Description
Thermoacoustic emissions are generated by pulses of ionizing radiation (thereafter referred to as ionoacoustics) depositing their energy in a medium. For single ionizing pulses or pulse trains much shorter than the time it takes for the acoustic wave to propagate through the heated volume, the pressure produced varies linearly with the dose per pulse. In these conditions, the pressure is also directly related to the spatial dose distribution in homogeneous media. Therefore, monitoring the time-of-flight, shape and pressure amplitude enables the localization and characterization (beam size and dose deposited) of the ionizing source. Ionoacoustics-based dosimetry has been developed in the last decade at the Medical Physics department of the LMU Munich as an online monitoring tool for pulsed particle beams in conventional proton beam therapy and for laser-driven proton beams. For the latter, the I-BEAT (Ion-Bunch Energy Acoustic Tracing) detector has been implemented at the Centre for Advanced Laser Applications (CALA) for beam diagnostic. By recording the acoustic signal emitted by a single proton bunch stopping in a water volume, I-BEAT enables prompt reconstruction of bunch parameters such as mean energy, energy spread, lateral position and particle number from the recorded acoustic trace on a shot-to-shot basis. The technique is inherently resistant to the strong electromagnetic pulse environment associated with laser-plasma interaction and remains operable at the high particle fluxes typical of laser-accelerated ion sources.
Building on these knowledge, ionoacoustic monitoring has been implemented in a controlled accelerator environment using very high-energy electron (VHEE) at the CERN Linear Electron Accelerator for Research (CLEAR) user facility to support ongoing in vivo irradiation experiments with zebrafish embryos. Acoustic emissions generated in 28°C water by single electron bunch and pulse trains were detected over a broad range of deposited doses, with signal amplitudes consistently scaling with both instantaneous and cumulative delivered dose. The current setup enables reconstruction of beam position and diameter with millimeter-level accuracy, providing spatially resolved information on the delivered dose during irradiation and demonstrate good agreement with CLEAR reference dosimetry tools (EBT3 gafchromic films and charge measurement) during embryo irradiation.
Ongoing work aim to improve absolute dose reconstruction by accounting for temperature-dependent acoustic properties, sensor response, and beam time structure. Future experiments will extend this approach to in vivo irradiation with laser-driven proton beams at CALA, to enable reliable shot-resolved monitoring of delivered dose in preclinical irradiation conditions.
Acknowledgements: DFG (540410528), LMUexcellent, SNF, CALA, GSI-LMSCH2025
