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Ellin J, Rebolo L, Backfish M, Prebys E, Ariño-Estrada G. Prompt gamma timing for proton range verification with TlBr and TlCl as pure Cherenkov emitters. Phys Med Biol 2024; 69:115002. [PMID: 38657638 PMCID: PMC11106777 DOI: 10.1088/1361-6560/ad4304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 04/18/2024] [Accepted: 04/24/2024] [Indexed: 04/26/2024]
Abstract
Objective. Prompt gamma timing (PGT) uses the detection time of prompt gammas emitted along the range of protons in proton radiotherapy to verify the position of the Bragg peak (BP). Cherenkov detectors offer the possibility of enhanced signal-to-noise ratio (SNR) due to the inherent physics of Cherenkov emission which enhances detection of high energy prompt gamma rays relative to other induced uncorrelated signals. In this work, the PGT technique was applied to 3 semiconductor material slabs that emit only Cherenkov light for use in a full scale system: a 3 × 3 × 20 mm3TlBr, a 12 × 12 × 12 mm3TlBr, and a 5 × 5 × 5 mm3TlCl.Approach. A polymethyl methacrylate (PMMA) target was exposed to a 67.5 MeV, 0.5 nA proton beam and shifted in 3 mm increments at the Crocker nuclear laboratory (CNL) in Davis, CA, USA. A fast plastic scintillator coupled to a photomultiplier tube (PMT) provided the start reference for the proton time of flight. Time of flight (TOF) distributions were generated using this reference and the gamma-ray timestamp in the Cherenkov detector.Main results. The SNR of the proton correlated peaks relative to the background was 20, 29, and 30 for each of the three samples, respectively. The upper limit of the position resolutions with the TlCl sample were 2 mm, 3 mm, and 5 mm for 30k, 10k, and 5k detected events, respectively. The time distribution of events with respect to the reference reproduced with clarity the periodicity of the beam, implying a very high SNR of the Cherenkov crystals to detect prompt gammas. Background presence from the neutron-induced continuum, prompt gammas from deuterium, or positron activation were not observed. Material choice and crystal dimensions did not seem to affect significantly the outcome of the results.Significance. These results show the high SNR of the pure Cherenkov emitters TlBr and TlCl for the detection of prompt gammas in a proton beam with current of clinical significance and their potential for verifying the proton range. The accuracy in determining shifts of the BP was highly dependent on the number of events acquired, therefore, the performance of these detectors are expected to vary with different beam conditions such as current, pulse repetition, and proton bunch width.
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Affiliation(s)
- Justin Ellin
- Department of Biomedical Engineering, University of California Davis, CA, United States of America
| | - Leonor Rebolo
- Department of Biomedical Engineering, University of California Davis, CA, United States of America
| | - Michael Backfish
- Crocker Nuclear Laboratory, University of California Davis, CA, United States of America
| | - Eric Prebys
- Crocker Nuclear Laboratory, University of California Davis, CA, United States of America
- Department of Physics, University of California Davis, CA, United States of America
| | - Gerard Ariño-Estrada
- Department of Biomedical Engineering, University of California Davis, CA, United States of America
- Institut de Física d’Altes Energies—Barcelona Institute of Science and Technology, Bellaterra, Barcelona, Spain
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Rebolo L, Trigila C, Ellin J, Correia PMM, Silva AL, Veloso J, St James S, Roncali E, Ariño-Estrada G. Cherenkov Light Emission in Pure Cherenkov Emitters for Prompt Gamma Imaging. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2024; 8:15-20. [PMID: 38173701 PMCID: PMC10764010 DOI: 10.1109/trpms.2023.3323838] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Proton range verification (PRV) in proton therapy by means of prompt-gamma detection is a promising but challenging approach. High count rates, energies ranging between 1 MeV and 7 MeV, and a strong background complicate the detection of such particles. In this work, the Cherenkov light generated by prompt-gammas in the pure Cherenkov emitters TlBr, TlCl and PbF2 was studied. Cherenkov light in these crystals can provide a very fast timing signal with the potential to achieve very high count rates and to discern between prompt-gammas and background signals. Crystals of 1×1 cm2 and thicknesses of 1 cm, 2 cm, 3 cm and 4 cm were simulated. Different photodetector configurations were studied for 2.3 MeV, 4.4 MeV, and 6.1 MeV prompt-gammas. TlCl achieved the greatest number of detected Cherenkov photons for all energies, detector dimensions, and photodetector efficiency modeling. For the highest prompt-gamma energy simulated, TlCl yielded approximately 250 Cherenkov detected photons, using a hypothetical high-performance photodetector. Results show the crystal blocks of 1 cm × 1 cm × 1 cm have greater prompt-gamma detection efficiency per volume and a comparable average number of detected Cherenkov photons per event.
