Thermoacoustics may enable quantitative dosimetry and real-time verification for particle therapy. Energetic ions enter the patient at relativistic speed, but come to a complete standstill within nanoseconds, depositing most dose near the final resting point. Concentrating dose at the Bragg peak minimizes collateral damage, and makes patient positioning more critical than for exponentially decaying x-ray radiation. Although interlocks halt treatment immediately upon detecting equipment failure, nothing defends against anatomical changes and patient motion. Whether on target or not, daily doses are delivered in their entirety, without benefit of real-time verification.
We will start with an overview of the physical phenomena that generate – and bandlimit - thermoacoustic emissions. Then, application to dosimetry and online verification will be discussed. In principle, fully 3D tomographic reconstructions of mathematically complete datasets can quantify dose during quality assurance testing. During therapy, however, only severely limited angle datasets are available. By combining with a priori information from the patient treatment plan the Bragg peak location can be estimated with accuracy exceeding the diffraction limit. Experimental results generated during delivery of a 6 Gy clinical plan by a synchrocyclotron (IBA S2C2) to an anthropomorphic phantom (CIRS 057A) will be presented