Inorganic Scintillator Detectors Research Articles

In vivo dosimetry with an inorganic scintillation detector during multi-channel vaginal cylinder pulsed dose-rate brachytherapy: Dosimetry for pulsed dose-rate brachytherapy

Background and purposeIn vivo dosimetry is not standard in brachytherapy and some errors go undetected. The aim of this study was to evaluate the accuracy of multi-channel vaginal cylinder pulsed dose-rate brachytherapy using in vivo dosimetry. Materials and methodsIn vivo dosimetry data was collected during the years 2019–2022 for 22 patients (32 fractions) receiving multi-channel cylinder pulsed dose-rate brachytherapy. An inorganic scintillation detector was inserted in a cylinder channel. Each fraction was analysed as independent data sets. In vivo dosimetry-based source-tracking was used to determine the relative source-to-detector position. Measured dose was compared to planned and re-calculated source-tracking based doses. Assuming no change in organ and applicator geometry throughout treatment, the planned and source-tracking based dose distributions were compared in select volumes via γ-index analysis and dose-volume-histograms. ResultsThe mean ± SD planned vs. measured dose deviations in the first pulse were 0.8 ± 5.9 %. In 31/32 fractions the deviation was within the combined in vivo dosimetry uncertainty (averaging 9.7 %, k = 2) and planning dose calculation uncertainty (1.6 %, k = 2). The dwell-position offsets were < 2 mm for 88 % of channels, with the largest being 5.1 mm (4.0 mm uncertainty, k = 2). 3 %/2 mm γ pass-rates averaged 97.0 % (clinical target volume (CTV)), 100.0 % (rectum), 99.9 % (bladder). The mean ± SD deviation was −1.1 ± 2.9 % for CTV D98, and −0.2 ± 0.9 % and −1.2 ± 2.5 %, for bladder and rectum D2cm3 respectively, indicating good agreement between intended and delivered dose. ConclusionsIn vivo dosimetry verified accurate and stable dose delivery in multi-channel vaginal cylinder based pulsed dose-rate brachytherapy.

Cerenkov free micro-dosimetry in small-field radiation therapy technique

Objective. Optical fiber-based scintillating dosimetry is a recent promising technique owing to the miniature size dosimeter and quality measurement in modern radiation therapy treatment. Despite several advantages, the major issue of using scintillating dosimeters is the Cerenkov effect and predominantly requires extra measurement corrections. Therefore, this work highlighted a novel micro-dosimetry technique to ensure Cerenkov-free measurement in radiation therapy treatment protocol by investigating several dosimetric characteristics. Approach. A micro-dosimetry technique was proposed with the performance evaluation of a novel infrared inorganic scintillator detector (IR-ISD). The detector essentially consists of a micro-scintillating head based on IR-emitting micro-clusters with a sensitive volume of 1.5 × 10−6 mm3. The proposed system was evaluated under the 6 MV LINAC beam used in patient treatment. Overall measurements were performed using IBATM water tank phantoms by following TRS-398 protocol for radiotherapy. Cerenkov measurements were performed for different small fields from 0.5 × 0.5 cm2 to 10 × 10 cm2 under LINAC. In addition, several dosimetric parameters such as percentage depth dose (PDD), high lateral resolution beam profiling, dose linearity, dose rate linearity, repeatability, reproducibility, and field output factor were investigated to realize the performance of the novel detector. Main results. This study highlighted a complete removal of the Cerenkov effect using a point-like miniature detector, especially for small field radiation therapy treatment. Measurements demonstrated that IR-ISD has acceptable behavior with dose rate variability (maximum standard deviation ∼0.18%) for the dose rate of 20–1000 cGy s−1. An entire linear response (R 2 = 1) was obtained for the dose delivered within the range of 4–1000 cGy, using a selected field size of 1 × 1 cm2. Perfect repeatability (max 0.06% variation from average) with day-to-day reproducibility (0.10% average variation) was observed. PDD profiles obtained in the water tank present almost identical behavior to the reference dosimeter with a build-up maximum depth dose at 1.5 cm. The small field of 0.5 × 0.5 cm2 profiles have been characterized with a high lateral resolution of 100 µm. Significance. Unlike recent plastic scintillation detector systems, the proposed micro-dosimetry system in this study requires no Cerenkov corrections and showed efficient performance for several dosimetric parameters. Therefore, it is expected that considering the detector correction factors, the IR-ISD system can be a suitable dose measurement tool, such as in small-field dose measurements, high and low gradient dose verification, and, by extension, in microbeam radiation and FLASH radiation therapy.