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Affiliation(s)
- L Rebolo
- Department of Biomedical Engineering at the University of California, Davis, Davis, California, USA
| | - C Trigila
- Department of Biomedical Engineering at the University of California, Davis, Davis, California, USA
| | - J Ellin
- Department of Biomedical Engineering at the University of California, Davis, Davis, California, USA
| | | | - A L Silva
- I3N-Physics Department of the University of Aveiro, Aveiro, Portugal
| | - J Veloso
- I3N-Physics Department of the University of Aveiro, Aveiro, Portugal
| | - S St James
- Huntsman Cancer Center in the University of Utah, Salt Lake City, Utah, USA
| | - E Roncali
- Department of Biomedical Engineering at the University of California, Davis, Davis, California, USA
- Department of Radiology at UC Davis
| | - G Ariño-Estrada
- Department of Biomedical Engineering at the University of California, Davis, Davis, California, USA
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He X, Trigila C, Ariño-Estrada G, Roncali E. Potential of Depth-of-Interaction-Based Detection Time Correction in Cherenkov Emitter Crystals for TOF-PET. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2023; 7:233-240. [PMID: 36994147 PMCID: PMC10042439 DOI: 10.1109/trpms.2022.3226950] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Cherenkov light can improve the timing resolution of Positron Emission Tomography (PET) radiation detectors, thanks to its prompt emission. Coincidence time resolutions (CTR) of ~30 ps were recently reported when using 3.2 mm-thick Cherenkov emitters. However, sufficient detection efficiency requires thicker crystals, causing the timing resolution to be degraded by the optical propagation inside the crystal. We report on depth-of-interaction (DOI) correction to mitigate the time-jitter due to the photon time spread in Cherenkov-based radiation detectors. We simulated the Cherenkov and scintillation light generation and propagation in 3 × 3 mm2 lead fluoride, lutetium oxyorthosilicate, bismuth germanate, thallium chloride, and thallium bromide. Crystal thicknesses varied from 9 to 18 mm with a 3-mm step. A DOI-based time correction showed a 2-to-2.5-fold reduction of the photon time spread across all materials and thicknesses. Results showed that highly refractive crystals, though producing more Cherenkov photons, were limited by an experimentally obtained high-cutoff wavelength and refractive index, restricting the propagation and extraction of Cherenkov photons mainly emitted at shorter wavelengths. Correcting the detection time using DOI information shows a high potential to mitigate the photon time spread. These simulations highlight the complexity of Cherenkov-based detectors and the competing factors in improving timing resolution.
