Technical note: Flat panel proton radiography with a patient specific imaging field for accurate WEPL assessment

Oria, Carmen Seller; Free, Jeffrey; Marmitt, Gabriel Guterres; Knäusl, B.; Brandenburg, S.; Knopf, Antje; Meijers, Artürs; Langendijk, Johannes A.; Both, Stefan

doi:10.1002/mp.16208

Medical Physics

2023

DOI: 10.1002/mp.16208

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Technical note: Flat panel proton radiography with a patient specific imaging field for accurate WEPL assessment

Carmen Seller Oria

Jeffrey Free

Gabriel Guterres Marmitt

et al.

Abstract: Background: Proton radiography (PR) uses highly energetic proton beams to create images where energy loss is the main contrast mechanism. Waterequivalent path length (WEPL) measurements using flat panel PR (FP-PR) have potential for in vivo range verification. However, an accurate WEPL measurement via FP-PR requires irradiation with multiple energy layers, imposing high imaging doses. Purpose: A FP-PR method is proposed for accurate WEPL determination based on a patient-specific imaging field with a reduced nu… Show more

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2024

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Cited by 4 publications

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Development of a proton CT imaging system using scintillator‐based range detection

Liu,

Wang,

et al. 2024

Medical Physics

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BackgroundThe accuracy of proton therapy and preclinical proton irradiation experiments is susceptible to proton range uncertainties, which partly stem from the inaccurate conversion between CT numbers and relative stopping power (RSP). Proton computed tomography (PCT) can reduce these uncertainties by directly acquiring RSP maps.PurposeThis study aims to develop a novel PCT imaging system based on scintillator‐based proton range detection for accurate RSP reconstruction.MethodsThe proposed PCT system consists of a pencil‐beam brass collimator with a 1 mm aperture, an object stage capable of translation and 360° rotation, a plastic scintillator for dose‐to‐light conversion, and a complementary metal oxide semiconductor (CMOS) camera for light distribution acquisition. A calibration procedure based on Monte Carlo (MC) simulation was implemented to convert the obtained light ranges into water equivalent ranges. The water equivalent path lengths (WEPLs) of the imaged object were determined by calculating the differences in proton ranges obtained with and without the object in the beam path. To validate the WEPL calculation, measurements of WEPLs for eight tissue‐equivalent inserts were conducted. PCT imaging was performed on a custom‐designed phantom and a mouse, utilizing both 60 and 360 projections. The filtered back projection (FBP) algorithm was employed to reconstruct the RSP from WEPLs. Image quality was assessed based on the reconstructed RSP maps and compared to reference and simulation‐based reconstructions.ResultsThe differences between the calibrated and reference ranges of 110–150 MeV proton beams were within 0.18 mm. The WEPLs of eight tissue‐equivalent inserts were measured with accuracies better than 1%. Phantom experiments exhibited good agreement with reference and simulation‐based reconstructions, demonstrating average RSP errors of 1.26%, 1.38%, and 0.38% for images reconstructed with 60 projections, 60 projections after penalized weighted least‐squares algorithm denoising, and 360 projections, respectively. Mouse experiments provided clear observations of mouse contours and major tissue types. MC simulation estimated an imaging dose of 3.44 cGy for decent RSP reconstruction.ConclusionsThe proposed PCT imaging system enables RSP map acquisition with high accuracy and has the potential to improve dose calculation accuracy in proton therapy and preclinical proton irradiation experiments.

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Development of a proton CT imaging system using scintillator‐based range detection

Liu,

Wang,

et al. 2024

Medical Physics

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Integrated-mode proton radiography with 2D lateral projections

Simard,

Robertson,

Fullarton

et al. 2024

Phys. Med. Biol.

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Integrated-mode proton radiography leading to water equivalent thickness (WET) maps is an avenue of interest for motion management, patient positioning, and in vivo range verification. Radiographs can be obtained using a pencil beam scanning setup with a large 3D monolithic scintillator coupled with optical cameras. Established reconstruction methods either (1) involve a camera at the distal end of the scintillator, or (2) use a lateral view camera as a range telescope. Both approaches lead to limited image quality. The purpose of this work is to propose a third, novel reconstruction framework that exploits the 2D information provided by two lateral view cameras, to improve image quality achievable using lateral views. The three methods are first compared in a simulated Geant4 Monte Carlo framework using an extended cardiac torso (XCAT) phantom and a slanted edge. The proposed method with 2D lateral views is also compared with the range telescope approach using experimental data acquired with a plastic volumetric scintillator. Scanned phantoms include a Las Vegas (contrast), 9 tissue-substitute inserts (WET accuracy), and a paediatric head phantom. Resolution increases from 0.24 lp/mm (distal) to 0.33 lp/mm (proposed method) on the simulated slanted edge phantom, and the mean absolute error on WET maps of the XCAT phantom is reduced from 3.4 to 2.7 mm with the same methods. Experimental data from the proposed 2D lateral views indicate a 36\% increase in contrast relative to the range telescope method. High WET accuracy is obtained, with a mean absolute error of 0.4 mm over 9 inserts. Results are presented for various pencil beam spacing ranging from 2 to 6 mm. This work illustrates that high quality proton radiographs can be obtained with clinical beam settings and the proposed reconstruction framework with 2D lateral views, with potential applications in adaptive proton therapy.

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Energy painting: helium-beam radiography with thin detectors and multiple beam energies

Metzner,

Zhevachevska,

Schlechter

et al. 2024

Phys. Med. Biol.

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Abstract.Objective. Compact ion imaging systems based on thin detectors are a promising prospect for the clinical environment since they are easily integrated into the clinical workflow. Their measurement principle is based on energy deposition instead of the conventionally measured residual energy or range. Therefore, thin detectors are limited in the water-equivalent thickness range they can image with high precision. This article presents our energy painting method, which has been developed to render high precision imaging with thin detectors feasible even for objects with larger, clinically relevant WET ranges.Approach. A detection system exclusively based on pixelated silicon Timepix detectors was used at the Heidelberg ion-beam therapy center to track single helium ions and measure their energy deposition behind the imaged object. Calibration curves were established for five initial beam energies to relate the measured energy deposition to water-equivalent thickness (WET). They were evaluated regarding their accuracy, precision and temporal stability. Furthermore, a 60 mm × 12 mm region of a wedge phantom was imaged quantitatively exploiting the calibrated energies and five different mono-energetic images. These mono-energetic images were combined in a pixel-by-pixel manner by averaging the WET-data weighted according to their single-ion WET precision (SIWP) and the number of contributing ions.Main result. A quantitative helium-beam radiograph of the wedge phantom with an average SIWP of (1.82 ± 0.05) % over the entire WET interval from 150 mm to 220 mm was obtained. Compared to the previously used methodology, the SIWP improved by a factor of 2.49 ± 0.16. The relative stopping power value of the wedge derived from the energy-painted image matches the result from range pullback measurements with a relative deviation of only 0.4 %.Significance. The proposed method overcomes the insufficient precision for wide WET ranges when employing detection systems with thin detectors. Applying this method is an important prerequisite for imaging of patients. Hence, it advances detection systems based on energy deposition measurements towards clinical implementation.

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Technical note: Flat panel proton radiography with a patient specific imaging field for accurate WEPL assessment

Cited by 4 publications

References 49 publications

Development of a proton CT imaging system using scintillator‐based range detection

Development of a proton CT imaging system using scintillator‐based range detection

Integrated-mode proton radiography with 2D lateral projections

Energy painting: helium-beam radiography with thin detectors and multiple beam energies

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