Volumetric FLASH dosimetryin vivousing real-time radiacoustic imaging.

Objective.The main goal of this research is to verify the spatial fidelity of radiacoustic imaging (RAI) as a quantitative dosimetric monitoring tool for FLASH radiotherapy (FLASH-RT)in vivo. FLASH-RT delivers therapeutic radiation at ultra-high instantaneous dose rates (>106Gy s-1), offering substantial reductions in normal tissue toxicity while maintaining tumor control. However, clinical translation remains limited by the absence of real-time,in vivodosimetry systems capable of resolving dose delivery at microsecond timescales.Approach.Here, we present an RAI platform that enables volumetric, single-pulse mapping of radiation dose deposition during FLASH-RTin vivo. The system utilizes a 16 × 16 ultrasound transducer matrix array with a model-based reconstruction algorithm to generate quantitative, three-dimensional dose maps with single pulse-level temporal resolution.Main results.In both water phantoms andin vivomurine models, RAI demonstrates high concordance with film dosimetry and TOPAS Monte Carlo simulations (3%/3 mm gamma index pass rates greater than 90% for small fields).Significance.This work establishes RAI as a viable technology for real-time, quantitative electron FLASH dosimetryin vivofor the first time, with the potential to support adaptive delivery, improve treatment safety, and facilitate the clinical translation of FLASH-RT.