Prompt Gamma Research Articles

Matrix effects corrections in prompt gamma-ray spectra of a PGNAA online analyzer system using artificial neural network

One of the well-known online monitoring techniques used for quality control of bulk samples is Prompt Gamma Neutron Activation Analysis (PGNAA). PGNAA suffers from the so-called matrix effect problems such as density, thickness and moisture content of the sample under study. In this work, an Artificial Neural Network (ANN) model is introduced to deal with these effects. The required spectra for training and testing the proposed ANN model are obtained by Monte Carlo simulation of the gamma-ray spectra recorded in a PGNAA online analyzer system used in cement factories. The gamma-ray spectra related to given set of density, thickness and moisture content are corrected channel-to-channel using the proposed ANN model. The corrected spectra are then compared against the standard spectra obtained for predefined standard density, thickness and moisture content. The improvement in Theil coefficient is larger than 70% for the tested spectra.

Characterization of Neutron and Gamma Beams at the TRIGA 2000 Reactor Beam Ports Using Monte Carlo

Neutron and gamma beams characterization at the beam ports of TRIGA 2000 reactor was done in order to prepare the development of Prompt Gamma Neutron Activation Analysis (PGNAA) facility. Characterization was performed by simulation using Monte Carlo method with MCNPX and PHITS computer codes. The MCNPX code is used to simulate the neutron-gamma fluence and spectra of the reactor core from fission reactions. The PHITS code is used to simulate the distribution of the neutron-gamma fluence in the beam ports. The simulation was done by modeling the geometry and elemental composition of reactor material and radiation source model in the form of fission reaction in the reactor core. This results will be used to select the most suitable one of the four beam ports for the PGNAA use, based on the prescribed requirements, such as the neutron spectral characteristics and neutron-gamma fluence ratio at the beam port’s outlet. The results indicate that the tangential beam port provides better characteristics of neutron spectrum and neutron-gamma fluence ratio so become most suitable for PGNAA facility.

GPU Accelerated Stochastic Origin Ensemble Method With List-Mode Data for Compton Camera Imaging in Proton Therapy

Proton beam therapy has the advantages over other forms of radiation therapy because it does less damage to healthy tissue while treating cancerous tissue. These advantages arise from the high dose deposition at the end of the proton beam which is known as the Bragg peak. This paper proposes a new architecture for graphics processing unit (GPU)-accelerated stochastic origin ensemble (SOE) algorithm, eventually achieves a great acceleration and allows to reconstruct images of the gamma radiation produced by proton beam in real time. The object of this paper is to improve the run time of SOE algorithm for improving the accuracy of the proton therapy. In previous studies, it is difficult to reconstruct images of prompt gamma (PG) ray in real time in proton therapy. After analyzing the structure of the SOE algorithm, we correspond each gamma ray detected by Compton camera (CC) to each thread in GPU, initialize the origin cones in GPU, and use data structures which are suitable for parallelization, shared memory, and random number lists to speed up parallel program. To evaluate the proposed method, we use the parallel SOE algorithm to reconstruct the sources with the CC imaging system, which is simulated by Geant4. The parallel program on the GPU eventually achieves a 25× speedup over serial CPU run, reconstructing images of gamma radiation in 0.4 s. In the end, we also accelerate the Monte Carlo-based back projection (MC-BP) algorithm, the parallel program achieves a 79× speedup over serial CPU run.

Estimation of respiratory phases during proton radiotherapy from a 4D-CT and Prompt gamma detection profiles

Proton radiotherapy has a potential to provide an effective cancer treatment while sparing greater volume of healthy tissue than the conventional X-ray based radiotherapy. However, in lungs this potential is hindered by motion due to breathing. An important quantity in treatment verification is the correlation between the respiratory phases (RP) and the timing of pencil beam scanning (PBS). In this note, we demonstrate how the RP can be estimated using Prompt gamma (PG) detection profiles collected during a treatment. We utilized a 4D-CT of a patient with lung cancer, a treatment plan and a PG simulator. The treatment plan consisted of ten layers corresponding to ten proton energies. The RPs of the 4D-CT were interpolated using a deformable registration algorithm, so as to have fifty RPs in total. Deviations from regular breathing were introduced via time dependent frequency modulation. Fifty unique breathing patterns were generated, for which PG profiles were simulated for each pencil beam. Poisson noise was added to each PG profile to account for photon statistics. The RPs were estimated by comparing the PG profiles with and without Poisson noise via three different methods: the RP associated with each layer was estimated 1) independently of the other layers, 2) using a linear correlation between the layers, and 3) using a quadratic correlation between the layers. The best model, the quadratic model, yielded an average error in RP estimation relative to the breathing period of 5% of the breathing period or less with a 90% confidence interval.

