Concept of proton radiography using energy resolved dose measurement

Bentefour, El Hassane; Schnuerer, Roland; Lu, Hsiao‐Ming

doi:10.1088/0031-9155/61/16/n386

Cited by 21 publications

(17 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We finally comment on the operating mode of the proton CT scanner: For both contrast mechanisms, operating a proton CT scanner in list-mode is demanding because the detection hardware needs to be extremely fast to keep up with the particle fluence of a therapeutic accelerator, even if operated at very low intensity (Johnson, 2018). As a technically simpler alternative, "integrated-mode" approaches have been studied for energy-loss proton CT and among them those where the imaged object is irradiated with pencil beams (Rescigno et al, 2015;Farace et al, 2016;Bentefour et al, 2016;Krah et al, 2018b) and the detector records the mean energy loss or residual range per pencil beam. In this sense, the averaging operation occurs physically as part of the detection process while it is done numerically during distance driven binning in list-mode operation.…”

Section: Discussionmentioning

confidence: 99%

Scattering proton CT

et al. 2020

View full text Add to dashboard Cite

Proton computed tomography (CT) is an imaging modality investigated mainly in the context of proton therapy as a complement to x-ray CT. It uses protons with high enough energy to fully traverse the imaged object. Common prototype systems measure each proton's position and direction upstream and downstream of the object as well as the energy loss which can be converted into the water equivalent thickness. A reconstruction algorithm then produces a map of the relative stopping power in the object. As an alternative to energy-loss proton CT, it has been proposed to reconstruct a map of the object's scattering power based on the protons' angular dispersion which can be estimated from the measured directions. As in energy-loss proton CT, reconstruction should best be performed considering the non-linear shape of proton trajectories due to multiple Coulomb scattering, but no algorithm to achieve this is so far available in the literature. In this work, we propose a filtered backprojection algorithm with distance-driven binning to account for the protons' most likely path. Furthermore, we present a systematic study of scattering proton CT in terms of inherent noise and spatial resolution and study the artefacts which arise from the physics of multiple Coulomb scattering. Our analysis is partly based on analytical models and partly on Monte Carlo simulations. Our results show that the proposed algorithm performs well in reconstructing relative scattering power maps, i.e. scattering power relative to that of water. Spatial resolution is improved by almost a factor of three compared to straight line projection and is comparable to energy-loss proton CT. Image noise, on the other hand, is inherently much higher. For example, in a water cylinder of 20 cm diameter, representative of a human head, noise in the central image pixel is about 40 times higher in scattering proton CT than in energy-loss proton CT. Relative scattering power in dense regions such as bone inserts is systematically underestimated by a few percent, depending on beam energy and phantom geometry.

show abstract

Section: Discussionmentioning

confidence: 99%

Scattering proton CT

et al. 2020

View full text Add to dashboard Cite

show abstract

“…This is realized due to the presence of the range modulator wheel which rotates at a fixed rotational speed, and thus dose rate profiles on the scale of the RMW cycle can be correlated to depth in medium. However, the same principles have been investigated for proton radiography in an active scanned beam delivery based on an energy‐resolved dose measurement methodology 17, 18…”

Section: Discussionmentioning

confidence: 99%

Time‐resolved diode dosimetry calibration through Monte Carlo modeling for in vivo passive scattered proton therapy range verification

