Feasibility study of 3D time‐reversal reconstruction of proton‐induced acoustic signals for dose verification in the head and the liver: A simulation study.

Purpose: In vivo range and dose verification based on proton‐induced acoustics (protoacoustics) is potentially a useful tool for proton therapy. Built upon our previous study with two‐dimensional reconstruction, the time reversal (TR) method was extended to three‐dimensional (3D) and evaluated at two treatment sites (head and liver) through simulation, with the emphasis on a number of aspects such as increased spatial coverage, computational workload, and signal interference among slices. Methods: Two mono‐energetic pencil beams were modeled in each site. The k‐Wave toolbox was used to investigate the propagation and TR reconstruction of acoustic waves. The performance was quantitatively assessed based on mean square error (MSE) for dose verification and Bragg peak localization error (ΔBP) for range verification, with regard to five parameters: number of sensors, sampling duration, sampling timestep, spill time, and noise level. Results: The respective impacts of five parameters are examined. Under the optimum setting, the achievable ΔBP can be limited within 1 voxel (voxel size: 3 × 3 × 3 mm3) and the achievable MSE can be limited below 0.02, for the head case (56 sensors) and the liver case (204 sensors), respectively. Conclusions: The feasibility of range and dose verification utilizing the 3D TR method is demonstrated, as the very first step. In spite of several challenges unique to the 3D case (spatial coverage, computational workload, and signal interference among slices, etc.), promising performance is found and can be further improved through optimizing the deployment of sensors. The proposed approach may find potential use in several applications: beam diagnostics, in vivo dosimetry, and treatment monitoring. [ABSTRACT FROM AUTHOR]