Non-Destructive Characterization of Mechanically Processed Waste Printed Circuit Boards: X-ray Fluorescence Spectroscopy and Prompt Gamma Activation Analysis

This work aimed to characterize the deportment/concentration and liberation/association of the metals and light elements within mechanically processed waste printed circuit boards (PCBs) that hold the complex and heterogeneous structure and distribution of different material components. Waste PCBs passed through a series of mechanical processing (i.e., comminution and sieving) for metal recovery and were then characterized without further destroying the particles in order to capture their heterogeneity. The characterizations were performed in a laboratory and large-scale neutron facility. The results obtained with a portable X-ray fluorescence spectroscopy and prompt gamma activation analysis were compared and confirmed the good agreement and complementarities in general. The advantages and disadvantages of the two different methods were identified and discussed in this paper, in relation to their application to the analysis of mechanically processed PCB particles.

Conceptual design of prompt gamma neutron activation analysis facility at Tehran Research Reactor for BNCT application

Abstract Since Tehran Research Reactor (TRR) is the only available neutron source , which can be used for Boron Neutron Capture Therapy (BNCT) in Iran, it is essential to provide an appropriate analysis system at TRR in order to determine 10 B concentration in sample tissue or blood. Based on the advantages, Prompt Gamma Neutron Activation Analysis (PGNAA) facility has been selected. Irradiation channels in TRR have been studied using Monte Carlo MCNPX2.6 code and evaluated to provide the appropriate neutron beam for PGNAA. Based on the results of neutron intensity and spectrum, F-beam tube is considered to be the most favorable for PGNAA, and has therefore been selected for further investigation and MCNP simulation. Bismuth blocks for decreasing gamma radiation , and Fluental™ as a filter for fast neutron have been used in F-beam tube. The convergent collimator with iron and polyethylene has been considered to shape the neutron beam and to reduce the neutron and gamma-ray fluxes at the position of the HPGe gamma-ray detector. The sensitivity of the designed system is determined, from MCNP simulation, to be 7.35 cps/ μ g.

Characterization of prompt gamma ray emission for in vivo range verification in particle therapy: A simulation study

In this paper we investigate the emission and detection characteristics of prompt gamma (PG) rays for in vivo range verification during hadron therapy, using Geant4 simulations. Proton, 4He and 12C beams of varying energy are incident on water phantoms. The PG production yield, energy spectral characteristics and spatial correlation with the Bragg Peak (BP) have been quantified. Further, the angular distributions for PG detection with respect to a point-of-reference on the phantom surface have been explored. The temporal properties of PG emission and time-of-flight (TOF) of PG detection have also been investigated in correlation with the changing particle beam range. Our results show that the primary PG rays from nuclear interactions of the primary beam exhibit the closest correlation to the beam range but its signal is significantly masked by the concurrent secondary PG rays, particularly for heavier ions such as carbon ion beams. The PG TOF spectroscopy encodes the essential information of the beam range but requires high time resolution measurements to retrieve it. A hybrid PG detection system to utilize the energy, timing and spatial characteristics of PG rays is desirable for BP tracking in real-time.

Simulation of a collimator and sapphire filter for PGAA facility of the Moroccan TRIGA MARK II research reactor

The Prompt Gamma Neutron Activation Analysis (PGAA) facility will be commissioned at the NB1 beam tube of the Moroccan TRIGA MARK II research reactor. PGAA is a non-destructive analytical technique used for multi-elemental analysis and especially for light element analysis. For better performances, PGAA requires small and focused beam, and high Фth/Фep and Фth/Фfast ratios, and low background gamma radiation. For this purpose, fast neutron filters are commonly used to reduce fast and epithermal components of neutron flux. In this paper, the impact of sapphire filter, introduced, within the collimator hole, at the beam port on neutron spectra was evaluated. Monte Carlo, MCNP6.2, code has been used with ENDF VII.1 neutron cross section library to perform this study. An approximate TRIGA MARK II reactor MCNP model has been used to generate neutron spectra at the entrance of the collimator. Then an independent model for both collimator and sapphire filter has been brought into calculation to fulfil our purpose. Results showed an increase of about 8 times for both Фth/Фep and Фth/Фfast ratios using a 10 cm length of sapphire.

