Cherenkov Light Imaging Research Articles

Dose distribution measurements using luminol water during irradiation of high-energy X-rays from medical linear accelerators (LINAC)

Dose distribution measurements of high-energy X-rays from a medical linear accelerator (LINAC) in water are important for quality control (QC) of the system, and Cherenkov-light imaging is an efficient method for measuring the high-energy X-ray dose distribution. However, the depth profiles have an underestimated dose at increased depths due to the angular dependency of the Cherenkov light. Luminol water is a possible material for measuring the dose distribution by detecting the light emitted from the chemical reaction with the reactive hydroxyl radical (・OH) produced in water by irradiation. In this study, we used luminol water for dose distribution measurements of high-energy X-rays from a LINAC. Imaging of the light emitted from luminol water was conducted using a cooled charge-coupled device (CCD) camera during irradiation with 6 MV X-rays from a LINAC to the luminol water. Imaging of the Cherenkov light in water was also conducted by irradiating 6 MV X-rays to water for correcting the Cerenkov-light component produced in luminol water. The Cherenkov-light image was subtracted from that of the luminol water to derive a dose image. The light emission of luminol water was ∼3 times higher than that of Cherenkov light in water. By subtracting the Cherenkov-light image from the luminol-water image, we could obtain an image that was identical to the dose distributions. The difference in the relative dose distribution was within −0.4% for the corrected image while that of the Cherenkov-light image was −7.9%. The multiple irradiations of luminol water with X-rays produced non-uniformity of emitted light, probably due to the production of hydrogen peroxide (H2O2) in water. We confirmed that imaging luminol water was promising for dose distribution imaging by correcting the Cherenkov-light component in the images. The non-uniformity of the emitted light by multiple irradiations in luminol water needs to be solved for more stable measurements.

Cherenkov-light imaging of induced positron distribution in liquid water after proton beam irradiation

Imaging of positrons induced by nuclear reactions with a proton beam is a possible method for observing the beam shape from outside the subject. However, such imaging of induced positrons has so far been conducted for solid materials. The induced positron distribution in liquid water has not been measured or reported. To clarify the distribution of induced positrons in liquid water, we conducted Cherenkov-light imaging after irradiation by protons to a water phantom. After irradiation by a 117-MeV proton beam to a phantom containing liquid water, Cherenkov-light imaging of the induced positrons was conducted using a cooled charge-coupled device (CCD) camera following the decay of the positrons. We also imaged the luminescence of water during irradiation by the proton beam to compare the distributions. We could measure the distribution of Cherenkov-light from the induced positrons in liquid water. Positron distributions kept their beam shapes in water but were different from that of the luminescence image; positron distribution was wider in the deep area of the beams in the lateral as well as depth direction. The distributions' shapes were only slightly changed with time. We conclude that Cherenkov-light imaging from the induced positrons after irradiation by a proton beam in water was possible, and we found that the induced positrons kept their beam shape in water with different shape from that of dose. These findings may provide new insights for imaging in particle therapy.

Differences of the intensity increase of optical signals with fluorescein between Cherenkov-light and luminescence of water

The imaging of the luminescence of water and Cherenkov-light with fluorescein during irradiation is a useful method to increase intensity; however, the magnitudes of the increase in intensity for Cherenkov-light and luminescence of water have been neither evaluated nor compared. Therefore, we measured the Cherenkov-light and luminescence of water with and without fluorescein during irradiation, and then we compared the magnitudes of the intensity increase with fluorescein. For 6 and 10 MV X-rays as well as 6 and 12 MeV electrons, the intensity of the Cherenkov-light images increased only 2 to 3 times with fluorescein water compared with that of water. Meanwhile, for 100 kV X-rays and 150 MeV protons, the intensity of the luminescence images increased more than 10 times with fluorescein water compared with that of water. The difference could probably be attributed to the difference in the light-emission mechanisms and coherency between Cherenkov-light and the luminescence of water.

