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Krah N, Dauvergne D, Létang JM, Rit S, Testa É. Relative stopping power resolution in time-of-flight proton CT. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac7191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 05/19/2022] [Indexed: 11/11/2022]
Abstract
Abstract
Objective. Proton computed tomography (CT) is similar to x-ray CT but relies on protons rather than photons to form an image. In its most common operation mode, the measured quantity is the amount of energy that a proton has lost while traversing the imaged object from which a relative stopping power map can be obtained via tomographic reconstruction. To this end, a calorimeter which measures the energy deposited by protons downstream of the scanned object has been studied or implemented as energy detector in several proton CT prototypes. An alternative method is to measure the proton’s residual velocity and thus its kinetic energy via the time of flight (TOF) between at least two sensor planes. In this work, we study the RSP resolution, seen as image noise, which can be expected from TOF proton CT systems.
Approach. We rely on physics models on the one hand and statistical models of the relevant uncertainties on the other to derive closed form expressions for the noise in projection images. The TOF measurement error scales with the distance between the TOF sensor planes and is reported as velocity error in ps/m. We use variance reconstruction to obtain noise maps of a water cylinder phantom given the scanner characteristics and additionally reconstruct noise maps for a calorimeter-based proton CT system as reference. We use Monte Carlo simulations to verify our model and to estimate the noise due to multiple Coulomb scattering inside the object. We also provide a comparison of TOF helium and proton CT.
Main results. We find that TOF proton CT with 30 ps m−1 velocity error reaches similar image noise as a calorimeter-based proton CT system with 1% energy error (1 sigma error). A TOF proton CT system with a 50 ps m−1 velocity error produces slightly less noise than a 2% calorimeter system. Noise in a reconstructed TOF proton CT image is spatially inhomogeneous with a marked increase towards the object periphery. Our modelled noise was consistent with Monte Carlo simulated images. TOF helium CT offers lower RSP noise at equal fluence, but is less advantageous at equal imaging dose.
Significance. This systematic study of image noise in TOF proton CT can serve as a guide for future developments of this alternative solution for estimating the residual energy of protons and helium ions after the scanned object.
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Ulrich-Pur F, Bergauer T, Burker A, Hirtl A, Irmler C, Kaser S, Pitters F, Rit S. Feasibility study of a proton CT system based on 4D-tracking and residual energy determination via time-of-flight. Phys Med Biol 2022; 67. [PMID: 35354129 DOI: 10.1088/1361-6560/ac628b] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 03/30/2022] [Indexed: 11/12/2022]
Abstract
Objective.For dose calculations in ion beam therapy, it is vital to accurately determine the relative stopping power (RSP) distribution within the treatment volume. A suitable imaging modality to achieve the required RSP accuracy is proton computed tomography (pCT), which usually uses a tracking system and a separate residual energy (or range) detector to directly measure the RSP distribution. This work investigates the potential of a novel pCT system based on a single detector technology, namely low gain avalanche detectors (LGADs). LGADs are fast 4D-tracking detectors, which can be used to simultaneously measure the particle position and time with precise timing and spatial resolution. In contrast to standard pCT systems, the residual energy is determined via a time-of-flight (TOF) measurement between different 4D-tracking stations.Approach.To show the potential of using 4D-tracking for proton imaging, we studied and optimized the design parameters for a realistic TOF-pCT system using Monte Carlo simulations. We calculated the RSP accuracy and RSP resolution inside the inserts of the CTP404 phantom and compared the results to a simulation of an ideal pCT system.Main results.After introducing a dedicated calibration procedure for the TOF calorimeter, RSP accuracies less than 0.6% could be achieved. We also identified the design parameters with the strongest impact on the RSP resolution and proposed a strategy to further improve the image quality.Significance.This comprehensive study of the most important design aspects for a novel TOF-pCT system could help guide future hardware developments and, once implemented, improve the quality of treatment planning in ion beam therapy.