Investigation of in vivo beam range verification in carbon ion therapy using the Doppler Shift Effect of prompt gamma: A Monte Carlo simulation study

Carbon ion therapy has received increasing attention because of its excellent physical dose distribution and high biological effect comparing against the conventional radiotherapy. However, the range uncertainty is still a major issue that limits further improvement of the treatment efficiency. Hence, we propose a novel method for reducing the range uncertainty in carbon ion therapy based on the Doppler Shift Effect of prompt gamma (PG), which can quantify the average carbon energy by the significant energy shift of the 4.44 MeV PG in the spectrum and then calibrate the range. Specifically, the influences of heterogeneity, initial carbon beam configuration, and detected direction are thoroughly discussed using the Monte Carlo simulation in this paper. Results show a moderate difference (<3.5%) between the Monte Carlo simulation and the analytical calculation, which verify the theoretical feasibility and veracity of the proposed method. The different initial energies (200, 225, 250, 300, and 400 MeV/u) and energy spreads (0%, 0.5%, 1%, 2%) of carbon beam have a not obvious influence on the accuracy of this method. When the detected direction changes from 90° to 50°, the PG energy shift overturns from “red shift” to “blue shift” and the difference value increases significantly. Moreover, for inhomogeneous phantoms, this method can distinguish the different ranges with blocks filled by different materials (bone, adipose, and air) in the beam path. Finally, through the analysis of range verification error with cavities of different thicknesses (0–30 mm) in the water phantom, the precision of the proposed method in theory is determined to be 0.008%–6.253%, and this value can be less than 3% with an appropriate detection site. These results indicate that the measurement of the PG energy shift could be applied to reduce the range uncertainty on the basis of the Doppler Shift Effect in carbon ion therapy.

Correlations between the shifts in prompt gamma emission profiles and the changes in daily target coverage during simulated pencil beam scanning proton therapy

The aim of this study was to investigate the feasibility of using prompt gamma (PG) ray emission profiles to monitor changes in dose to the planning target volume (PTV) during pencil beam scanning (PBS) proton therapy as a result of day-to-day variation in patient anatomy.For 11 prostate patients, we simulated treatment plan delivery using the patients’ daily anatomy as observed in the planning CT and 7–9 control CT scans, including the detected PG profiles resulting from the 5%, 10%, and 20% most intense proton pencil beams. For each patient, we determined the changes in dosimetric parameters for the high- and low-dose PTVs between the simulations performed using the planning CT scan and the different control CT scans and correlated these to changes in the PG emission profiles.Changes in coverage of the high- and low-dose PTV correlated most strongly with the median and mean absolute PG emission profile shifts of the 5% most intense pencil beams, respectively. With a mean Pearson correlation coefficient of −0.76 (SD: 0.17) for the high-dose PTV and of −0.60 (SD: 0.51) for the low-dose PTV.We showed, as a proof of principle, that PG emission profiles obtained during PBS proton therapy could be used to detect changes in PTV coverage due to day-to-day anatomical variation.

An Archaeometallurgical Investigation on Metal Samples from the Chiaravalle Cross

The production and manufacturing techniques of metals involve expertise, and the study of ancient artifacts relies on interdisciplinary skills. Metalworking processes used in the production of jewelry masterpieces can, for example, give indications on the provenance of an ancient object of an unknown origin and the techniques used. In this regard, metallic samples from the Chiaravalle Cross (a beautiful processional cross with a complex structure, dating to the 13th century) have been studied, combining bulk and point measurements. Neutron-based experiments (like Prompt Gamma Activation Analysis and neutron diffraction) provide the bulk of the elemental and mineralogical composition, while particle induced X-ray emission analyses evidenced important details on its manufacturing techniques.

Radiative-capture cross sections for the La139(n,γ) reaction using thermal neutrons and structural properties of La140

A set of prompt partial $\gamma$-ray production cross sections from thermal neutron-capture were measured for the $^{139}$La($n,\gamma$) reaction using a guided beam of subthermal (thermal and cold) neutrons incident upon a $^{\rm nat}$La$_{2}$O$_{3}$ target at the Prompt Gamma Activation Analysis facility of the Budapest Research Reactor. Absolute $^{140}$La cross sections were determined relative to the well-known comparator $^{35}$Cl($n,\gamma$) cross sections from the irradiation of a stoichiometric $^{\rm nat}$LaCl$_{3}$ sample. The total cross section for radiative thermal neutron-capture on $^{139}$La from the sum of experimentally measured cross sections observed to directly feed the $^{140}$La ground state was determined to be $\sigma_{0}^{\rm expt} = 8.58(50)$ b. To assess completeness of the decay scheme and as a consistency check, the measured cross sections for transitions feeding the ground state from levels below a critical energy of $E_{c} = 285$ keV were combined with a modeled contribution accounting for ground-state feeding from the quasicontinuum to arrive at a total cross section of $\sigma_{0} = 9.36(74)$ b. In addition, a neutron-separation energy of $S_{n} = 5161.005(21)$ keV was determined from a least-squares fit of the measured primary $\gamma$-ray energies to the low-lying levels of the $^{140}$La decay scheme. Furthermore, several nuclear structure improvements are proposed for the decay scheme. The measured cross-section and separation-energy results are comparable to earlier measurements of these quantities.