Technical note: Correcting angular dependencies using non-polarized components of Cherenkov light in water during high-energy X-ray irradiation.

Dose distribution measurements of high-energy X-rays from medical linear accelerators (LINAC) in water are important for quality control (QC) of the system. Although Cherenkov-light imaging is a useful method for measuring the high-energy X-ray dose distribution, depth profiles have an underestimated dose at increased depths due to the angular dependency of the Cherenkov light generated in water. In this study, we use a linear polarizer to separate the majority of polarized components from the majority of unpolarized components of Cherenkov-light images in water and then use this information to correct for angular dependencies. A water phantom, a cooled charge-coupled device (CCD) camera, and a polarizer were installed in a black box. Then, the water phantom was irradiated from the upper side with 6 or 10 MV X-rays, and the Cherenkov light generated in water was imaged with the polarizer axis at both parallel and perpendicular orientations to the beam. By using these images from the two orientations relative to the beam, we corrected the angular dependency of the Cherenkov light. By subtracting the images measured with the polarizer perpendicular to the beams from the images measured with the polarizer parallel to the beams, we could obtain images with only the polarized components. Using these images, we could calculate the images with non-polarized components that had similar depth profiles to those calculated with a planning system. The average difference between corrected depth profiles and those calculated with the planning system was less than 1%, while that between uncorrected depth profiles and the planning system was more than 8.3% in depths of water from 20 to 100mm. We conclude that the use of the polarizer has the potential to improve the accuracy of dose distribution in Cherenkov-light imaging of water using high-energy X-rays.

Optical imaging of decayed positrons and muons with different collimators

Although optical imaging of decayed positrons and muons can provide promising methods, it has been attempted only for muons without a collimator, and the beam characteristics with collimators, such as peak position or beam spread in depth and lateral directions, have not yet been evaluated. Therefore, we conducted optical imaging of decayed positrons and muons with different collimators. For the imaging of decayed positrons, Cherenkov-light imaging in fluorescein (FS) water was used, while imaging of a plastic scintillator block was used for the imaging of muons. We conducted these imaging trials during irradiation with 84.5-MeV/c positive muons to an FS water phantom or a plastic scintillator block using a cooled charge-coupled device (CCD) camera with each collimator of a different diameter attached to the beam port. We could measure the Cherenkov-light images of FS water of decayed positrons and optical images of muons using the plastic scintillator block for all collimators. The depth profiles of the Cherenkov-light images were slightly wider for the muons with the collimators of larger diameters, although the estimated peak depths were nearly the same for all collimators. The lateral profiles of the Cherenkov light were wider for the muons when using collimators of larger diameters. Asymmetry in the directions of positron emissions from the muons was observed for all collimators. The depth profiles of the optical image of muons using a plastic scintillator block had nearly the same shape. The estimated lateral widths of the optical images of the plastic scintillator block were the same sizes as the collimator diameters within a 1.1-mm difference at a 10-mm depth of the scintillator block, and the widths were wider at the Bragg peak. With these measured optical images, we conclude that Cherenkov-light imaging of decayed positrons in water and optical imaging of muons using a plastic scintillator block with collimators are useful methods for determining not only peak position but also beam width as well as the asymmetry of the directions of positron emissions from the muons.

Position-sensitive vacuum photon detectors

This article reviews the principles, performance and limitations of position-sensitive vacuum photon detectors which find applications in high-energy physics experiments. Particular emphasis is devoted to multi-anode photo-multiplier tubes, devices based on micro-channel plates and hybrid photon detectors. Over the past 25 years, innovation in industrial environments, research centres and universities has led to the invention and consequent optimization of a number of position-sensitive photon detectors. Miniaturization of known principles and components or the smart combination of established concepts allowed to build new classes of finely-segmented photodetectors which in turn enabled new applications in high-energy physics, but also elsewhere. The imaging of Cherenkov light in hostile hadron environments like at the CERN Large Hadron Collider is perhaps one of the most demanding applications which would not have been possible without this breakthrough.