Determination of intrinsic energy dependence of point-like inorganic scintillation detector in brachytherapy.

Inorganic scintillation detectors (ISDs) are promising for in vivo dosimetry in brachytherapy (BT). ISDs have fast response, providing time resolved dose rate information, and high sensitivity, attributed to high atomic numbers. However, the conversion of the detector signal to absorbed dose-to-water is highly dependent on the energy spectrum of the incident radiation. This dependence is comprised of absorbed dose energy dependence, obtainable with Monte Carlo (MC) simulation, and the absorbed dose-to-signal conversion efficiency or intrinsic energy dependence requiring measurements. Studies have indicated negligible intrinsic energy dependence of ZnSe:O-based ISDs in Ir-192 BT. A full characterization has not been performed earlier. This study characterizes the intrinsic energy dependence of ZnSe:O-based ISDs for kV X-ray radiation qualities, with energies relevant for BT. Three point-like ISDs made from fiber-coupled cuboid ZnSe:O-based scintillators were calibrated at the Swedish National Metrology Laboratory for ionizing radiation. The calibration was done in terms of air kerma free-in-air, , in 13 X-ray radiation qualities, , from 25 to 300 kVp (CCRI 25-250kV and ISO 4037 N-series), and in terms of absorbed dose to water, , in a Co-60 beam, . The mean absorbed dose to the ISDs, relative to and , were obtained with the MC code TOPAS (Geant4) using X-ray spectra obtained with SpekPy software and laboratory filtration data and a generic Co-60 source. The intrinsic energy dependence was determined as a function of effective photon energy, , (relative to Co-60). The angular dependence of the ISD signal was measured in a 25 kVp (0.20mm Al HVL) and 135 kVp beam (0.48mm Cu HVL), by rotating the ISDs 180° around the fiber's longitudinal axis (perpendicular to the beam). A full 360° was not performed due to setup limitations. The impact of detector design was quantified with MC simulation. Above 30keV the intrinsic energy dependence varied with less than 5±4% from unity for all detectors (with the uncertainty expressed as the mean of all expanded measurement uncertainties for individual above 30keV, k=2). Below 30keV, it decreased with up to 17% and inter-detector variations of 13% were observed, likely due to differences in detector geometry not captured by the simulations using nominal geometry. In the 25 kVp radiation quality, the ISD signal varied with 24% over a ∼45° rotation. For 135 kVp, the corresponding variation was below 3%. Assuming a 0.05mm thicker layer of reflective paint around the sensitive volume changed the absorbed dose with 6.3% at the lowest , and with less than 2% at higher energies. The study suggests that the ISDs have an intrinsic energy dependence relative to Co-60 lower than 5±4% in radiation qualities with >30keV. Therefore, they could in principle be calibrated in a Co-60 beam quality and transferred to such radiation qualities with correction factors determined only by the absorbed dose energy dependence obtained from MC simulations. This encourages exploration of the ISDs' applications in intensity modulated BT with Yb-169 or other novel intermediate energy isotopes.

Localising and identifying radionuclides via energy-resolved angular photon responses

A technique for the in-situ localisation of radioactivity is described whereby the energy-resolved angular photon response of a collimated inorganic scintillation detector is used to derive the spatial arrangement of a variety of radioactive source configurations. The influence of photon radiation (X- and γ ray) incident on the collimated detector is expressed mathematically, by way of a sinc transform embedded to a dynamic linear regression model, to increase the spatial accuracy of the localisation. This approach is tested experimentally with two pairs of like radionuclides, two pairs of different combinations of radionuclides and three different radionuclides to demonstrate its combined isotopic discrimination and spatial localisation capabilities. A fit based on the model referred to above is observed to reproduce the data for the combined X- and γ-ray regions of interest effectively. This allows for increased resolution via interpolation between the data which is observed to improve location accuracy significantly. This research is relevant to applications in autonomous robotic exploration tasks and for the characterisation of contaminated environments associated with nuclear legacies and radiological emergencies.

