Plastic Scintillator Block Research Articles

A 3D imaging system for dosimetry in FLASH radiotherapy

This study examines the feasibility of reconstructing the spatial dose distribution delivered by a 9 MeV electron beam within a plastic scintillator block using optical tomography. The system is designed for use in 3D-dosimetry for clinical applications in quality assurance and beam characterization, especially with FLASH-beam sources. The proposed detector reconstructs the 3D dose distribution map employing a monolith with 10 cm side, imaged in four different projections by scientific cameras. The 3D dose distribution simulated with Geant4 was reconstructed using a maximum likelihood expectation maximization algorithm applied to the lateral projection, resulting in a longitudinal image with a standard deviation of 0.2 Gy. Furthermore, a preliminary experimental test has been performed.

High spatiotemporal resolution scintillation imaging of pulsed pencil beam scanning proton beams produced by a gantry-mounted synchrocyclotron.

A dosimeter with high spatial and temporal resolution would be of significant interest for pencil beam scanning (PBS) proton beams' characterization, especially when facing small fields and beams with high temporal dynamics. Optical imaging of scintillators has potential in providing sub-millimeter spatial resolution with pulse-by-pulse basis temporal resolution when the imaging system is capable of operating in synchrony with the beam-producing accelerator. We demonstrate the feasibility of imaging PBS proton beams as they pass through a plastic scintillator detector to simultaneously obtain multiple beam parameters, including proton range, pencil beam's widths at different depths, spot's size, and spot's position on a pulse-by-pulse basis with sub-millimeter resolution. A PBS synchrocyclotron was used for proton irradiation. A BC-408 plastic scintillator block with 30 × 30 × 5 cm3 size, and another block with 30 × 30 × 0.5 cm3 size, positioned in an optically sealed housing, were used sequentially to measure the proton range, and spot size/location, respectively. A high-speed complementary metal-oxide-semiconductor (CMOS) camera system synchronized with the accelerator's pulses through a gating module was used for imaging. Scintillation images, captured with the camera directly facing the 5-cm-thick scintillator, were corrected for background (BG), and ionization quenching of the scintillator to obtain the proton range. Spots' position and size were obtained from scintillation images of the 0.5-cm-thick scintillator when a 45° mirror was used to reflect the scintillation light toward the camera. Scintillation images with 0.16mm/pixel resolution corresponding to all proton pulses were captured. Pulse-by-pulse analysis showed that variations of the range, spots' position, and size were within±0.2% standard deviation of their average values. The absolute ranges were within±1mm of their expected values. The average spot-positions were mostly within±0.8mm and spots' sigma agreed within 0.2mm of the expected values. Scintillation-imaging PBS beams with high-spatiotemporal resolution is feasible and may help in efficient and cost-effective acceptance testing and commissioning of existing and even emerging technologies such as FLASH, grid, mini-beams, and so forth.

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.

Optical imaging of muons

Optical imaging of particle beams is a promising method for range and width estimations. However it was not clear that optical imaging was possible for muons. To clarify this, we conducted optical imaging of muons, since high-intensity muons are now available at J-PARC. We irradiated positive muons with different momenta to water or plastic scintillator block, and imaged using a charge-coupled device (CCD) camera during irradiation. The water and plastic scintillator block produced quite different images. The images of water during irradiation of muons produced elliptical shape light distribution at the end of the ranges due to Cherenkov-light from the positrons produced by positive muon decay, while, for the plastic scintillator block, we measured images similar to the dose distributions. We were able to estimate the ranges of muons as well as the measurement of the asymmetry of the direction of the positron emission by the muon decays from the optical images of the water, although the measured ranges were 4 mm to 5 mm larger than the calculated values. The ranges and widths of the beams could also be estimated from the optical images of the plastic scintillator block. We confirmed that optical imaging of muons was possible and is a promising method for the quality assessment, research of muons, and the future muon radiotherapy.

