Ionoacoustic Dosimetry for FLASH Electron Beams: Design of Sensor Arrays and Reconstruction Algorithms through Computational Simulations

Particle therapy and FLASH radiotherapy offer promising advancements in cancer treatment. However, accurately measuring radiation dose within the body, especially in real-time and high dose rates characteristic of FLASH radiotherapy, poses significant technological challenges. Ionoacoustic methodologies offer an innovative and non-invasive approach to particle therapy dosimetry, leveraging the generation of acoustic waves from energetic particle interactions. As the initial pressure distribution of a ionoacoustic wave is linearly proportional to the absorbed dose, it is possible to reconstruct the dose distribution from the acoustic signals. This work explores the viability of ionoacoustic dosimetry through computational simulations of 9 MeV FLASH electron beams using the k-Wave toolbox in MATLAB with a variable number of sensors with the goal of maximizing the gamma index with a 1%/1 mm standard. Two different imaging algorithms were compared, and the results clearly indicate that interpolated time reversal (ITR) outperforms standard time reversal (STR) across virtually all sensor configurations. Remarkably, ITR achieves high-quality image reconstruction with a significantly lower number of sensors. For instance, using ITR acceptable images (above 90% of the gamma index less than 1) were produced with as few as 24 sensors, 78% less than the ones necessary for STR, which required at least 108 sensors to reach a similar accuracy of 90.75%. When using 108 sensors, ITR demonstrated a 99.80% accuracy, representing an improvement of 46.25 times over STR.