Compton-based prompt gamma imaging using ordered origin ensemble algorithm with resolution recovery in proton therapy

Prompt gamma ray (PG) imaging based on Compton camera (CC) is promising to realize in vivo verification during the proton therapy. However, the finite spatial and energy resolution of current CC, as well as the Doppler broaden effect, degrade the quality and resolution of PG images. In addition, due to the inherent geometrical complexity of Compton camera data, PG imaging can be time-consuming and difficult to reconstruct in real-time, while using standard techniques such as filtered back-projection or maximum likelihood-expectation maximization. In this paper, we propose three modifications of origin ensembles with resolution recovery (OE-RR) algorithm based on Markov chains to accelerate the convergence to equilibrium of OE-RR algorithm and improve the image quality. For evaluation, we performed a Monte Carlo simulation of a three-stage CZT Compton camera with resolution loss to detect the PG produced by a proton beam in a water phantom, and evaluate image quality of the gamma rays emitted during proton irradiation. The results show that our ordered OE-RR algorithm realized a good resolution recovery and accurate estimation of the position, including the peak and the distal falloff of the PG emission with remarkably faster reconstruction, thus demonstrating the feasibility of this new method in non-idealized PG-based proton range verification.

Determination of elemental concentrations in biological and geological samples using PGNAA facility at the Dalat research reactor

This article presents the results of the determination of element concentrations in biological and geological samples by using the Prompt Gamma Neutron Activation Analysis (PGNAA) facility that was installed at horizontal channel No. 4 of the Dalat research reactor. The biological standard sample Bovine Liver NBS 1577a and environmental standard sample Coal Fly Ash NBS 1633a were analyzed to verify the analytical ability of the facility. After that, the concentrations of N, K, Cl, Fe, Ca, Mn and B in biological samples and concentrations of K, Al, Si, Fe, Ca, Mn, Gd, Sm, Ti, and B in geological samples were determined in the framework of quality assurance and quality control programme at the Dalat Nuclear Research Institute. The analytical results indicated that this PGNAA facility can be used as a suitable instrumental tool to study in the fields of environment, biology and geology.

Application of the collective model to determine some rotational bands of 239U nucleus

238U material is component in fuels of nuclear reactor core. Understanding properties and structure of 238U nucleus is necessary before simulating and designing nuclear reactor. Besides that, the study of nuclear reaction is necessary to identify the specific characteristics of nucleus, it is the most effective experimental method up to now. However, in order to explain the properties of nuclear structure, in addition to study of the nuclear reaction, nuclear structure models and its theory must be used. There are many nuclear structure models to solve those properties of nucleus. This paper presents application of the Collective Model to determine some rotational bands of 239U nucleus, using Prompt gamma neutron activation analysis method (PGNAA). Experiment is performed at channel No.2 of Dalat Research Reactor (DRR), using Filtered Thermal Neutron Beam and Compton Suppression Spectroscopy with High – Purity Germanium detector (HPGe). The results have found 11 rotational bands of 239U nucleus. This work is very necessary for the research of nuclear structure which controls material technology by itself.

Characterization of prompt gamma rays for in-vivo range verification in hadron therapy: A Geant4 simulation study

Prompt gamma (PG) rays have been proposed for in-vivo beam range verification during treatment delivery. As a secondary by-product emitted almost instantaneously upon ion-nuclear interaction, PG rays offer real-time tracking of the Bragg peak (BP). However their detection is challenging since they have a broad energy spectrum with interference from neutrons and stray gamma rays. Numerous approaches have been proposed to utilise PG for in-vivo beam range verification. In this work, Geant4 Monte Carlo (MC) simulations have been used to study the spectral, spatial, temporal and angular distribution characteristics of PG emission and detection from hadron radiation fields of varying energy. Proton, 12C and 4He beams irradiated homogeneous water phantoms. These studies will provide valuable information for the development of clinically suitable and reliable PG detector systems.