Optical imaging of produced light in water during irradiation of gamma photons lower energy than the Cerenkov-light threshold

It is commonly believed that gamma photon irradiation to water does not produce light in water if the gamma photon energy is lower than the Cerenkov-light threshold and imaging of gamma photon is impossible because the produced electrons from gamma photons do not emit light. However, we found that the light is produced in water and the imaging of produced light in water was possible with gamma photon irradiation even at lower energy than the Cerenkov-light threshold. We irradiated gamma photons with lower energy than the Cerenkov-light threshold (260 keV for electrons in water) from 99mTc (gamma photon energy of 140.5 keV) to water phantom, optical imaging was carried out with a charge-coupled device (CCD) camera. Also we conducted imaging of the gamma photons irradiation to acrylic and plastic scintillator blocks. The optical images of water were observed from 3600 s exposure time, and the intensity of the luminescence was linearly increased with time although the intensity was ~0.001% of that with the plastic scintillator block. The optical imaging of water during irradiation of gamma photons lower energy than the Cerenkov-light threshold was possible and it could be a new method for distribution measurements of gamma photons in water.

SU‐F‐J‐190: Time Resolved Range Measurement System Using Scintillator and CCD Camera for the Slow Beam Extraction

Purpose:To investigate the time structure of the range, we have verified the rang shift due to the betatron tune shift with several synchrotron parameters.Methods:A cylindrical plastic scintillator block and a CCD camera were installed on the black box. Using image processing, the range was determined the 80 percent of distal dose of the depth light distribution. The root mean square error of the range measurement using the scintillator and CCD system is about 0.2 mm. Range measurement was performed at interval of 170 msec. The chromaticity of the synchrotron was changed in the range of plus or minus 1% from reference chromaticity in this study. All of the particle inside the synchrotron ring were extracted with the output beam intensity 1.8×108 and 5.0×107 particle per sec.Results:The time strictures of the range were changed by changing of the chromaticity. The reproducibility of the measurement was sufficient to observe the time structures of the range. The range shift was depending on the number of the residual particle inside the synchrotron ring.Conclusion:In slow beam extraction for scanned carbon‐ion therapy, the range shift is undesirable because it causes the dose uncertainty in the target. We introduced the time‐resolved range measurement using scintillator and CCD system. The scintillator and CCD system have enabled to verify the range shift with sufficient spatial resolution and reproducibility.

Technical Note: Range verification system using edge detection method for a scintillator and a CCD camera system.

Three-dimensional irradiation with a scanned carbon-ion beam has been performed from 2011 at the authors' facility. The authors have developed the rotating-gantry equipped with the scanning irradiation system. The number of combinations of beam properties to measure for the commissioning is more than 7200, i.e., 201 energy steps, 3 intensities, and 12 gantry angles. To compress the commissioning time, quick and simple range verification system is required. In this work, the authors develop a quick range verification system using scintillator and charge-coupled device (CCD) camera and estimate the accuracy of the range verification. A cylindrical plastic scintillator block and a CCD camera were installed on the black box. The optical spatial resolution of the system is 0.2 mm/pixel. The camera control system was connected and communicates with the measurement system that is part of the scanning system. The range was determined by image processing. Reference range for each energy beam was determined by a difference of Gaussian (DOG) method and the 80% of distal dose of the depth-dose distribution that were measured by a large parallel-plate ionization chamber. The authors compared a threshold method and a DOG method. The authors found that the edge detection method (i.e., the DOG method) is best for the range detection. The accuracy of range detection using this system is within 0.2 mm, and the reproducibility of the same energy measurement is within 0.1 mm without setup error. The results of this study demonstrate that the authors' range check system is capable of quick and easy range verification with sufficient accuracy.

TH-CD-BRA-07: Range Verification System Using Scintillator and CCD Camera for the Scanning Irradiation System