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Affiliation(s)
- Felix Ulrich-Pur
- Austrian Academy of Sciences, Institute of High Energy Physics (HEPHY), Nikolsdorfer Gasse 18, A-1050 Wien, Austria
| | - Thomas Bergauer
- Austrian Academy of Sciences, Institute of High Energy Physics (HEPHY), Nikolsdorfer Gasse 18, A-1050 Wien, Austria
| | | | - Albert Hirtl
- TU Wien, Atominstitut, Stadionallee 2, A-1020 Wien, Austria
| | - Christian Irmler
- Austrian Academy of Sciences, Institute of High Energy Physics (HEPHY), Nikolsdorfer Gasse 18, A-1050 Wien, Austria
| | - Stefanie Kaser
- Austrian Academy of Sciences, Institute of High Energy Physics (HEPHY), Nikolsdorfer Gasse 18, A-1050 Wien, Austria
| | - Florian Pitters
- Austrian Academy of Sciences, Institute of High Energy Physics (HEPHY), Nikolsdorfer Gasse 18, A-1050 Wien, Austria
| | - Simon Rit
- Lyon University, INSA-Lyon, University Lyon1, UJM-Saint Etienne, CNRS, Inserm, CREATIS UMR5220, U1206, France
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Götz S, Dickmann J, Rit S, Krah N, Khellaf F, Schulte RW, Parodi K, Dedes G, Landry G. Evaluation of the impact of a scanner prototype on proton CT and helium CT image quality and dose efficiency with Monte Carlo simulation. Phys Med Biol 2022; 67. [PMID: 35086073 DOI: 10.1088/1361-6560/ac4fa4] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 01/27/2022] [Indexed: 11/12/2022]
Abstract
Objective.The use of ion computed tomography (CT) promises to yield improved relative stopping power (RSP) estimation as input to particle therapy treatment planning. Recently, proton CT (pCT) has been shown to yield RSP accuracy on par with state-of-the-art x-ray dual energy CT. There are however concerns that the lower spatial resolution of pCT compared to x-ray CT may limit its potential, which has spurred interest in the use of helium ion CT (HeCT). The goal of this study was to investigate image quality of pCT and HeCT in terms of noise, spatial resolution, RSP accuracy and imaging dose using a detailed Monte Carlo (MC) model of an existing ion CT prototype.Approach.Three phantoms were used in simulated pCT and HeCT scans allowing estimation of noise, spatial resolution and the scoring of dose. An additional phantom was used to evaluate RSP accuracy. The imaging dose required to achieve the same image noise in a water and a head phantom was estimated at both native spatial resolution, and in a scenario where the HeCT spatial resolution was reduced and matched to that of pCT using Hann windowing of the reconstruction filter. A variance reconstruction formalism was adapted to account for Hann windowing.Main results.We confirmed that the scanner prototype would produce higher spatial resolution for HeCT than pCT by a factor 1.8 (0.86 lp mm-1versus 0.48 lp mm-1at the center of a 20 cm water phantom). At native resolution, HeCT required a factor 2.9 more dose than pCT to achieve the same noise, while at matched resolution, HeCT required only 38% of the pCT dose. Finally, RSP mean absolute percent error (MAPE) was found to be 0.59% for pCT and 0.67% for HeCT.Significance.This work compared the imaging performance of pCT and HeCT when using an existing scanner prototype, with the spatial resolution advantage of HeCT coming at the cost of increased dose. When matching spatial resolution via Hann windowing, HeCT had a substantial dose advantage. Both modalities provided state-of-the-art RSP MAPE. HeCT might therefore help reduce the dose exposure of patients with comparable image noise to pCT, enhanced spatial resolution and acceptable RSP accuracy at the same time.
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Affiliation(s)
- S Götz
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), D-85748 Garching bei München, Germany
| | - J Dickmann
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), D-85748 Garching bei München, Germany
| | - S Rit
- University of Lyon, INSA-Lyon, Unversité Claude Bernard Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS, UMR 5220, U1294 F-69373, Lyon, France
| | - N Krah
- University of Lyon, INSA-Lyon, Unversité Claude Bernard Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS, UMR 5220, U1294 F-69373, Lyon, France.,IP2I, UMR 5822 F-69622, Villeurbanne, France
| | - F Khellaf
- University of Lyon, INSA-Lyon, Unversité Claude Bernard Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS, UMR 5220, U1294 F-69373, Lyon, France
| | - R W Schulte
- Division of Biomedical Engineering Sciences, Loma Linda University, Loma Linda, CA 92354, United States of America
| | - K Parodi
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), D-85748 Garching bei München, Germany
| | - G Dedes
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), D-85748 Garching bei München, Germany
| | - G Landry
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), D-85748 Garching bei München, Germany.,Department of Radiation Oncology, University Hospital, LMU Munich, D-81377 Munich, Germany.,German Cancer Consortium (DKTK), D-81377 Munich, Germany
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Dickmann J, Sarosiek C, Götz S, Pankuch M, Coutrakon G, Johnson RP, Schulte RW, Parodi K, Landry G, Dedes G. An empirical artifact correction for proton computed tomography. Phys Med 2021; 86:57-65. [PMID: 34058718 DOI: 10.1016/j.ejmp.2021.05.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 04/20/2021] [Accepted: 05/12/2021] [Indexed: 12/31/2022] Open
Abstract
