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

Lascaud, Julie; Dash, Pratik; Wieser, Hans-Peter; Kalunga, Ronaldo; Würl, Matthias; Assmann, W.; Parodi, Katia

doi:10.1088/1361-6560/ac215e

Cited by 15 publications

(34 citation statements)

References 35 publications

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“…The small footprint of hydrophone is also desirable for reducing the spatial averaging effect. 20 However, because the frequency range of IA waves is relatively low (< 100 kHz), the thickness of piezoelectric ceramics tends to be large. Moreover, the active area of hydrophones needs to be large to increase the SNR which could further increase the detector size.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2023

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Background Proton range uncertainty has been the main factor limiting the ability of proton therapy to concentrate doses to tumors to their full potential. Ionoacoustic (IA) range verification is an approach to reducing this uncertainty by detecting thermoacoustic waves emitted from an irradiated volume immediately following a pulsed proton beam delivery; however, the signal weakness has been an obstacle to its clinical application. To increase the signal‐to‐noise ratio (SNR) with the conventional piezoelectric hydrophone (PH), the detector‐sensitive volume needs to be large, but it could narrow the range of available beam angles and disturb real‐time images obtained during beam delivery. Purpose To prevent this issue, we investigated a millimeter‐sized optical hydrophone (OH) that exploits the laser interferometric principle. For two types of IA waves [γ‐wave emitted from the Bragg peak (BP) and a spherical IA wave with resonant frequency (SPIRE) emitted from the gold fiducial marker (GM)], comparisons were made with PH in terms of waveforms, SNR, range detection accuracy, and signal intensity robustness against the small detector misalignment, particularly for SPIRE. Methods A 100‐MeV proton beam with a 27 ns pulse width and 4 mm beam size was produced using a fixed‐field alternating gradient accelerator and was irradiated to the water phantom. The GM was set on the beam's central axis. Acrylic plates of various thicknesses, up to 12 mm, were set in front of the phantoms to shift the proton range. OH was set distal and lateral to the beam, and the range was estimated using the time‐of‐flight method for γ‐wave and by comparing with the calibration data (SPIRE intensity versus the distance between the GM and BP) derived from an IA wave transport simulation for SPIRE. The BP dose per pulse was 0.5–0.6 Gy. To measure the variation in SPIRE amplitude against the hydrophone misalignment, the hydrophone was shifted by ± 2 mm at a maximum in lateral directions. Results Despite its small size, OH could detect γ‐wave with a higher SNR than the conventional PH (diameter, 29 mm), and a single measurement was sufficient to detect the beam range with a submillimeter accuracy in water. In the SPIRE measurement, OH was far more robust against the detector misalignment than the focused PH (FPH) used in our previous study [5%/mm (OH) versus 80%/mm (FPH)], and the correlation between the measured SPIRE intensity and the distance between the GM and BP agreed well with the simulation results. However, the OH sensitivity was lower than the FPH sensitivity, and about 5.6‐Gy dose was required to decrease the intensity variation among measurements to less than 10%. Conclusion The miniature OH was found to detect weak IA signals produced by proton beams with a BP dose used in hypofractionated regimens. The OH sensitivity improvement at the MHz regime is worth exploring as the next step.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2023

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“…To advance preclinical proton therapy research, the SIRMIO project [1] (small-animal proton irradiator for research in molecular image-guided radiation-oncology) aims to build a smallanimal proton irradiator equipped with a dedicated beamline to produce a focused, narrow proton beam (σ ≈ 1 mm) with energies from 20 MeV to 50 MeV to irradiate small animals [2]. Imaging for tumor detection, treatment planning, and positioning will be provided by co-registered ultrasound [3] and proton imaging, with the advantage that proton radiography will directly provide the waterequivalent thickness (WET) and proton computed tomography (pCT), the relative (to water) stopping power (RSP) needed for treatment planning [4][5][6]. Ionoacoustic measurements [3] and an in-beam PET system [7] are used for in vivo range verification.…”

Section: Introductionmentioning

confidence: 99%

“…Imaging for tumor detection, treatment planning, and positioning will be provided by co-registered ultrasound [3] and proton imaging, with the advantage that proton radiography will directly provide the waterequivalent thickness (WET) and proton computed tomography (pCT), the relative (to water) stopping power (RSP) needed for treatment planning [4][5][6]. Ionoacoustic measurements [3] and an in-beam PET system [7] are used for in vivo range verification.…”