Cherenkov light imaging in particle and nuclear physics experiments

Abstract Ring Imaging Cherenkov Detectors (RICH) play a significant role in particle and nuclear physics experiments providing particle identification. They work exceptionally well for hadron identification as there are few other techniques that can differentiate between pions kaons and protons in the multi-GeV/c momentum range. This article is a review of detectors using Cherenkov light imaging viewed from a historical perspective and following the evolution of the techniques and technologies.

Cherenkov light imaging in astroparticle physics

Cherenkov light induced by fast charged particles in transparent dielectric media such as air or water is exploited by a variety of experimental techniques to detect and measure extraterrestrial particles impinging on Earth. A selection of detection principles is discussed and corresponding experiments are presented together with breakthrough-results they achieved. Some future developments are highlighted.

An investigation of clinical treatment field delivery verification using cherenkov imaging: IMRT positioning shifts and field matching.

Cherenkov light emission has been shown to correlate with ionizing radiation dose delivery in solid tissue. An important clinical application of Cherenkov light is the real-time verification of radiation treatment delivery invivo. To test the feasibility of treatment field verification, Cherenkov light images were acquired concurrent with radiation beam delivery to standard and anthropomorphic phantoms. Specifically, we tested two clinical treatment scenarios: (a) Observation of field overlaps or gaps in matched 3D fields and (b) Patient positioning shifts during intensity modulated radiation therapy (IMRT) field delivery. Further development of this technique would allow real-time detection of treatment delivery errors on the order of millimeters so that patient safety and treatment quality can be improved. Cherenkov light emission was captured using a PI-MAX4 intensified charge coupled device (ICCD) system (Princeton Instruments). All radiation delivery was performed using a Varian Trilogy linear accelerator (linac) operated at 6MV or 18MV for photon and 6MeV or 16MeV for electron studies. Field matching studies were conducted with photon and electron beams at gantry angles of 0°, 15°, and 45°. For each modality and gantry angle, a total of three data sets were acquired. Overlap and gap distances of 0, 2, 5, and 10mm were tested and delivered to solid phantom material of 30×30×5cm3 . Phantom materials used were white plastic water and brown solid water. Tests were additionally performed on an anthropomorphic phantom with an irregular surface. Positioning shift studies were performed using IMRT fields delivered to a thoracic anthropomorphic phantom. For thoracic phantom measurements, the camera was placed laterally to observe the entire right side of the phantom. Fields were delivered with known translational patient positioning shifts in four directions. Changes in the Cherenkov fluence were evaluated through the generation of difference maps from unshifted Cherenkov images. All images were evaluated using ImageJ, Python, and MATLAB software packages. For matched fields, Cherenkov images were able to quantitate matched field separations with discrepancies between 2 and 4mm, depending on gantry angle and beam energy or modality. For all photon and electron beams delivered at a gantry angle of 0°, image analysis indicated average discrepancies of less than 2mm for all field gaps and overlaps, with 83% of matched fields exhibiting discrepancies less than 1mm. Beams delivered obliquely to the phantom surface exhibited average discrepancies as high as 4mm for electron beams delivered at large oblique angles. Finally, for IMRT field delivery, vertical and lateral patient positioning shifts of 2mm were detected in some cases, indicating the potential detectability threshold of using this technique alone. Our study indicates that Cherenkov imaging can be used to support and bolster current treatment delivery verification techniques, improving our ability to recognize and rectify millimeter-scale delivery and positioning errors.