Investigation of specially designed bentonite samples as potential bricks with better radiation shielding properties

Bentonite clay, a naturally occurring very fine volcanic powder that lies mainly on the nano-scale, has been investigated during this study to assess the possibility of producing a brick with enhanced radiation shielding properties. Five samples were prepared based on natural bentonite and studied along with another three previously studied building bricks. Physical properties such as density and particle size distribution have been studied for bentonite clay before and after calcination and ball-milling. Radiation attenuation parameters, which assess shielding against both energetic photons and fast neutrons, were calculated theoretically employing specific friendly-user programs such as WinXCom, Auto-Zeff, NXCom, and MRCsC and other analytical calculations. Linear attenuation coefficients (μ) of bentonite samples were experimentally measured at 662 keV energy of Cs-137 and 1173 and 1332 keV energies of Co-60, gamma ray radioactive sources using NaI(Tl) inorganic scintillation detector. After that, a statistical comparison between theoretical and experimental (μ) values for all studied samples was conducted. It has been found that the density of the bentonite sample increases from 0.84 to 1.59 g/cm3 with calcination and pressing; moreover, ball-milled compressed calcined bentonite samples have shown promising γ-rays radiation shielding properties among the studied samples having (μ) values range between; 0.112–0.133 for Eγ equals 0.662 MeV, 0.090–0.110 for Eγ equals 1.173 MeV, and 0.087–0.105 for Eγ equals 1.332 MeV. Last but not least, an entire agreement between the theoretically obtained radiation attenuation parameters using the abovementioned tools and the experimentally measured ones is not a must, especially since other factors like average particle size and compression are not necessarily not considered upon using the tools above.

Characterization of Inorganic Scintillator Detectors for Dosimetry in Image-Guided Small Animal Radiotherapy Platforms.

The purpose of the study was to characterize a detection system based on inorganic scintillators and determine its suitability for dosimetry in preclinical radiation research. Dose rate, linearity, and repeatability of the response (among others) were assessed for medium-energy X-ray beam qualities. The response's variation with temperature and beam angle incidence was also evaluated. Absorbed dose quality-dependent calibration coefficients, based on a cross-calibration against air kerma secondary standard ionization chambers, were determined. Relative output factors (ROF) for small, collimated fields (≤10 mm × 10 mm) were measured and compared with Gafchromic film and to a CMOS imaging sensor. Independently of the beam quality, the scintillator signal repeatability was adequate and linear with dose. Compared with EBT3 films and CMOS, ROF was within 5% (except for smaller circular fields). We demonstrated that when the detector is cross-calibrated in the user's beam, it is a useful tool for dosimetry in medium-energy X-rays with small fields delivered by Image-Guided Small Animal Radiotherapy Platforms. It supports the development of procedures for independent "live" dose verification of complex preclinical radiotherapy plans with the possibility to insert the detectors in phantoms.

A study on relative neutron sensitivity of Yb:YAG with CSNS Back-n white neutron source

Two inorganic scintillator detectors consisting of Yb:YAG scintillators and photomultiplier tubes, and an oscilloscope were used to studied the neutron sensitivities of Yb:YAG scintillators at the China Spallation Neutron Source (CSNS) Back-n white neutron source. The relative neutron sensitivity curves of two Yb:YAG scintillators in the energy region between 0.5 and 20 MeV were obtained for the first time. As the measured relative neutron sensitivity curves of Yb:YAG scintillators cannot be verified by the Monte Carlo method and there was no referable data, the neutron sensitivity curve of a ST401 scintillator was also studied in the same method and a Geant4 simulation of ST401 scintillator was conducted to verify the experiment method in this paper. The result showed that the experimental and simulation results were approximately consistent between 17–20 MeV, and agreed well between 1–17 MeV. A comparison between the experimental result and references of ST401 scintillator was also applied and the result showed that the curve tendency of the experimental result and references was matched. The above results imply that the measured relative neutron sensitivity curves and the experimental method used herein were reliable. It also demonstrated the feasibility of studying the neutron sensitivity of inorganic scintillator based on the white neutron source.

