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

Abstract

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.

Investigating the accuracy of co-registered ionoacoustic and ultrasound images in pulsed proton beams

“…Therefore, the BP position and relative dose can be inferred from the reconstruction of the initial pressure, whereas the absolute dose reconstruction requires an accurate knowledge of the medium properties (density and Grünensein parameter). Recent simulation studies have investigated the accuracy of ionoacoustics-based dose reconstruction for clinical scenarios using a linear array (van Dongen et al 2019) or sparse two and three dimensional sensor arrays positioned around the patient (Yu et al 2019(Yu et al , 2021. Assuming exact knowledge of the medium, they showed that the BP can be located with millimeter or sub-millimeter accuracy, depending on the proton pulse time profile.…”

Ionoacoustic application of an optical hydrophone to detect proton beam range in water

“…Moreover, the accuracy will be increased if we create a dictionary of IA waves before the treatment to match the measured signals 22,31 . The use of multiple (or array‐type) sensors will further increase the accuracy as the three‐dimensional dose distributions can be obtained using iterative time‐reversal reconstruction methods 20,32,33,34 . Particularly, a novel array OH sensor reported by van der Heiden et al 52 .…”

“…22,31 The use of multiple (or array-type) sensors will further increase the accuracy as the three-dimensional dose distributions can be obtained using iterative time-reversal reconstruction methods. 20,32,33,34 Particularly, a novel array OH sensor reported by van der Heiden et al 52 is expected to realize the very accurate localization of BP with a minimal footprint. This line of research will significantly enhance the possibility of realizing IA range verification in clinics.…”

“…Because hydrophones must be placed on a patient's surface, the detector should be as small as possible to avoid narrowing the range of available beam angles and disturbing the real‐time images during beam delivery such as in X‐ray fluoroscopy. In fact, several researchers proposed the use of multiple detectors (from four to more than 200) to increase the estimated range reliability and/or to reconstruct dose distributions 31–35 . When these techniques are used, the range of available beam angles that do not overlap with the detectors may be reduced as the detector size becomes larger.…”

“…In fact, several researchers proposed the use of multiple detectors (from four to more than 200) to increase the estimated range reliability and/or to reconstruct dose distributions. [31][32][33][34][35] When these techniques are used, the range of available beam angles that do not overlap with the detectors may be reduced as the detector size becomes larger. In addition, PH could make larger shadows in the fluoroscopy images compared to the OH (see Figure S1 in the Supplemental Material), indicating that when these devices are used for range verification during the treatment of respiratory-moving tumors, it can be an obstacle to tracking tumors or fiducial markers when the projected images of hydrophones overlap with the images of tumors or markers.…”