Single pulse protoacoustic range verification using a clinical synchrocyclotron

Abstract

Objective: Proton therapy as the next generation radiation-based cancer therapy offers dominant advantages over conventional radiation therapy due to the utilization of the Bragg peak; however, range uncertainty in beam delivery substantially mitigates the advantages of proton therapy. This work reports using protoacoustic measurements to determine the location of proton Bragg peak deposition within a water phantom in real time during beam delivery. Approach: In protoacoustics, proton beams have a definitive range, depositing a majority of the dose at the Bragg peak; this dose is then converted to heat. The resulting thermoelastic expansion generates a 3D acoustic wave, which can be detected by acoustic detectors to localize the Bragg peak. Main results: Protoacoustic measurements were performed with a synchrocyclotron proton machine over the exhaustive energy range from 45.5MeV to 227.15MeV in clinic. It was found that the amplitude of the acoustic waves is proportional to proton dose deposition, and therefore encodes dosimetric information. With the guidance of protoacoustics, each individual proton beam (7pC/pulse) can be directly visualized with sub-millimeter (<0.7 mm) resolution using single beam pulse for the first time. Significance: The ability to localize the Bragg peak in real-time and obtain acoustic signals proportional to dose within tumors could enable precision proton therapy and hope to progress towards in-vivo measurements.

Range verification of a clinical proton beam in an abdominal phantom by co-registration of ionoacoustics and ultrasound

“…The comparability with the cited studies is only valid to a limited extent due to differences in the experimental design. In particular, it must be mentioned that the studies (Sueyasu et al 2022) and (Caron et al 2023) both use a water phantom and a substantially higher beam current (more than 4-fold) than in this study. It has already been shown that a higher instantaneous beam current contributes to a higher SNR at the same number of protons or dose (Schauer et al 2022), respectively.…”

“…Analysing the time of flight of the ionoacoustic signal propagation allows conclusions to be drawn about the position of the Bragg peak. Since the ionoacoustic signal is typically very noisy at clinically relevant doses, the signals are often averaged and filtered with analogue and digital filters such as band-pass filters, SavitzkyGolay filters (Caron et al 2023) or wavelet filters (Vallicelli et al 2021). From the time dependent ionoacoustic signal the location and the shape of the dose deposition can in theory be retrieved using a deconvolution procedure, however as deconvolution is a noise-sensitive process, this method is limited to high quality signals.…”

“…In recent studies from 2022 (Sueyasu et al 2022) and 2023 (Caron et al 2023), ionoacoustic signals could even be measured from single pulses using an optical hydrophone and/or piezoelectric ones (Olympus V389-SU (Caron et al 2023), Olympus V391-SU (Sueyasu et al 2022)). The comparability with the cited studies is only valid to a limited extent due to differences in the experimental design.…”

Ionic-resolution protoacoustic microscopy: A feasibility study

“…For pulsed clinical proton machines ($100-250 MeV protons and $ls pulse duration), generation and sensing of protoacoustic waves has been reported by several groups across the globe. 28,30,46 Protoacoustic signals generated from $20 MeV protons with 200 ns pulse duration have also been reported. 47 Laser-driven proton beams are known to have the pulse durations of a few picoseconds [43][44][45] and are expected to be more suitable for PrAM as they easily satisfy the stress and thermal confinement conditions.…”

“…When pulsed proton radiation is absorbed by tissues, it triggers the generation of protoacoustic waves resulting from the thermoelastic expansion of the irradiated tissue. These protoacoustic waves have been detected by numerous research groups worldwide [28][29][30][31][32] and are now being employed for on-line range verification and dose monitoring during the treatment. The propagation of protoacoustic waves in an acoustically homogeneous medium follows the acoustic wave propagation equation, 33…”