A Novel Micro-Dosimetry Technique to Advance Small-Field Radiation Therapy Treatment

<h3>Purpose/Objective(s)</h3> Optical fiber-based scintillating dosimetry is the most recent promising technique in modern radiation therapy owing to the miniature size, high sensitivity, flat energy dependency, etc. Despite several advantages, the major issue of using scintillating dosimeters is the Cerenkov contamination and predominantly requires extra measurement corrections. Therefore, this work highlighted a novel micro-dosimetry technique to ensure Cerenkov-free measurement and quality treatment. <h3>Materials/Methods</h3> A micro-dosimetry technique was proposed based on a novel infrared inorganic scintillator detector (IR-ISD). The detector essentially consists of a micro-scintillating head with a sensitive volume of 1.5 × 10⁻⁶ mm³ integrated with optical fiber. The proposed system was evaluated under the 6/15 MV LINAC beam as well as 320KV- ¹⁹²Ir Brachytherapy (BT) source used in patient treatment. Overall measurements were performed using IBA^TM water tank phantoms by following TRS-398 protocol for radiotherapy and TG43U1 recommendations for BT. Cerenkov measurements were performed for different small fields from 0.5 × 0.5 cm² to 10 × 10cm² under LINAC as well as till 0.25cm distance from the BT source. In addition, several dosimetric parameters such as PDD, beam profiling, field output factor, dose linearity, dose rate linearity, repeatability, and scintillation stability were investigated to verify the device's performance. Finally, a comparative study is shown using Monte-Carlo (MC) simulation, reference dosimeters (microDiamond and film), and data from recent literature. <h3>Results</h3> This study highlighted a complete removal of the Cerenkov effect using a point-like miniatured detector, especially for small-field beam treatment. Measurements demonstrated that IR-ISD has acceptable behavior with dose rate variability (maximum standard deviation ∼ 0.15%) for the dose rate of 20 cGy/s to 1000 cGy/s. An entire linear response (R²=1) was obtained with the dose delivered in the range of 4cGy to 1000 cGy, independently of the field size selected from 4 × 4 cm² to 0.5 × 0.5 cm². Perfect repeatability (0.15 % variation from average) and day-to-day reproducibility (0.25% variation) was observed. PDD profiles present accurate dose distribution with almost identical behavior to the reference dosimeter and simulation results (<1.5% variation). The small field of 0.5 × 0.5 cm² profile (inline & crossline) has been measured to characterize convolution effect and source penumbra. Eventually, in BT, a comparison with MC simulations shows that measurement agrees within 0.65% till 0.25 cm source-to-detector distance. <h3>Conclusion</h3> Unlike recent PSD systems (e.g., exradin W1/W2), the proposed micro-dosimetry system requires no Cerenkov corrections and showed efficient performance for several dosimetric measurements. Therefore, the novel IR-ISD detector could be a quality tool for small-field dose verification (e.g., in SRS, SBRT, IMRT, etc.), intra-beam characterizations, and BT treatment plan.

Accelerated radiation transport modeling techniques for pencil beam computed tomography using gamma rays

Monte Carlo radiation transport modeling studies were performed for a compact, and high-resolution gamma-ray computed tomography system designed for imaging irradiated nuclear fuel. The system comprises a 60Co source – chosen for its highly penetrating 1173 keV and 1332 keV gamma rays – a pair of high-aspect-ratio pencil beam collimators, and an inorganic scintillator detector. Two acceleration methods are proposed to rapidly model a transmission type gamma-ray tomography system. The first, a variance reduction technique, is based on performing Monte Carlo simulations with a monodirectionally-biased source, sampled from a characteristic sub-volume of the full source volume. The second acceleration method is based on the deterministic calculations using the Beer–Lambert law and detector response characteristics. Comparison of simulations using acceleration approaches with analog simulations of the fully isotropic, full-volume equivalent, show that the Monte Carlo variance reduction technique gives quantitatively accurate predictions for large collimator aspect ratios while the deterministic calculations are semi-quantitative but converge close to the correct result as the collimator aspect ratio increases. As such, these techniques can be used to reduce the computational cost in generating simulated radiographs and tomographs by several orders of magnitude. Experimental validation efforts are currently underway and will be demonstrated in future work.