Purpose: To compress the quality assurance time for the scanned carbon-ion beam system, we have been developed the novel range verification system using scintillator and CCD (charge-coupled device) camera. Methods: A cylindrical plastic scintillator block and a CCD camera were installed on the black box. The range was determined by image processing. Reference range for each energy beam was determined the 80 percent of distal dose of the depth dose distribution that were measured by a large parallel-plate ionization chamber. Carbon beams ranging from 151.9 to 430 MeV/n were tested and compared with reference range. The common reference point of range is distal 80% of the dose distribution. In order to select the best reference point on a light distribution, the authors compared two range detection. Methods: threshold method (TH); the threshold positions set by the range from 10 to 90% of maximum value on the projected line are identified and difference of Gaussian (DOG) method. Using DOG method, range position is determined by zero-crossing position in the difference between small-Gaussian smoothed data and large-Gaussian smoothed data. Results: The 1 mm range difference was clearly detected. Standard deviation of discrepancy from the range measured by the ionization chamber was less than 0.1 mm. A 1 mm setup error in the any direction was less than 0.2 mm range error. Conclusion: We have shown that the range of carbon beam can be determined with sub-millimeter accuracy using scintillator and CCD camera. The 80 percent of maximum value is minimized discrepancies between expected and measured ranges for carbon beam. It was supposed to be a Result of the change of shape due to quenching effect. Since the system determine the range with short time and sufficient accuracy, it seems be that the system has potential to play the daily range check system.

Application of WLS strips for position determination in strip PET tomograph based on plastic scintillators

Abstract A method of the determination of a γ-quantum absorption point in a plastic scintillator block using a matrix of wavelength-shifting (WLS) strips is proposed. An application of this method for the improvement of position resolution in newly proposed positron emission tomography (PET) detectors based on plastic scintillators is presented. The method enables to reduce parallax errors in the reconstruction of images, which occurs in the presently used PET scanners.

Preliminary investigations on the determination of three-dimensional dose distributions using scintillator blocks and optical tomography

Clinical QA in teletherapy as well as the characterization of experimental radiation sources for future medical applications requires effective methods for measuring three-dimensional (3D) dose distributions generated in a water-equivalent medium. Current dosimeters based on ionization chambers, diodes, thermoluminescence detectors, radiochromic films, or polymer gels exhibit various drawbacks: High quality 3D dose determination is either very sophisticated and expensive or requires high amounts of effort and time for the preparation or read out. New detectors based on scintillator blocks in combination with optical tomography are studied, since they have the potential to facilitate the desired cost-effective, transportable, and long-term stable dosimetry system that is able to determine 3D dose distributions with high spatial resolution in a short time. A portable detector prototype was set up based on a plastic scintillator block and four digital cameras. During irradiation the scintillator emits light, which is detected by the fixed cameras. The light distribution is then reconstructed by optical tomography, using maximum-likelihood expectation maximization. The result of the reconstruction approximates the 3D dose distribution. First performance tests of the prototype using laser light were carried out. Irradiation experiments were performed with ionizing radiation, i.e., bremsstrahlung (6 to 21 MV), electrons (6 to 21 MeV), and protons (68 MeV), provided by clinical and research accelerators. Laser experiments show that the current imaging properties differ from the design specifications: The imaging scale of the optical systems is position dependent, ranging from 0.185 mm/pixel to 0.225 mm/pixel. Nevertheless, the developed dosimetry method is proven to be functional for electron and proton beams. Induced radiation doses of 50 mGy or more made 3D dose reconstructions possible. Taking the imaging properties into account, determined dose profiles are in agreement with reference measurements. An inherent drawback of the scintillator is the nonlinear light output for high stopping-power radiation due to the quenching effect. It impacts the depth dose curves measured with the dosimeter. For single Bragg peak distributions this leads to a peak to plateau ratio of 2.8 instead of 4.5 for the reference ionization chamber measurement. Furthermore, the transmission of the clinical bremsstrahlung beams through the scintillator leads to the saturation of one camera, making dose reconstructions in that case presently not feasible. It is shown that distributions of scintillation light generated by proton or electron beams can be reconstructed by the dosimetry system within minutes. The quenching apparent for proton irradiation, and the yet not precisely determined position dependency of the imaging scale, require further investigation and corrections. Upgrading the prototype with larger or inorganic scintillators would increase the detectable proton and electron energy range. The presented results show that the determination of 3D dose distributions using scintillator blocks and optical tomography is a promising dosimetry method.