A compact and light-weight refractive telescope for the observation of extensive air showers

A general purpose instrument for imaging of Cherenkov light or fluorescence light emitted by extensive air showers is presented. Its refractive optics allows for a compact and light-weight design with a wide field-of-view of 12°. The optical system features a 0.5 m diameter Fresnel lens and a camera with 61 pixels composed of Winston cones and large-sized 6x6 mm2 photo sensors. As photo sensors, semi conductor light sensors (SiPMs) are utilized. The camera provides a high photon detection efficiency together with robust operation. The enclosed optics permit operation in regions of harsh environmental conditions. The low price of the telescope allows the production of a large number of telescopes and the application of the instrument in various projects, such as FAMOUS for the Pierre Auger Observatory, HAWC's Eye for HAWC or IceAct for IceCube. In this paper the novel design of this telescope and first measurements are presented.

Cherenkov light imaging in particle and nuclear physics experiments

This article describes Cherenkov light imaging techniques used in the particle and nuclear physics experiments, concentrating on the author’s personal overview of selected recent counters.

Development of a Cherenkov light imaging system for studying the dynamics of radiocesium in plants

ABSTRACTHigh-resolution images of radiocesium (137Cs) distribution are required to study cesium kinetics in plants. A Cherenkov light imaging system can visualize fine distributions of radionuclides emitting beta particles using an optical camera. To evaluate the linearity of the system, an imaging test was performed with point sources of 137Cs, with a radioactivity of 10–2000 kBq. The results indicated that the system has a good linearity between the image intensity and the radioactivity of 137Cs. We developed an imaging system for plants using this system to study radiocesium movement in intact plants. To demonstrate the ability to image radiocesium in a plant, an experiment was performed with an intact soybean plant for four days. The root of an 11-day-old soybean plant was dipped in 20 mL of a culture solution containing 137Cs with a radioactivity of 10 MBq without potassium. After one day, the solution was replaced with one with potassium but no 137Cs. The soybean plant was in healthy condition in the system, and the high-resolution serial images indicated that 137Cs was transported to the shoot and accumulated in the node. Therefore, Cherenkov light imaging is promising for imaging radiocesium in intact plants.

Cherenkov light imaging tests with state-of-the-art solid state photon counter for the CLAS12 RICH detector

A large area ring-imaging Cherenkov detector will be operated for hadron identification in the 3GeV/c to 8GeV/c momentum range at the CLAS12 experiment at the upgraded continuous electron beam accelerator facility of Jefferson Lab. The detector, consisting of aerogel radiator, composite mirrors and photon counters, will be built with a hybrid optics design to allow the detection of Cherenkov light for both forward and large angle hadron tracks. The active area has to be densely packed and highly segmented, covering about 1m2 with pixels of 6mm2, and to allow a time resolution of 1ns. A technology that can offer a cost-effective solution and low material budget could be Silicon Photomultipliers (SiPM) thanks to their high gain at low bias voltage, fast timing, good single-photoelectron resolution and insensitivity to magnetic fields. An investigation is ongoing on samples of 3×3mm2 SiPM of different micro-cell size to assess the single photon detection capability in the presence of high dark count rate due to thermal generation effects, after-pulses or optical cross-talk and to study the response to the moderate radiation damage expected at CLAS12. In this work, a brief review of the latest and most interesting results from these studies will be shown.

SU‐G‐IeP4‐06: Feasibility of External Beam Treatment Field Verification Using Cherenkov Imaging