Calculation of the Effective Energy Release Centerʼs Position of Inorganic Scintillation Detectors for Calibration at Small “Source–Detector” Distances

Inorganic scintillation detectors are widely used to measure of dose rate in the environment due to their high sensitivity to photon radiation. A distinctive feature when using such detectors is the need to take into account of the position of the effective energy release center. This peculiarity is actual when using measuring instruments with inorganic scintillation detectors as working standards during calibration at short “source–detector” distances in conditions of low-background shield or using a facility with protection from external gamma radiation background in the dose rate range from 0.03 to 0.3 μSv/h (μGy/h). The purpose of this work was to calculate the position of the effective energy release center of NaI(Tl) scintillation detectors and to take it into account when working at short “source–detector” distances.An original method of determining the position of the effective energy release center when irradiating the side and end surfaces of inorganic scintillation detector with parallel gamma radiation flux and point gamma radiation sources at small “source–detector” distances using Monte Carlo methods is proposed. The results of calculations of the position of the effective energy release center of NaI(Tl) based detectors of “popular” sizes for the cases of parallel gamma radiation flux and point sources of gamma radiation at small “source–detector” distances are presented. The functional dependences of the position of the effective energy release center of NaI(Tl) based detectors on the distance to the point gamma radiation sources and the energy of gamma radiation sources are presented.As a result of the study it was found that for scintillation NaI(Tl) detectors of medium size (for example, Ø25×40 mm or Ø40×40 mm) the point gamma radiation source located at a distance of 1 m or more, creates a radiation field which does not differ in characteristics from the radiation field created by a parallel flux of gamma radiation. It is shown that approaching the point gamma radiation source to the surface of scintillation detector leads to displacement of the position of the effective energy release center to the surface of the detector.

Geant4 ile İnorganik Kristal Sintilatörler için Enerji Çözünürlüğünün Reflektör Malzemesine Bağımlılığı Üzerine Çalışma

The scintillator has played a primary role as the ideal device for the detection and measurement of particles and radiation in modern physics. With the development of experimental physics, the demand for new improved scintillating materials for several types of applications has kept increasing. High efficiency, fast scintillation and good energy resolution are among the most desired specifications as to a good scintillator. Yet, a variety of scintillators can be preferred depending on the precise specifications of the application considered. If the case is that the detection of gamma rays and high-energy electrons or positrons, inorganic crystals are exceptionally suitable scintillator because highly intense light outputs and the strong stopping power enable these type of crystals to provide better energy resolution among all scintillators. In this study, a scintillation detector consisting of inorganic crystal scintillator material (NaI:Tl and CsI:Tl) was modeled with the help of Geant4 scientific toolkit to determine if the energy resolution of the inorganic crystal scintillator detector is dependent on crystalline size and reflector material. In each simulation, different sized crystal covered with a variety of reflector type was exposed to the same energy gamma radiation; the resulting energy spectrum was evaluated and compared to others obtained.

Miniaturized scintillator dosimeter for small field radiation therapy

The concept of a miniaturized inorganic scintillator detector is demonstrated in the analysis of the small static photon fields used in external radiation therapy. Such a detector is constituted by a 0.25 mm diameter and 0.48 mm long inorganic scintillating cell (1.6 × 10−5 cm3 detection volume) efficiently coupled to a narrow 125 μm diameter silica optical fiber using a tiny photonic interface (an optical antenna). The response of our miniaturized scintillator detector (MSD) under 6 MV bremsstrahlung beam of various sizes (from 1 × 1 cm2 to 4 × 4 cm2) is compared to that of two high resolution reference probes, namely, a micro-diamond detector and a dedicated silicon diode. The spurious Cerenkov signal transmitted through our bare detector is rejected with a basic spectral filtering. The MSD shows a linear response regarding the dose, a repeatability within 0.1% and a radial directional dependence of 0.36% (standard deviations). Beam profiling at 5 cm depth with the MSD and the micro-diamond detector shows a mismatch in the measurement of the full widths at 80% and 50% of the maximum which does not exceed 0.25 mm. The same difference range is found between the micro-diamond detector and a silicon diode. The deviation of the percentage depth dose between the MSD and micro-diamond detector remains below 2.3% within the first fifteen centimeters of the decay region for field sizes of 1 × 1 cm2, 2 × 2 cm2 and 3 × 3 cm2 (0.76% between the silicon diode and the micro-diamond in the same field range). The 2D dose mapping of a 0.6 × 0.6 cm2 photon field evidences the strong 3D character of the radiation-matter interaction in small photon field regime. From a beam-probe convolution theory, we predict that our probe overestimates the beam width by 0.06%, making our detector a right compromise between high resolution, compactness, flexibility and ease of use. The MSD overcomes problem of volume averaging, stem effects, and despite its water non-equivalence it is expected to minimize electron fluence perturbation due to its extreme compactness. Such a detector thus has the potential to become a valuable dose verification tool in small field radiation therapy, and by extension in Brachytherapy, FLASH-radiotherapy and microbeam radiation therapy.

