Ionoacoustics in time and frequency domain: A novel method for direct in vivo measurement of the Bragg peak position in ion beam therapy

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Range verification is the crucial issue in ion therapy to enable full clinical exploitation of its characteristic advantages over photon therapy. Methods currently under clinical testing rely on nuclear imaging techniques, which require complex and costly detector systems. Moreover, nuclear-based methods do not provide direct correlation between the dose maximum (Bragg peak) and the emission signal. In our approach, we intend to make use of the pressure pulse and related acoustic wave induced by ions stopping in tissue (hence ionoacoustics) to measure the ion range with ultrasound methods. This technique promises a simple and direct possibility to correlate, in vivo and in real-time, the conventional ultrasound echo of the tumor region with the characteristic signal of individual Bragg peaks delivered with the most advanced pencil-beam irradiation schemes. The challenge entails the small pressure pulse at clinical conditions, as shown in first experimental tests. The goal of this project is to demonstrate experimentally the detection of the weak ionoacoustic signal and its utilization for accurate identification of the Bragg peak position under clinical-like conditions. For this purpose, we will develop new methods of ionoacoustic detection in time and, in particular, frequency domain, and then perform extensive validation and refinement at proton beams. The goal will be achieved by using an intensity modulated energy deposition, which can be initially developed at an optoacoustic setup. In the second part of this project we will pursue experiments at proton accelerators with appropriate energies and beam conditions. Finally, we will engage in the development of new image reconstruction techniques, aiming at correlating the Bragg peak position with an ultrasound image, thus paving the way towards future deployment of this unique and promising technique in tumor therapy. Although the project is focused on proton beams, the ionoacoustic technique could also find application for heavier ions.