Atmospheric dependence of the stopping cosmic ray muon rate at ground level

The rate of low energy (≲ 150 MeV) cosmic ray muons was measured at ground level as a function of several atmospheric parameters. Stopped muons were detected in a plastic scintillator block and correlations were determined using a linear regression model. A strong anti-correlation between fractional changes in the ground-level pressure and the stopping muon rate of −3.0 ± 0.5 was found, and also a −4.1 ± 0.5 anti-correlation with the fractional change in atmospheric height at 10 kPa pressure. A weak positive correlation with the 10 kPa temperature was also found, but it was shown not to be statistically significant in our data set. The same analysis was applied to the total rate of all charged cosmic ray particles detected with the same apparatus, and good agreement with previous work was seen. The pressure and height correlation parameters for stopping muons are larger than for the total rate of all charged particles by factors of about 1.6 and 3.7, respectively.

New method for obtaining position and time structure of source in HDR remote afterloading brachytherapy unit utilizing light emission from scintillator

When using a HDR remote afterloading brachytherapy unit, results of treatment can be greatly influenced by both source position and treatment time. The purpose of this study is to obtain information on the source of the HDR remote afterloading unit, such as its position and time structure, with the use of a simple system consisting of a plastic scintillator block and a charge‐coupled device (CCD) camera. The CCD camera was used for recording images of scintillation luminescence at a fixed rate of 30 frames per second in real time. The source position and time structure were obtained by analyzing the recorded images. For a preset source‐step‐interval of 5 mm, the measured value of the source position was 5.0±1.0mm, with a pixel resolution of 0.07 mm in the recorded images. For a preset transit time of 30 s, the measured value was 30.0±0.6 s, when the time resolution of the CCD camera was 1/30 s. This system enabled us to obtain the source dwell time and movement time. Therefore, parameters such as I192r source position, transit time, dwell time, and movement time at each dwell position can be determined quantitatively using this plastic scintillator‐CCD camera system.PACS number: 87.53.Jw

PHOTON – An optical Monte Carlo code for simulating scintillation detector responses

A Monte Carlo code, PHOTON, has been developed to simulate optical photon transport in scintillation detectors. The code supports arbitrarily complex geometry models, flexible models for material and surface properties specification, detailed treatment of complex refractive index materials, thin-film surface coatings and interactive simulation with graphical display. This paper concentrates on the photon transport simulation and a simple benchmarking study, comparing the experimental and calculated light yields from a rectangular plastic scintillator block.

Development of an easy-to-handle range measurement tool using a plastic scintillator for proton beam therapy

Proton beam therapy can concentrate the dose on a tumour. In order to offer high-precision proton beam therapy to the patient, it is important to confirm the range every day. At the National Cancer Center Hospital East (NCC), the range measurement tool consists of a water phantom and an ionization chamber. These large and heavy tools take a long time to set up. Therefore, we developed a simple and easy-to-handle range measurement tool for proton beam therapy. This tool consists of a plastic scintillator block and a CCD camera. We recorded visible scintillation light generated by proton irradiation on the scintillator, and could measure the range from the shape of light distribution by using a computer with automatic analysis software installed. We carried out proton irradiation experiments with this tool to examine its performance as a tool of daily range measurements. The precision of the range measurement is within 0.3 mm (sd). The tool can measure possible short-term range variation with 1 s sampling time during the time interval of a typical treatment in a few minutes. We conclude that this tool can measure the range with sufficient resolution in a short time, and is useful for range control in a clinical setting.

Simple range measurement of therapeutic ion beams using visible rays generated in a bare plastic scintillator block

In ion-beam therapy, it is necessary to measure the range of the beams in a tissue-equivalent material. We demonstrate a simple method for the range measurement, using a bare plastic scintillator block and a CCD camera. This method presents an instant result for the range measurement of the therapeutic ion beams. The linearity, resolution and application of the method are discussed.

Direct detection of particle tracks in a scintillator block with a lens system coupled to an image intensifier

Images of photons emitted in a scintillator block were recorded directly with an optical lens system and readout optoelectronics comprising image intensifiers and a CCD camera. The viewed area of the scintillator block was 28×27 mm 2. The performance of the system was studied by detecting tracks of cosmic rays and an electron beam. For a CsI(TI) crystal and a plastic scintillator block, the linear densities of light spots along the track were 1.34±0.07 and 0.19±0.02 mm −1 . When the irradiated depth of the blocks was limited to 20 mm, the spatial resolutions of the spot obtained for these cases were 0.65±0.08 and 0.47±0.05 mm , respectively.