OC-0110 Characterisation of an inorganic scintillation detector system for time resolved in vivo dosimetry

OC-0110 Characterisation of an inorganic scintillation detector system for time resolved in vivo dosimetry

High resolution small-scale inorganic scintillator detector: HDR brachytherapy application.

Brachytherapy (BT) deals with high gradient internal dose irradiation made up of a complex system where the source is placed nearby the tumor to destroy cancerous cells. A primary concern of clinical safety in BT is quality assurance to ensure the best matches between the delivered and prescribed doses targeting small volume tumors and sparing surrounding healthy tissues. Hence, the purpose of this study is to evaluate the performance of a point size inorganic scintillator detector (ISD) in terms of high dose rate brachytherapy (HDR-BT) treatment. A prototype of the dose verification system has been developed based on scintillating dosimetry to measure a high dose rate while using an 192 Ir BT source. The associated dose rate is measured in photons/s employing a highly sensitive photon counter (design data: 20 photons/s). Dose measurement was performed as a function of source-to-detector distance according to TG43U1 recommendations. Overall measurements were carried out inside water phantoms keeping the ISD along the BT needle; a minimum of 0.1cm distance was maintained between each measurement point. The planned dwell times were measured accurately from the difference of two adjacent times of transit. The ISD system performances were also evaluated in terms of dose linearity, energy dependency, scintillation stability, signal-to-noise ratio (SNR), and signal-to-background ratio (SBR). Finally, a comparison was presented between the ISD measurements and results obtained from TG43 reference dataset. The detection efficiency of the ISD was verified by measuring the planned dwell times at different dwell positions. Measurements demonstrated that the ISD has a perfectly linear behavior with dose rate (R2 =1) and shows high SNR (>35) and SBR (>36) values even at the lowest dose rate investigated at around 10cm from the source. Standard deviation (1σ) remains within 0.03% of signal magnitude, and less than 0.01% STEM signal was monitored at 0.1cm source-to-detector distance. Stability of 0.54% is achieved, and afterglow stays less than 1% of the total signal in all the irradiations. Excellent symmetrical behavior of the dose rate regarding source position was observed at different radiation planes. Finally, a comparison with TG-43 reference dataset shows that corrected measurements agreed with simulation data within 1.2% and 1.3%, and valid for the source-to-detector distance greater than 0.25cm. The proposed ISD in this study anticipated that the system could be promoted to validate with further clinical investigations. It allows an appropriate dose verification with dwell time estimation during source tracking and suitable dose measurement with a high spatial resolution both nearby (high dose gradient) and far (low dose gradient) from the source position.

Simultaneous, Robot-Compatible γ-Ray Spectroscopy and Imaging of an Operating Nuclear Reactor

The design and test of a robot-compatible, radiation detection instrument providing simultaneous $\gamma $ -ray imaging and $\gamma $ -ray spectroscopy is described. The sensing system comprises a cerium bromide inorganic scintillation detector and a cylindrical, lead slot collimator that is configured with a robot-compatible, on-board data acquisition system. The mount for the sensor is a lightweight, bespoke 3-axis gimbal actuated by servos for pan, tilt and rotation of the collimator for imaging capability. This paper discusses the integration of this relatively low-cost radiation detection apparatus with a commercially available, Robot-Operating-System-controlled robotic platform (a Clearpath Robotics™ Jackal). The detection system is compliant with the power and mass payload constraints of the robot. Its performance has been evaluated by means of two practical examples: a) measurements in a laboratory environment to assess the ability of the system to resolve two caesium-137 point sources, and b) deployment at the Jožef Stefan Institute TRIGA Mark II research reactor to assess the ability of the system to characterise the $\gamma $ -ray emission at 1 kW from a horizontal tangential beam port in the reactor hall and from the reactor sample pool above the core.