Purpose:Cherenkov light emission has been shown to correlate with ionizing radiation (IR) dose delivery in solid tissue. In order to properly correlate Cherenkov light images with real time dose delivery in a patient, we must account for geometric and intensity distortions arising from observation angle, as well as the effect of monitor units (MU) and field size on Cherenkov light emission. To test the feasibility of treatment field verification, we first focused on Cherenkov light emission efficiency based on MU and known field size (FS).Methods:Cherenkov light emission was captured using a PI‐MAX4 intensified charge coupled device(ICCD) system (Princeton Instruments), positioned at a fixed angle of 40° relative to the beam central axis. A Varian TrueBeam linear accelerator (linac) was operated at 6MV and 600MU/min to deliver an Anterior‐Posterior beam to a 5cm thick block phantom positioned at 100cm Source‐to‐Surface‐Distance(SSD). FS of 10×10, 5×5, and 2×2cm2 were used. Before beam delivery projected light field images were acquired, ensuring that geometric distortions were consistent when measuring Cherenkov field discrepancies. Cherenkov image acquisition was triggered by linac target current. 500 frames were acquired for each FS. Composite images were created through summation of frames and background subtraction. MU per image was calculated based on linac pulse delay of 2.8ms. Cherenkov and projected light FS were evaluated using ImageJ software.Results:Mean Cherenkov FS discrepancies compared to light field were <0.5cm for 5.6, 2.8, and 8.6 MU for 10×10, 5×5, and 2×2cm2 FS, respectably. Discrepancies were reduced with increasing field size and MU. We predict a minimum of 100 frames is needed for reliable confirmation of delivered FS.Conclusion:Current discrepancies in Cherenkov field sizes are within a usable range to confirm treatment delivery in standard and respiratory gated clinical scenarios at MU levels appropriate to standard MLC position segments

Ultra-high resolution of radiocesium distribution detection based on Cherenkov light imaging

After the nuclear disaster in Fukushima, radiocesium contamination became a serious scientific concern and research of its effects on plants increased. In such plant studies, high resolution images of radiocesium are required without contacting the subjects. Cherenkov light imaging of beta radionuclides has inherently high resolution and is promising for plant research. Since 137Cs and 134Cs emit beta particles, Cherenkov light imaging will be useful for the imaging of radiocesium distribution. Consequently, we developed and tested a Cherenkov light imaging system. We used a high sensitivity cooled charge coupled device (CCD) camera (Hamamatsu Photonics, ORCA2-ER) for imaging Cherenkov light from 137Cs. A bright lens (Xenon, F-number: 0.95, lens diameter: 25mm) was mounted on the camera and placed in a black box. With a 100-μm 137Cs point source, we obtained 220-μm spatial resolution in the Cherenkov light image. With a 1-mm diameter, 320-kBq 137Cs point source, the source was distinguished within 2-s. We successfully obtained Cherenkov light images of a plant whose root was dipped in a 137Cs solution, radiocesium-containing samples as well as line and character phantom images with our imaging system. Cherenkov light imaging is promising for the high resolution imaging of radiocesium distribution without contacting the subject.

Cherenkov light imaging in astro-particle physics

Cherenkov light emission plays a key role in contemporary science; it is widely used in high energy, nuclear, and numerous astro-particle physics experiments. Most astro-particle physics experiments are based on the detection of light, and a vast majority of them on the measurement of Cherenkov light. Cherenkov light emission is measured in gases (used in air-Cherenkov technique), in water (for example, neutrino experiments BAIKAL, Super-Kamiokande, NESTOR, ANTARES, future KM3NeT; cosmic and γ-ray experiments Milagro, HAWC, AUGER) and in ice (IceCube). In this report our goal is not limited to simply listing the multitude of experiments that are based on using Cherenkov emission, but we will clarify the reasons making this emission so important and so frequently used. For completeness we will first give a short historical overview on the discovery and evolution of Cherenkov emission and then we will dwell on its main features and numerous applications in astro-particle physics experiments.

Cherenkov Video Imaging Allows for the First Visualization of Radiation Therapy in Real Time

To determine whether Cherenkov light imaging can visualize radiation therapy in real time during breast radiation therapy. An intensified charge-coupled device (CCD) camera was synchronized to the 3.25-μs radiation pulses of the clinical linear accelerator with the intensifier set × 100. Cherenkov images were acquired continuously (2.8 frames/s) during fractionated whole breast irradiation with each frame an accumulation of 100 radiation pulses (approximately 5 monitor units). The first patient images ever created are used to illustrate that Cherenkov emission can be visualized as a video during conditions typical for breast radiation therapy, even with complex treatment plans, mixed energies, and modulated treatment fields. Images were generated correlating to the superficial dose received by the patient and potentially the location of the resulting skin reactions. Major blood vessels are visible in the image, providing the potential to use these as biological landmarks for improved geometric accuracy. The potential for this system to detect radiation therapy misadministrations, which can result from hardware malfunction or patient positioning setup errors during individual fractions, is shown. Cherenkoscopy is a unique method for visualizing surface dose resulting in real-time quality control. We propose that this system could detect radiation therapy errors in everyday clinical practice at a time when these errors can be corrected to result in improved safety and quality of radiation therapy.