Plastic scintillator block as photon beam monitor for EGRET calibration

The EGRET (Energetic Gamma Ray Experiment Telescope) detector has been calibrated at SLAC (Stanford Linear Accelerator) and, to a lesser degree, at the MIT (Massachusetts Institute of Technology) Bates Linear Accelerator Center. To monitor the photon beams for the calibration, a plastic scintillator block, 5 cm*5 cm in cross section, 15 cm in length, and viewed by a single photomultiplier tube, was used for the entire beam energy range of 15 MeV to 10 GeV. The design operation, and method of analysis of the beam intensity are presented. A mathematical framework has been developed to treat the general case of a beam with multiphoton beam pulses and with a background component. A procedure to deal with the fluctuations of the beam intensity over a data-taking period was also developed. The photon beam monitor is physically sturdy, electronically steady, simple to construct, and easy to operate. Its major merits lie in its sheer simplicity of construction and operation and in the wide energy range it can cover.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A compton-suppressed low level gamma-ray scintillation spectrometer for the samples of extended geometry

A Compton-suppressed gamma-ray scintillation spectrometer having high sensitivity and selectivity has been described. The spectrometer is intended to be used for the identification and estimation of low levels of gamma radioactivity in a broad range of sample sizes containing a moderately compelx mixture of gamma-emiting radionuclides. The spectrometer uses a 7.6 cm dia.×76. cm thick Nal(TI) detector having anticoincidence guard of a rectangular plastic scintillator block of size 38 cm×38 cm×30 cm placed inside u 15 cm thick lead shield. Various details of the setup are given and the use of such a system for the analysis of complex spectra of low level activity has been discussed. The anticoincidence guard provides a gross background reduction by a factor of 2.8 for the energy interval between 50 keV and 1600 keV. Performance evaluation of the system with respect to background reduction. Compton suppression factor, peak/total ratio and peak prominance factor have been discussed.

Radiocontamination of the environment and its effects on the mother and fetus—III: Part II—Retention of cesium 137 by pregnant women, placentae and infants

The total body counter employed in this study has bccn presented elsewhere cz~) and consists of four large plastic scintillator units, each block measuring 50/50/15 cm, placed at 30 cm over a Lucite plate counting bed at equal distances. A similar arrangement with four other scintillation blocks was placed 10 cm below the counting plastic bed. Each plastic scintillator block was optically linked with a photomultiplicr of 5 in. dia; the ratio between the photocathodc area of the photomultiplicr and the scintillation block is about 5 per cent, which diminishes the efficiency of the system. The combined output from the units reached a cathode follower and wcrc mixed and passed to a linear amplifier. The output of the amplifier was further fed into three single-channel analyzers with associated sealers. For the potassium 40 peak (1455kcV) two singlechannel analyzers selected the pulse, each of the analyzers being set at half of the peak; the sum of the two pulses was attributed to 40 K, while the third analyzer was adjusted to the photopeak of a~Cs. The counting system was calibrated by body phantoms of a wide variety of lengths and weights, filled with distilled water containing a known amount of KC1 or 137Cs. The calibration constants were found to show a linear relationship with the body weight between 36 and 70 kg; the correction was made for the weights of the subjects measured. The sensitivity of the instruments was controlled by counting 18~Cs point sources. Fifteen minutes counts wcrc made on each subject; the background level was periodically measured throughout the day for I hr. The data wcrc processed by a digital computer (Burroughs-5500): with a counting time of 15m in, the statistical accuracy (q-a) was respectively -4-1.5 and 4-65 per cent for 40 K and 137Cs, assuming a body burden of 150 g stable potassium and 10 nc aXVCs. However, the absolute uncertainties arising from calculation errors may amount to 4-5 per cent.

The detection efficiency of a plastic scintillator for neutrons in the energy range of 21–29 MeV

A method of calibrating the efficiency of a high-energy neutron detector is described. Results are given for a plastic scintillator block, in the region 21–29 MeV. Comparison with results from other laboratories shows that, with a proton energy detection threshold of about 4 MeV, and for linear dimensions not too much smaller than the range of the maximum energy protons, the efficiency is rather independent of the size or shape of the scintillator and equal to nearly 2% per centimetre thickness in the range 10–30 MeV.