Development of an efficient technique for constructing energy spectrum of NaI(Tl) detector using spectrum of NE102 detector based on supervised model-free methods

The motivation of this study is development of a technique to construct energy spectrum of higher price/high resolution detectors (e.g. NaI (Tl)) using spectrum of lower price/low resolution detectors (e.g. NE102). Since there is no explicit mathematical model between these type of detectors (i.e. organic and inorganic scintillator detectors), it is necessary to utilize model-free methods. Construction of mapping function to generate spectrum of inorganic scintillator using spectrum of organic scintillator can be done by supervised model-free methods. Different supervised learning methods including localized neural networks, statistical methods, feed-forward neural networks, and conditional methods are utilized for spectrum construction. Experimental spectrums of the different radioisotopes (i.e. Co-60, Cs-137, Na-22, Am-241) including 15 spectrums of NaI (Tl) detector and 15 spectrums of NE102 detector are respectively used as training data and test data in the supervised methods. Results demonstrate that localized network (i.e. radial basis network) is the more appropriate method for the spectrum construction. The results of statistical method (i.e. support vector machine) is acceptable while conditional method (i.e. decision tree) does not give acceptable results and multi-layer perceptron does not learn the spectrums. The developed technique can be applied with an interesting ratio of training set to test set (i.e. r/(2r-1-r)). In other words, constructing spectrums of all possible combinations of r radioisotopes (i.e. 2r-1-r) is possible only with training of single radioisotopes spectrums (i.e. r). The developed method for generation of spectrums is more appropriate for identification of the radioisotopes and is not so useful for spectrum tracking. Spectrum tracking can be done by training of supervised learning method using generated pulses of detector.

High spatial resolution inorganic scintillator detector for high-energy X-ray beam at small field irradiation.

PurposeSmall field dosimetry for radiotherapy is one of the major challenges due to the size of most dosimeters, for example, sufficient spatial resolution, accurate dose distribution and energy dependency of the detector. In this context, the purpose of this research is to develop a small size scintillating detector targeting small field dosimetry and compare its performance with other commercial detectors.MethodAn inorganic scintillator detector (ISD) of about 200 µm outer diameter was developed and tested through different small field dosimetric characterizations under high‐energy photons (6 and 15 MV) delivered by an Elekta Linear Accelerator (LINAC). Percentage depth dose (PDD) and beam profile measurements were compared using dosimeters from PTW namely, microdiamond and PinPoint three‐dimensional (PP3D) detector. A background fiber method has been considered to quantitate and eliminate the minimal Cerenkov effect from the total optical signal magnitude. Measurements were performed inside a water phantom under IAEA Technical Reports Series recommendations (IAEA TRS 381 and TRS 483).ResultsSmall fields ranging from 3 × 3 cm2, down to 0.5 × 0.5 cm2 were sequentially measured using the ISD and commercial dosimeters, and a good agreement was obtained among all measurements. The result also shows that, scintillating detector has good repeatability and reproducibility of the output signal with maximum deviation of 0.26% and 0.5% respectively. The Full Width Half Maximum (FWHM) was measured 0.55 cm for the smallest available square size field of 0.5 × 0.5 cm2, where the discrepancy of 0.05 cm is due to the scattering effects inside the water and convolution effect between field and detector geometries. Percentage depth dose factor dependence variation with water depth exhibits nearly the same behavior for all tested detectors. The ISD allows to perform dose measurements at a very high accuracy from low (50 cGy/min) to high dose rates (800 cGy/min) and was found to be independent of dose rate variation. The detection system also showed an excellent linearity with dose; hence, calibration was easily achieved.ConclusionsThe developed detector can be used to accurately measure the delivered dose at small fields during the treatment of small volume tumors. The author's measurement shows that despite using a nonwater‐equivalent detector, the detector can be a powerful candidate for beam characterization and quality assurance in, for example, radiosurgery, Intensity‐Modulated Radiotherapy (IMRT), and brachytherapy. Our detector can provide real‐time dose measurement and good spatial resolution with immediate readout, simplicity, flexibility, and robustness.

