Dictionary-based protoacoustic dose map imaging for proton range verification

Freijo, Clara; Herraiz, Joaquín L.; Sánchez-Parcerisa, Daniel; Udías, J. M.

doi:10.1016/j.pacs.2021.100240

Cited by 16 publications

(12 citation statements)

References 51 publications

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“…In addition, array transducers may be used to estimate the in vivo sound speed for the liver 36 and breast, 37 increasing the accuracy of in vivo range verification. Methods that utilize multiple hydrophones simultaneously to reconstruct the dose distribution were also explored in simulation study, using 3D filtered backprojection, 38 time reversal algorithms, 39 and dictionary method 40 . Such lines of approach may be more suitable for heterogeneous tissues in clinical settings.…”

Section: Discussionmentioning

confidence: 99%

Technical Note: Range verification of pulsed proton beams from fixed‐field alternating gradient accelerator by means of time‐of‐flight measurement of ionoacoustic waves

et al. 2021

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Purpose Ionoacoustics is one of the promising approaches to verify the beam range in proton therapy. However, the weakness of the wave signal remains a main hindrance to its application in clinics. Here we studied the potential use of a fixed‐field alternating gradient accelerator (FFA), one of the accelerator candidates for future proton therapy. For such end, magnitude of the pressure wave and range accuracy achieved by the short‐pulsed beam of FFA were assessed, using both simulation and experimental procedure. Methods A 100 MeV proton beam from the FFA was applied on a water phantom, through the acrylic wall. The beam range measured by the Bragg peak (BP)‐ionization chamber (BPC) was 77.6 mm, while the maximum dose at BP was estimated to be 0.35 Gy/pulse. A hydrophone was placed 20 mm downstream of the BP, and signals were amplified and stored by a digital oscilloscope, averaged, and low‐pass filtered. Time‐of‐flight (TOF) and two relative TOF values were analyzed in order to determine the beam range. Furthermore, an acoustic wave transport simulation was conducted to estimate the amplitude of the pressure waves. Results The range calculated when using two relative TOF was 78.16 ± 0.01 and 78.14 ± 0.01 mm, respectively, both values being coherent with the range measured by the BPC (the difference was 0.5‒0.6 mm). In contrast, utilizing the direct TOF resulted in a range error of 1.8 mm. Fivefold and 50‐fold averaging were required to suppress the range variation to below 1 mm for TOF and relative TOF measures, respectively. The simulation suggested the magnitude of pressure wave at the detector exceeded 7 Pascal. Conclusion A submillimeter range accuracy was attained with a pulsed beam of about 21 ns from an FFA, at a clinical energy using relative TOF. To precisely quantify the range with a single TOF measurement, subsequent improvement in the measuring system is required.

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Section: Discussionmentioning

confidence: 99%

Technical Note: Range verification of pulsed proton beams from fixed‐field alternating gradient accelerator by means of time‐of‐flight measurement of ionoacoustic waves

et al. 2021

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“…In more realistic situations, tissue heterogeneity in patients will distort the IA waves, and more sophisticated methods, such as the coregistration of IA signals and ultrasound echo images, may be required to precisely localize the BP position 20,22,23,51 . 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 .…”

Section: Discussionmentioning

confidence: 99%

“…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.…”

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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“…Another realistic approach looking into the clinical application is to establish a database of signals, to serve as a template for the denoising procedure. A recent study established a dictionary of simulated signals obtained for different detector positions which were then used for a denoising procedure ( 31 ). However, without dose limitations, accurate templates could be generated experimentally including information on the proton pulse shape and characteristic transducer responses.…”

Section: Discussionmentioning

confidence: 99%

Proton beam range verification by means of ionoacoustic measurements at clinically relevant doses using a correlation-based evaluation

et al. 2022

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PurposeThe Bragg peak located at the end of the ion beam range is one of the main advantages of ion beam therapy compared to X-Ray radiotherapy. However, verifying the exact position of the Bragg peak within the patient online is a major challenge. The goal of this work was to achieve submillimeter proton beam range verification for pulsed proton beams of an energy of up to 220 MeV using ionoacoustics for a clinically relevant dose deposition of typically 2 Gy per fraction by i) using optimal proton beam characteristics for ionoacoustic signal generation and ii) improved signal detection by correlating the signal with simulated filter templates.MethodsA water tank was irradiated with a preclinical 20 MeV proton beam using different pulse durations ranging from 50 ns up to 1 μs in order to maximise the signal-to-noise ratio (SNR) of ionoacoustic signals. The ionoacoustic signals were measured using a piezo-electric ultrasound transducer in the MHz frequency range. The signals were filtered using a cross correlation-based signal processing algorithm utilizing simulated templates, which enhances the SNR of the recorded signals. The range of the protons is evaluated by extracting the time of flight (ToF) of the ionoacoustic signals and compared to simulations from a Monte Carlo dose engine (FLUKA).ResultsOptimised SNR of 28.0 ± 10.6 is obtained at a beam current of 4.5 μA and a pulse duration of 130 ns at a total peak dose deposition of 0.5 Gy. Evaluated ranges coincide with Monte Carlo simulations better than 0.1 mm at an absolute range of 4.21 mm. Higher beam energies require longer proton pulse durations for optimised signal generation. Using the correlation-based post-processing filter a SNR of 17.8 ± 5.5 is obtained for 220 MeV protons at a total peak dose deposition of 1.3 Gy. For this clinically relevant dose deposition and proton beam energy, submillimeter range verification was achieved at an absolute range of 303 mm in water.ConclusionOptimal proton pulse durations ensure an ideal trade-off between maximising the ionoacoustic amplitude and minimising dose deposition. In combination with a correlation-based post-processing evaluation algorithm, a reasonable SNR can be achieved at low dose levels putting clinical applications for online proton or ion beam range verification into reach.

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Dictionary-based protoacoustic dose map imaging for proton range verification

Cited by 16 publications

References 51 publications

Technical Note: Range verification of pulsed proton beams from fixed‐field alternating gradient accelerator by means of time‐of‐flight measurement of ionoacoustic waves

Technical Note: Range verification of pulsed proton beams from fixed‐field alternating gradient accelerator by means of time‐of‐flight measurement of ionoacoustic waves

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

Proton beam range verification by means of ionoacoustic measurements at clinically relevant doses using a correlation-based evaluation

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