PURPOSE To reduce image artifacts of proton computed tomography (pCT) from a preclinical scanner, for imaging of the relative stopping power (RSP) needed for particle therapy treatment planning using a simple empirical artifact correction method. METHODS We adapted and employed a correction method previously used for beam-hardening correction in x-ray CT which makes use of a single scan of a custom-built homogeneous phantom with known RSP. Exploiting the linearity of the filtered backprojection operation, a function was found which corrects water-equivalent path lengths (RSP line integrals) in experimental scans using a prototype pCT scanner. The correction function was applied to projection values of subsequent scans of a homogeneous water phantom, a sensitometric phantom with various inserts and an anthropomorphic head phantom. Data were acquired at two different incident proton energies to test the robustness of the method. RESULTS Inaccuracies in the detection process caused an offset and known ring artifacts in the water phantom which were considerably reduced using the proposed method. The mean absolute percentage error (MAPE) of mean RSP values of all inserts of the sensitometric phantom and the water phantom was reduced from 0.87% to 0.44% and from 0.86% to 0.48% for the two incident energies respectively. In the head phantom a clear reduction of artifacts was observed. CONCLUSIONS Image artifacts of experimental pCT scans with a prototype scanner could substantially be reduced both in homogeneous, heterogeneous and anthropomorphic phantoms. RSP accuracy was also improved.
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Affiliation(s)
- Jannis Dickmann
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), Am Coulombwall 1, Garching bei München, Germany.
| | - Christina Sarosiek
- Department of Physics, Northern Illinois University, 1425 W. Lincoln Highway, DeKalb, Illinois, United States.
| | - Stefanie Götz
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), Am Coulombwall 1, Garching bei München, Germany.
| | - Mark Pankuch
- Northwestern Medicine Chicago Proton Center, 4455 Weaver Parkway, Warrenville, Illinois, United States.
| | - George Coutrakon
- Department of Physics, Northern Illinois University, 1425 W. Lincoln Highway, DeKalb, Illinois, United States.
| | - Robert P Johnson
- Department of Physics, U.C. Santa Cruz, 1156 High Street, Santa Cruz, California, United States.
| | - Reinhard W Schulte
- Division of Biomedical Engineering Sciences, Loma Linda University, 11175 Campus Street, Loma Linda, California, United States.
| | - Katia Parodi
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), Am Coulombwall 1, Garching bei München, Germany.
| | - Guillaume Landry
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), Am Coulombwall 1, Garching bei München, Germany; Department of Radiation Oncology, University Hospital, LMU Munich, Marchioninistraße 15, Munich, Germany; German Cancer Consortium (DKTK), Marchioninistraße 15, Munich, Germany.
| | - George Dedes
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), Am Coulombwall 1, Garching bei München, Germany.
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Dickmann J, Kamp F, Hillbrand M, Corradini S, Belka C, Schulte RW, Parodi K, Dedes G, Landry G. Fluence-modulated proton CT optimized with patient-specific dose and variance objectives for proton dose calculation. Phys Med Biol 2021; 66:064001. [PMID: 33545701 DOI: 10.1088/1361-6560/abe3d2] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Particle therapy treatment planning requires accurate volumetric maps of the relative stopping power, which can directly be acquired using proton computed tomography (pCT). With fluence-modulated pCT (FMpCT) imaging fluence is concentrated in a region-of-interest (ROI), which can be the vicinity of the treatment beam path, and imaging dose is reduced elsewhere. In this work we present a novel optimization algorithm for FMpCT which, for the first time, calculates modulated imaging fluences for joint imaging dose and image variance objectives. Thereby, image quality is maintained in the ROI to ensure accurate calculations of the treatment dose, and imaging dose is minimized outside the ROI with stronger minimization penalties given to imaging organs-at-risk. The optimization requires an initial scan at uniform fluence or a previous x-ray CT scan. We simulated and optimized FMpCT images for three pediatric patients with tumors in the head region. We verified that the target image variance inside the ROI was achieved and demonstrated imaging dose reductions outside of the ROI of 74% on average, reducing the imaging dose from 1.2 to 0.3 mGy. Such dose savings are expected to be relevant compared to the therapeutic dose outside of the treatment field. Treatment doses were re-calculated on the FMpCT images and compared to treatment doses re-recalculated on uniform fluence pCT scans using a 1% criterion. Passing rates were above 98.3% for all patients. Passing rates comparing FMpCT treatment doses to the ground truth treatment dose were above 88.5% for all patients. Evaluation of the proton range with a 1 mm criterion resulted in passing rates above 97.5% (FMpCT/pCT) and 95.3% (FMpCT/ground truth). Jointly optimized fluence-modulated pCT images can be used for proton dose calculation maintaining the full dosimetric accuracy of pCT but reducing the required imaging dose considerably by three quarters. This may allow for daily imaging during particle therapy ensuring a safe and accurate delivery of the therapeutic dose and avoiding excess dose from imaging.