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Affiliation(s)
- Xuzhi He
- Department of Biomedical Engineering at the University of California Davis, Davis, CA 95616 USA
| | - Carlotta Trigila
- Department of Biomedical Engineering at the University of California Davis, Davis, CA 95616 USA
| | - Gerard Ariño-Estrada
- Department of Biomedical Engineering at the University of California Davis, Davis, CA 95616 USA
| | - Emilie Roncali
- Department of Biomedical Engineering at the University of California Davis, Davis, CA 95616 USA
- Department of Radiology at University of California Davis, Sacramento, CA 95817 USA
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Trigila C, Ariño-Estrada G, Kwon SI, Roncali E. The Accuracy of Cerenkov Photons Simulation in Geant4/Gate Depends on the Parameterization of Primary Electron Propagation. FRONTIERS IN PHYSICS 2022; 10:891602. [PMID: 37220601 PMCID: PMC10201934 DOI: 10.3389/fphy.2022.891602] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Energetic electrons traveling in a dispersive medium can produce Cerenkov radiation. Cerenkov photons' prompt emission, combined with their predominantly forward emission direction with respect to the parent electron, makes them extremely promising to improve radiation detector timing resolution. Triggering gamma detections based on Cerenkov photons to achieve superior timing resolution is challenging due to the low number of photons produced per interaction. Monte Carlo simulations are fundamental to understanding their behavior and optimizing their pathway to detection. Therefore, accurately modeling the electron propagation and Cerenkov photons emission is crucial for reliable simulation results. In this work, we investigated the physics characteristics of the primary electrons (velocity, energy) and those of all emitted Cerenkov photons (spatial and timing distributions) generated by 511 keV photoelectric interactions in a bismuth germanate crystal using simulations with Geant4/GATE. Geant4 uses a stepwise particle tracking approach, and users can limit the electron velocity change per step. Without limiting it (default Geant4 settings), an electron mean step length of ~250 μm was obtained, providing only macroscopic modeling of electron transport, with all Cerenkov photons emitted in the forward direction with respect to the incident gamma direction. Limiting the electron velocity change per step reduced the electron mean step length (~0.200 μm), leading to a microscopic approach to its transport which more accurately modeled the electron physical properties in BGO at 511 keV. The electron and Cerenkov photons rapidly lost directionality, affecting Cerenkov photons' transport and, ultimately, their detection. Results suggested that a deep understanding of low energy physics is crucial to perform accurate optical Monte Carlo simulations and ultimately use them in TOF PET detectors.
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Affiliation(s)
- Carlotta Trigila
- Department of Biomedical Engineering, University of California Davis, Davis, CA, United States
| | - Gerard Ariño-Estrada
- Department of Biomedical Engineering, University of California Davis, Davis, CA, United States
| | - Sun Il Kwon
- Department of Biomedical Engineering, University of California Davis, Davis, CA, United States
| | - Emilie Roncali
- Department of Biomedical Engineering, University of California Davis, Davis, CA, United States
- Department of Radiology, University of California Davis, Davis, CA, United States
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Kratochwil N, Gundacker S, Auffray E. A roadmap for sole Cherenkov radiators with SiPMs in TOF-PET. Phys Med Biol 2021; 66. [PMID: 34433139 DOI: 10.1088/1361-6560/ac212a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 08/25/2021] [Indexed: 11/11/2022]
Abstract
Time of flight positron emission tomography can strongly benefit from a very accurate time estimator given by Cherenkov radiation, which is produced upon a 511 keV positron-electron annihilation gamma interaction in heavy inorganic scintillators. While time resolution in the order of 30 ps full width at half maximum (FWHM) has been reported using MCP-PMTs and black painted Cherenkov radiators, such solutions have several disadvantages, like high cost and low detection efficiency of nowadays available MCP-PMTs. On the other hand, silicon photomultipliers (SiPMs) are not limited by those obstacles and provide high photon detection efficiency with a decent time response. Timing performance of PbF2crystals of various lengths and surface conditions coupled to SiPMs was evaluated against a reference detector with an optimized test setup using high-frequency readout and novel time walk correction, with special attention on the intrinsic limits for one detected Cherenkov photon only. The average number of detected Cherenkov photons largely depends on the crystal surface state, resulting in a tradeoff between low photon time spread, thus good timing performance, and sensitivity. An intrinsic Cherenkov photon yield of 16.5 ± 3.3 was calculated for 2 × 2 × 3 mm3sized PbF2crystals upon 511 keVγ-deposition. After time walk correction based on the slew rate of the signal, assuming two identical detector arms in coincidence, and using all events, a time resolution of 215 ps FWHM (142 ps FWHM) was obtained for 2 × 2 × 20 mm3(2 × 2 × 3 mm3) sized PbF2crystals, compared to 261 ps (190 ps) without correction. Selecting on one detected photon only, a single photon coincidence time resolution of 113 ps FWHM for black painted and 166 ps for Teflon wrapped crystals was measured for 3 mm length, compared to 145 ps (black) and 263 ps (Teflon) for 20 mm length.
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Affiliation(s)
- Nicolaus Kratochwil
- CERN, Esplanade des Particules 1, 1211 Meyrin, Switzerland.,University of Vienna, Universitaetsring 1, A-1010 Vienna, Austria
| | - Stefan Gundacker
- CERN, Esplanade des Particules 1, 1211 Meyrin, Switzerland.,Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstrasse 55, D-52074 Aachen, Germany
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