab. 2 Gy were delivered in 2 μs by a beam with peak current of 2 μA. Thermoacoustic emissions were detected by a clinical ultrasound array, which also generated a grayscale ultrasound image. Data was collected in a room temperature water bath and gelatin phantom with a cavity designed to mimic the intestine, where gas pockets can displace the Bragg peak. Experiments were performed with the cavity both empty and filled with olive oil. In the waterbath overlays of the Bragg peak agreed with Monte Carlo simulations to within 800±170 μm. Agreement within 1.3 ± 0.2 mm was achieved in the gelatin phantom, for which stopping power was estimated to first order from CT scans.