Section: Introductionmentioning

confidence: 99%

Development of integration mode proton imaging with a single CMOS detector for a small animal irradiation platform

et al. 2023

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A novel irradiation platform for preclinical proton therapy studies foresees proton imaging for accurate setup and treatment planning. Imaging at modern synchrocyclotron-based proton therapy centers with high instantaneous particle flux is possible with an integration mode setup. The aim of this work is to determine an object’s water-equivalent thickness (WET) with a commercially available large-area CMOS sensor. Image contrast is achieved by recording the proton energy deposition in detector pixels for several incoming beam energies (here, called probing energies) and applying a signal decomposition method that retrieves the water-equivalent thickness. A single planar 114 mm × 65 mm CMOS sensor (49.5 µm pixel pitch) was used for this study, aimed at small-animal imaging. In experimental campaigns, at two isochronous cyclotron-based facilities, probing energies suitable for small-animal-sized objects were produced once with built-in energy layer switching and the other time, using a custom degrader wheel. To assess water-equivalent thickness accuracy, a micro-CT calibration phantom with 10 inserts of tissue-mimicking materials was imaged at three phantom-to-detector distances: 3 mm, 13 mm, and 33 mm. For 3 mm and 13 mm phantom-to-detector distance, the average water-equivalent thickness error compared to the ground truth was about 1% and the spatial resolution was 0.16(3) mm and 0.47(2) mm, respectively. For the largest separation distance of 33 mm air gap, proton scattering had considerable impact and the water-equivalent thickness relative error increased to 30%, and the spatial resolution was larger than 1.75 mm. We conclude that a pixelated CMOS detector with dedicated post-processing methods can enable fast proton radiographic imaging in a simple and compact setup for small-animal-sized objects with high water-equivalent thickness accuracy and spatial resolution for reasonable phantom-to-detector distances.

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“…1,2 The aim is to detect and compensate range shifts that originate from uncertainties in imaging, planning, patient setup, anatomical changes, etc. In addition to the existing approaches such as PET, 3 prompt gamma, 4 and ionoacoustics, 5 Albert et al 6 proposed to detect the electric field of the primary protons. Subsequently, we further developed their analytical method to characterize the complete electromagnetic signal generated by a proton beam in different tissues.…”

Section: Introductionmentioning

confidence: 99%

“…The aim is to detect and compensate range shifts that originate from uncertainties in imaging, planning, patient setup, anatomical changes, etc. In addition to the existing approaches such as PET, 3 prompt gamma, 4 and ionoacoustics, 5 Albert et al 6 . proposed to detect the electric field of the primary protons.…”

Section: Introductionmentioning

confidence: 99%

Impact of secondary particles on the magnetic field generated by a proton pencil beam: a finite‐element analysis based on Geant4‐DNA simulations

et al. 2023

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Purpose To investigate the static magnetic field generated by a proton pencil beam as a candidate for range verification by means of Monte Carlo simulations, thereby improving upon existing analytical calculations. We focus on the impact of statistical current fluctuations and secondary protons and electrons. Methods We considered a pulsed beam (10 μ${\umu}$s pulse duration) during the duty cycle with a peak beam current of 0.2 μ$\umu$A and an initial energy of 100 MeV. We ran Geant4‐DNA Monte Carlo simulations of a proton pencil beam in water and extracted independent particle phase spaces. We calculated longitudinal and radial current density of protons and electrons, serving as an input for a magnetic field estimation based on a finite element analysis in a cylindrical geometry. We made sure to allow for non‐solenoidal current densities as is the case of a stopping proton beam. Results The rising proton charge density toward the range is not perturbed by energy straggling and only lowered through nuclear reactions by up to 15%, leading to an approximately constant longitudinal current. Their relative low density however (at most 0.37 protons/mm3 for the 0.2 μ${\umu}$A current and a beam cross‐section of 2.5 mm), gives rise to considerable current density fluctuations. The radial proton current resulting from lateral scattering and being two orders of magnitude weaker than the longitudinal current is subject to even stronger fluctuations. Secondary electrons with energies above 10 eV, that far outnumber the primary protons, reduce the primary proton current by only 10% due to their largely isotropic flow. A small fraction of electrons (<1%), undergoing head‐on collisions, constitutes the relevant electron current. In the far‐field, both contributions to the magnetic field strength (longitudinal and lateral) are independent of the beam spot size. We also find that the nuclear reaction‐related losses cause a shift of 1.3 mm to the magnetic field profile relative to the actual range, which is further enlarged to 2.4 mm by the electron current (at a distance of ρ=50$\rho =50$ mm away from the central beam axis). For ρ>45$\rho >45$ mm, the shift increases linearly. While the current density variations cause significant magnetic field uncertainty close to the central beam axis with a relative standard deviation (RSD) close to 100%, they average out at a distance of 10 cm, where the RSD of the total magnetic field drops below 2%. Conclusions With the small influence of the secondary electrons together with the low RSD, our analysis encourages an experimental detection of the magnetic field through sensitive instrumentation, such as optical magnetometry or SQUIDs.

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

Cited by 15 publications

References 35 publications

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

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

Development of integration mode proton imaging with a single CMOS detector for a small animal irradiation platform

Impact of secondary particles on the magnetic field generated by a proton pencil beam: a finite‐element analysis based on Geant4‐DNA simulations

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