Discovery of extended VHEγ-ray emission from the vicinity of the young massive stellar cluster Westerlund 1

Results obtained in very-high-energy (VHE; E > 100 GeV) \gamma-ray observations performed with the H.E.S.S. telescope array are used to investigate particle acceleration processes in the vicinity of the young massive stellar cluster Westerlund 1 (Wd 1). Imaging of Cherenkov light from \gamma-ray induced particle cascades in the Earth's atmosphere is used to search for VHE \gamma\ rays from the region around Wd 1. Possible catalogued counterparts are searched for and discussed in terms of morphology and energetics of the H.E.S.S. source. The detection of the degree-scale extended VHE \gamma-ray source HESS J1646-458 is reported based on 45 hours of H.E.S.S. observations performed between 2004 and 2008. The VHE \gamma-ray source is centred on the nominal position of Wd 1 and detected with a total statistical significance of ~20\sigma. The emission region clearly extends beyond the H.E.S.S. point-spread function (PSF). The differential energy spectrum follows a power law in energy with an index of \Gamma=2.19 \pm 0.08_{stat} \pm 0.20_{sys} and a flux normalisation at 1 TeV of \Phi_0 = (9.0 \pm 1.4_{stat} \pm 1.8_{sys}) x 10^{-12} TeV^{-1} cm^{-2} s^{-1}. The integral flux above 0.2 TeV amounts to (5.2 \pm 0.9) x 10^{-11} cm^{-2} s^{-1}. Four objects coincident with HESS J1646-458 are discussed in the search of a counterpart, namely the magnetar CXOU J164710.2-455216, the X-ray binary 4U 1642-45, the pulsar PSR J1648-4611 and the massive stellar cluster Wd 1. In a single-source scenario, Wd 1 is favoured as site of VHE particle acceleration. Here, a hadronic parent population would be accelerated within the stellar cluster. Beside this, there is evidence for a multi-source origin, where a scenario involving PSR J1648-4611 could be viable to explain parts of the VHE \gamma-ray emission of HESS J1646-458.

Cherenkov light imaging—Fundamentals and recent developments

We review in a historical way the fundamentals of Cherenkov light imaging applied to ring imaging Cherenkov counters. We also point out some of the newer developments in this very active field.

Cherenkov detectors in the ALICE experiment at LHC

The ALICE experiment is devoted to measure the properties of the strongly interacting matter created in heavy-ion collisions at LHC at S N N = 5.5 TeV . The ALICE-HMPID is a ring imaging Cherenkov detector with liquid C6F14 as radiator, dedicated to the identification of charged pions and kaons in the range 1 ≤ p ≤ 3 GeV/c and protons in the range 2 ≤ p ≤ 5 GeV/c . It consists of seven identical proximity focusing RICH counters, exploiting large area MWPC equipped with CsI photocathodes, for Cherenkov light imaging. Furthermore, results from experiments at RHIC and theoretical studies have shown that to understand the hadronization mechanisms in heavy-ion collisions is very important to identify track-by-track charged hadrons at larger momenta ( 10 − 30 GeV/c ). Therefore an upgrade of ALICE PID capability is advisable. A possible upgrade is under study and it consists of a ring imaging Cherenkov detector, called VHMPID. HMPID characteristics and results from cosmic and first beam data taking are described. Description of VHMPID and performance results from simulation are also reported.