Fast range measurement of spot scanning proton beams using a volumetric liquid scintillator detector

Hui, Cheukkai; Robertson, Daniel; Alsanea, Fahed; Beddar, Sam

doi:10.1088/2057-1976/1/2/025204

Cited by 11 publications

(8 citation statements)

References 17 publications

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“…The line profile across the acrylic phantom provided the full-width at half maximum (2.78 cm) value that is close to the physical diameter (2.8 cm) of the acrylic insert. The smooth edges of the line profiles were likely due to cone beam projection of the inserts resulting from a combination of proton beam divergence (2.12°, for a 10 cm 2 field area formed by beam source placed 270 cm away from the isocenter plane), as suggested by Tanaka et al (2016), and from camera system divergence (Hui et al 2015).…”

Section: Resultsmentioning

confidence: 99%

A proton imaging system using a volumetric liquid scintillator: a preliminary study

Darne

Alsanea

Robertson

et al. 2019

Biomed. Phys. Eng. Express

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With the expansion of proton radiotherapy for cancer treatments, it has become important to explore proton-based imaging technologies to increase the accuracy of proton treatment planning, alignment, and verification. The purpose of this study is to demonstrate the feasibility of using a volumetric liquid scintillator to generate proton radiographs at a clinically relevant energy (180 MeV) using an integrating detector approach. The volumetric scintillator detector is capable of capturing a wide distribution of residual proton beam energies from a single beam irradiation. It has the potential to reduce acquisition time and imaging dose compared to other proton radiography methods. The imaging system design is comprised of a volumetric (20 × 20 × 20 cm 3 ) organic liquid scintillator working as a residual-range detector and a charge-coupled device (CCD) placed along the beams'-eye-view for capturing radiographic projections. The scintillation light produced within the scintillator volume in response to a 3-dimensional distribution of residual proton beam energies is captured by the CCD as a 2-dimensional grayscale image. A light intensity-to-water equivalent thickness (WET) curve provided WET values based on measured light intensities. The imaging properties of the system, including its contrast, signal-to-noise ratio, and spatial resolution (0.19 line-pairs/mm) were determined. WET values for selected Gammex phantom inserts including solid water, acrylic, and cortical bone were calculated from the radiographs with a relative accuracy of −0.82%, 0.91%, and −2.43%, respectively. Image blurring introduced by system optics was accounted for, resulting in sharper image features. Finally, the system's ability to reconstruct proton CT images from radiographic projections was demonstrated

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Section: Resultsmentioning

confidence: 99%

A proton imaging system using a volumetric liquid scintillator: a preliminary study

Darne

Alsanea

Robertson

et al. 2019

Biomed. Phys. Eng. Express

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“…Robertson et al used simulated three‐dimensional LET distributions and Birks’ model to correct for quenching effects in measured proton PDL curves. This correction was then used for fast measurements of the range of proton pencil beams . It relies on the accurate matching of the predicted and the measured LET distributions and is therefore prone to small shifts between the simulated and the measured Bragg curve .…”

Section: Introductionmentioning

confidence: 99%

“…This correction was then used for fast measurements of the range of proton pencil beams. 22 It relies on the accurate matching of the predicted and the measured LET distributions and is therefore prone to small shifts between the simulated and the measured Bragg curve. 1,23 Range information has also been extracted from the scintillation light output without applying any correction for quenching at all.…”

Section: Introductionmentioning

confidence: 99%

A mathematical expression for depth‐light curves of therapeutic proton beams in a quenching scintillator

Kelleter

Jolly

2020

Medical Physics

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Purpose: Recently, there has been increasing interest in the development of scintillator-based detectors for the measurement of depth-dose curves of therapeutic proton beams (Beaulieu and Beddar [2016], Phys Med Biol., 61:R305-R343). These detectors allow the measurement of single beam parameters such as the proton range or the reconstruction of the full three-dimensional dose distribution. Thus, scintillation detectors could play an important role in beam quality assurance, online beam monitoring, and proton imaging. However, the light output of the scintillator as a function of dose deposition is subject to quenching effects due to the high-specific energy loss of incident protons, particularly in the Bragg peak. The aim of this work is to develop a model that describes the percent depth-light curve in a quenching scintillator and allow the extraction of information about the beam range and the strength of the quenching. Methods: A mathematical expression of a depth-light curve, derived from a combination of Birks' law (Birks [1951], Proc Phys Soc A., 64:874) and Bortfeld's Bragg curve (Bortfeld [1997], Med Phys., 24:2024-2033) that is termed a "quenched Bragg" curve, is presented. The model is validated against simulation and measurement. Results: A fit of the quenched Bragg model to simulated depth-light curves in a polystyrene-based scintillator shows good agreement between the two, with a maximum deviation of 2.5% at the Bragg peak. The differences are larger behind the Bragg peak and in the dose build-up region. In the same simulation, the difference between the reconstructed range and the reference proton range is found to be always smaller than 0.16 mm. The comparison with measured data shows that the fitted beam range agrees with the reference range within their respective uncertainties. Conclusions: The quenched Bragg model is, therefore, an accurate tool for the range measurement from quenched depth-dose curves. Moreover, it allows the reconstruction of the beam energy spread, the particle fluence, and the magnitude of the quenching effect from a measured depth-light curve.

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“…However, film is not efficient for a frequent constancy check of ranges for multiple proton energies because of postprocessing requirements and the number of films required. Volumetric scintillator detectors have also been used for fast range verification in proton therapy, and a few recent studies reported that sub‐millimeter accuracy was achieved, but this is not currently a commercially available technology.…”

Section: Introductionmentioning

confidence: 99%

A novel and fast method for proton range verification using a step wedge and 2D scintillator

et al. 2017

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Purpose: To implement and evaluate a novel and fast method for proton range verification by using a planar scintillator and step wedge. Methods: A homogenous proton pencil beam plan with 35 energies was designed and delivered to a 2D flat scintillator with a step wedge. The measurement was repeated 15 times (3 different days, 5 times per day). The scintillator image was smoothed, the Bragg peak and distal fall off regions were fitted by an analytical equation, and the proton range was calculated using simple trigonometry. The accuracy of this method was verified by comparing the measured ranges to those obtained using an ionization chamber and a scanning water tank, the gold standard. The reproducibility was evaluated by comparing the ranges over 15 repeated measurements. The sensitivity was evaluated by delivering to same beam to the system with a film inserted under the wedge. Results: The range accuracy of all 35 proton energies measured over 3 days was within 0.2 mm. The reproducibility in 15 repeated measurements for all 35 proton ranges was AE0.045 mm. The sensitivity to range variation is 0.1 mm for the worst case. This efficient procedure permits measurement of 35 proton ranges in less than 3 min. The automated data processing produces results immediately. The setup of this system took less than 5 min. The time saving by this new method is about two orders of magnitude when compared with the time for water tank range measurements. Conclusions: A novel method using a scintillator with a step wedge to measure the proton range was implemented and evaluated. This novel method is fast and sensitive, and the proton range measured by this method was accurate and highly reproducible.

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Fast range measurement of spot scanning proton beams using a volumetric liquid scintillator detector

Cited by 11 publications

References 17 publications

A proton imaging system using a volumetric liquid scintillator: a preliminary study

A proton imaging system using a volumetric liquid scintillator: a preliminary study

A mathematical expression for depth‐light curves of therapeutic proton beams in a quenching scintillator

A novel and fast method for proton range verification using a step wedge and 2D scintillator

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