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Affiliation(s)
- J Dickmann
- Department of Medical Physics, Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU Munich), D-85748 Garching bei München, Germany
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Dickmann J, Sarosiek C, Rykalin V, Pankuch M, Coutrakon G, Johnson RP, Bashkirov V, Schulte RW, Parodi K, Landry G, Dedes G. Proof of concept image artifact reduction by energy-modulated proton computed tomography (EMpCT). Phys Med 2021; 81:237-244. [DOI: 10.1016/j.ejmp.2020.12.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 12/09/2020] [Accepted: 12/15/2020] [Indexed: 11/29/2022] Open
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Dickmann J, Sarosiek C, Rykalin V, Pankuch M, Rit S, Detrich N, Coutrakon G, Johnson RP, Schulte RW, Parodi K, Landry G, Dedes G. Experimental realization of dynamic fluence field optimization for proton computed tomography. ACTA ACUST UNITED AC 2020; 65:195001. [DOI: 10.1088/1361-6560/ab9f5f] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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Dedes G, Dickmann J, Giacometti V, Rit S, Krah N, Meyer S, Bashkirov V, Schulte R, Johnson RP, Parodi K, Landry G. The role of Monte Carlo simulation in understanding the performance of proton computed tomography. Z Med Phys 2020; 32:23-38. [PMID: 32798033 PMCID: PMC9948882 DOI: 10.1016/j.zemedi.2020.06.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2020] [Revised: 05/18/2020] [Accepted: 06/16/2020] [Indexed: 01/28/2023]
Abstract
Proton computed tomography (pCT) is a promising tomographic imaging modality allowing direct reconstruction of proton relative stopping power (RSP) required for proton therapy dose calculation. In this review article, we aim at highlighting the role of Monte Carlo (MC) simulation in pCT studies. After describing the requirements for performing proton computed tomography and the various pCT scanners actively used in recent research projects, we present an overview of available MC simulation platforms. The use of MC simulations in the scope of investigations of image reconstruction, and for the evaluation of optimal RSP accuracy, precision and spatial resolution omitting detector effects is then described. In the final sections of the review article, we present specific applications of realistic MC simulations of an existing pCT scanner prototype, which we describe in detail.
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Affiliation(s)
- George Dedes
- Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München (LMU Munich), Garching b. München, Germany.
| | - Jannis Dickmann
- Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München (LMU Munich), Garching b. München, Germany
| | - Valentina Giacometti
- The Patrick G Johnston Centre for Cancer Research, Queen's University of Belfast, Northern Ireland Cancer Centre, Belfast, Northern Ireland, United Kingdom
| | - Simon Rit
- University of Lyon, CREATIS, CNRS UMR5220; Inserm U1044, INSA-Lyon, Université Lyon 1, Centre Léon Bérard, Lyon, France
| | - Nils Krah
- University of Lyon, CREATIS, CNRS UMR5220; Inserm U1044, INSA-Lyon, Université Lyon 1, Centre Léon Bérard, Lyon, France,University of Lyon, Institute of Nuclear Physics Lyon (IPNL), CNRS UMR 5822, Villeurbanne, France
| | - Sebastian Meyer
- Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München (LMU Munich), Garching b. München, Germany,Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America
| | - Vladimir Bashkirov
- Division of Biomedical Engineering Sciences, Loma Linda University, Loma Linda, CA, United States of America
| | - Reinhard Schulte
- Division of Biomedical Engineering Sciences, Loma Linda University, Loma Linda, CA, United States of America
| | - Robert P. Johnson
- Department of Physics, U. C. Santa Cruz, Santa Cruz, CA, United States of America
| | - Katia Parodi
- Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München (LMU Munich), Garching b. München, Germany
| | - Guillaume Landry
- Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München (LMU Munich), Garching b. München, Germany,Department of Radiation Oncology, Department of Medical Physics, University Hospital, LMU Munich, Munich, Germany,German Cancer Consortium, (DKTK), Munich, Germany
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