Constructing energy spectrum of inorganic scintillator based on plastic scintillator by different kernel functions of SVM learning algorithm and TSC data mapping

In this paper, a novel idea is developed to construct energy spectrum of inorganic scintillator detector (e.g. NaI(Tl)) using energy spectrum of organic scintillator detector (e.g. NE102) by means of a model-free method. For this purpose, support vector machine (SVM) accompanied with different kernel functions (i.e. linear, polynomial, and Gaussian) is applied. The spectra of NE102 and NaI(Tl) detectors of the single radioisotopes (i.e. Co60, Cs137, Na22, and Am241) are utilized for training of SVM. In other words, data of NE102 detector are input spectrums of training patterns and data of NaI(Tl) detector are target spectrums of training patterns. To construct an appropriate mapping function between spectrums of detectors, a kind of cross-correlation technique namely mapping of totality of channels to single channel (TSC) is utilized. In the test process, spectrums of different combinations of the target radioisotopes are constructed and the results are compared with the measured spectrums. Polynomial kernel function gives good results. Linear and Gaussian kernel functions do not give so appropriate results. The major advantages of the developed method are: 1- The NaI(Tl) spectrums of different combinations of the target radioisotopes are constructed only by training of single radioisotopes spectrums. 2- Energy spectrums of high price/ high resolution detectors (i.e. inorganic scintillator detectors) can be constructed using low price/ low resolution detectors (i.e. plastic scintillator detectors). 3- This method can be used to construct energy spectrum of any type of inorganic scintillator (e.g. BGO detector) using either plastic or liquid scintillators. Liquid scintillator detectors (e.g. NE213) are more appropriate for detection/identification of radioactive sources which emit both gamma and neutron radiations. However, these detectors give low resolution gamma spectrums. The developed method can be appropriate for construction of higher resolution gamma spectrums for this type of sources. This application of the developed method is discussed in the manuscript.

Benchmarking a novel inorganic scintillation detector for applications in radiation therapy

PurposeThe aim of this study was to investigate the contribution of Cerenkov radiation to the overall signal measured with a novel inorganic scintillating detector (ISD). MethodsAn ISD based on terbium doped gadolinium oxysulphide (Gd2O2S:Tb) was used. A hyperspectral technique separated the Cerenkov signal from the radioluminescence (RL) signal of the ISD. The relative contribution of Cerenkov radiation was evaluated under different conditions. The efficiency of using simple spectral correction to reduce the Cerenkov contribution was quantified. Other experiments investigated were the dose-per-pulse dependence observed in our previous study and the absorbed-dose energy dependence when acquiring percentage depth dose curves using Monte Carlo (MC) simulations. ResultsThe maximum relative contribution of Cerenkov radiation was 2.10% for a 10 × 10 cm2 field at 10 cm depth. However, this percentage increased to 24% when the ISD was 7 cm out of field and exposed to a 10 × 10 cm2 field. Using 15 nm and 5 nm band-pass filters reduced the Cerenkov contribution across all experimental conditions by a maximum of 75% and 82%, respectively. The MC simulation results show discrepancies between the measured and simulated PDD profiles using the Gd2O2S:Tb scintillator at depth. ConclusionThis study showed that while Gd2O2S:Tb ISD provides high-signal intensity, the contribution of Cerenkov radiation under specific conditions can be significant. However, narrow band-pass filters can reduce the Cerenkov signal to a negligible level. The MC simulations suggest mechanisms other than the stem effect and the absorbed-dose energy dependence influence the response of the Gd2O2S:Tb scintillator measurements at depth.

Modern African nuclear detector laboratory

The upcoming detector facility aims at developing new state-of-the-art particle detectors as well as providing hands-on training to postgraduate students using both analog and digital signal processing from nuclear radiation detectors. The project is two-fold and aims at developing: 1) ancillary detectors to be coupled with the new GAMKA array at iThemba LABS. Of particular interest to our group is the determination of nuclear shapes, which depend on the hyperfine splitting of magnetic substates; 2) PET scanners for cancer imaging using a cheaper technology. Performance of NaI(Tl) inorganic scintillator detectors has been evaluated using PIXIE-16 modules from XIA digital electronics. Gamma-ray energy spectra were acquired from 60Co and 137Cs radioactive sources to calculate the detector resolution as well as to optimize the digital parameters. The present study focuses on improving and optimizing the slow and fast filter parameters for NaI(Tl) detectors which can eventually be used in the list mode of data aquisition.