Toltz

Hoesl

Schuemann

et al. 2017

J Applied Clin Med Phys

Self Cite

View full text Add to dashboard Cite

PurposeOur group previously introduced an in vivo proton range verification methodology in which a silicon diode array system is used to correlate the dose rate profile per range modulation wheel cycle of the detector signal to the water‐equivalent path length (WEPL) for passively scattered proton beam delivery. The implementation of this system requires a set of calibration data to establish a beam‐specific response to WEPL fit for the selected ‘scout’ beam (a 1 cm overshoot of the predicted detector depth with a dose of 4 cGy) in water‐equivalent plastic. This necessitates a separate set of measurements for every ‘scout’ beam that may be appropriate to the clinical case. The current study demonstrates the use of Monte Carlo simulations for calibration of the time‐resolved diode dosimetry technique.MethodsMeasurements for three ‘scout’ beams were compared against simulated detector response with Monte Carlo methods using the Tool for Particle Simulation (TOPAS). The ‘scout’ beams were then applied in the simulation environment to simulated water‐equivalent plastic, a CT of water‐equivalent plastic, and a patient CT data set to assess uncertainty.ResultsSimulated detector response in water‐equivalent plastic was validated against measurements for ‘scout’ spread out Bragg peaks of range 10 cm, 15 cm, and 21 cm (168 MeV, 177 MeV, and 210 MeV) to within 3.4 mm for all beams, and to within 1 mm in the region where the detector is expected to lie.ConclusionFeasibility has been shown for performing the calibration of the detector response for three ‘scout’ beams through simulation for the time‐resolved diode dosimetry technique in passive scattered proton delivery.

show abstract

“…The WEPL of proton beams can be obtained using energy-resolved dose functions (ERDFs), first proposed by Bentefour et al as a solution to measure WEPL by FP-PR with pencil beam scanning systems. An ERDF represents the change in the FP signal as a function of different initial pencil beam energies composing the PR field (Bentefour et al 2016). The WEPL can be retrieved by comparing the ERDFs obtained from a PR acquisition against a set of calibrated ERDFs with slabs of known water equivalent thickness (Bentefour et al 2016, Huo et al 2019, Alaka et al 2020, Harms et al 2020.…”

Section: Introductionmentioning

confidence: 99%

“…An ERDF represents the change in the FP signal as a function of different initial pencil beam energies composing the PR field (Bentefour et al 2016). The WEPL can be retrieved by comparing the ERDFs obtained from a PR acquisition against a set of calibrated ERDFs with slabs of known water equivalent thickness (Bentefour et al 2016, Huo et al 2019, Alaka et al 2020, Harms et al 2020.…”

Section: Introductionmentioning

confidence: 99%

Optimizing calibration settings for accurate water equivalent path length assessment using flat panel proton radiography

et al. 2021

View full text Add to dashboard Cite

Objective: Proton range uncertainties can compromise the effectiveness of proton therapy treatments. Water equivalent path length (WEPL) assessment by flat panel detector proton radiography (FP-PR) can provide means of range uncertainty detection. Since WEPL accuracy intrinsically relies on the FP-PR calibration parameters, the purpose of this study is to establish an optimal calibration procedure that ensures high accuracy of WEPL measurements. To that end, several calibration settings were investigated. Approach: FP-PR calibration datasets were obtained simulating PR fields with different proton energies, directed towards water-equivalent material slabs of increasing thickness. The parameters investigated were the spacing between energy layers (ΔE) and the increment in thickness of the water-equivalent material slabs (ΔX) used for calibration. 30 calibrations were simulated, as a result of combining ΔE=9, 7, 5, 3, 1 MeV and ΔX=10, 8, 5, 3, 2, 1 mm. FP-PRs through a CIRS electron density phantom were simulated, and WEPL images corresponding to each calibration were obtained. Ground truth WEPL values were provided by range probing multi-layer ionization chamber simulations on each insert of the phantom. Relative WEPL errors between FP-PR simulations and ground truth were calculated for each insert. Mean relative WEPL errors and standard deviations across all inserts were computed for WEPL images obtained with each calibration. Main results: Large mean and standard deviations were found in WEPL images obtained with large ΔE values (ΔE=9 or 7 MeV), for any ΔX. WEPL images obtained with ΔE5 MeV and ΔX5 mm resulted in a WEPL accuracy with mean values within ±0.5% and standard deviations around 1%. Significance: An optimal FP calibration in the framework of this study was established, characterized by 3 MeVΔE5 MeV and 2 mmΔX5 mm. Within these boundaries, highly accurate WEPL acquisitions using FP-PR are feasible and practical, holding the potential to assist future online range verification quality control procedures.

show abstract

Concept of proton radiography using energy resolved dose measurement

Cited by 21 publications

References 19 publications

Scattering proton CT

Scattering proton CT

Time‐resolved diode dosimetry calibration through Monte Carlo modeling for in vivo passive scattered proton therapy range verification

Optimizing calibration settings for accurate water equivalent path length assessment using flat panel proton radiography

Contact Info

Product

Resources

About