Provenance study on prehistoric obsidian objects found in Romania (Eastern Carpathian Basin and its neighbouring regions) using Prompt Gamma Activation Analysis

Macroscopic characteristics, such as hardness, relatively easy workability, transparency, translucency, and shiny black colour of the Carpathian 1 (C1) type obsidian, which is one significant variety of the Carpathian obsidians made, it highly valuable in the Prehistoric times. It was transported several hundreds of kilometres away from the geological source, becoming wide-spread in the Eastern part of the Carpathian Basin as well.Seventy-two pieces of Prehistoric (Neolithic to Bronze Age) obsidian artefacts (tools, arrow heads, chips and fragments) found in different parts of Romania (Transylvania, Banat and Muntenia) have been investigated by non-destructive prompt-gamma activation analyses. The aim of the study was to determine the provenance of their raw materials. The geochemical composition of the artefacts showed high similarity with that of the obsidian samples collected at outcrops from the Slovakian side of the Tokaj Mountains. Based on characteristic major and trace element concentrations, most of the studied Romanian obsidian artefacts are characterized as C1 type obsidians. However, some archaeological pieces from Banat and Muntenia have been identified as Carpathian 2 (C2, Tolcsva-Erdőbénye and Mád) type. Based on the PGAA results, any other provenance, such as Lipari, Melos, Sardinia, Yali, Antiparos or Armenia can be excluded with high significance. Our results suggest that in parallel with the predominance of the C1 type obsidian raw material in the Transylvanian Basin, simultaneous use of C2 type obsidian raw material can be shown outside Transylvania (in Banat and Muntenia) and especially during the Neolithic. This can imply different connections and raw material supply routes from the Tokaj Mountains to Transylvania and to the southern regions during the Neolithic and the Copper Age.

Correction of Geometrical Effects of a Knife-Edge Slit Camera for Prompt Gamma-Based Range Verification in Proton Therapy

Prompt gamma (PG) based range verification can potentially reduce the safety margins in proton therapy. A knife-edge slit camera has been developed in this context using analytical PG simulations as reference for absolute range verification during patient treatment. Geometrical deviations between measurement and simulation could be observed and have to be corrected for in order to improve the range retrieval of the system. A geometrical correction model is derived from Monte Carlo simulations in water. The influence of different parameters is tested and the model is validated in a dedicated benchmark experiment. We found that the geometrical correction improves the agreement between measured and simulated PG profiles resulting in an improved range retrieval and higher accuracy for absolute range verification. An intrinsic offset of 1.4 mm between measurement and simulation is observed in the experimental data and corrected in the PG simulation. In summary, the absolute range verification capabilities of a PG camera have been improved by applying a geometrical correction model.

Toward a new treatment planning approach accounting for in vivo proton range verification

Protons with modern pencil-beam scanning delivery are widely used in state-of-the-art radiotherapy. To reduce the unwanted effect of proton range uncertainties, prompt gamma (PG) monitoring is investigated and considered one of the most promising methods for real-time, in vivo range verification. Despite good correlation between the penetration depth of the PG signal and proton range in most cases, mismatch can occur especially because of tissue heterogeneities. Moreover, detectability and reproducibility of the prompt gamma signal critically depends on counting statistics. Nowadays, conventional treatment planning systems do not account for the degree of correlation between dose and PG signal nor the expected PG signal counting statistics, which considerably influences the possibility of a reliable verification of the intended beam range. Hence, in this project, we investigate a new treatment planning approach, in which the spot-by-spot conformities between PG and dose profiles (PG-dose correlation) as well as PG signal detectability and precision are taken into account based on a TPS optimizer. To investigate the feasibility of this idea, a research computational platform, combining Monte Carlo (MC, Geant4) pre-calculated pencil beams with the analytical Matlab-based TPS engine CERR, is used for treatment planning. Geant4 is employed for realistic simulation of the dose delivery and PG generation of all spots in the heterogeneous patient anatomy given by CT images. First of all, a treatment plan is created using a charged particle extension of CERR. Secondly, the PG fall-off positions of all individual pencil beams are evaluated and compared to the 80% distal dose fall-off positions. Thirdly, the PG-dose correlations of all spots are quantified. A new plan, in which a few spots with the best PG-dose correlation are boosted to ensure PG detectability with good precision, is then made. Finally, the optimized plan is fully recalculated on the same patient CT using Geant4, and the result is evaluated considering both plan quality and beam range monitorability. The evaluation shows that the re-optimized treatment plan is comparable to the initial plan in terms of dose distribution, dose averaged LET distribution and robustness, while fulfilling the set statistical conditions for reliable PG monitoring of the few automatically or manually selected spots. The method could thus complement, and for the selected pencil beams even overcome limitations of, alternative suggested approach such as pencil beam aggregation to provide sufficient counting statistics for precise PG range retrieval with good correlation to the treatment dose.

Accuracy of using high-energy prompt gamma to verify proton beam range with a Compton camera: A Monte Carlo simulation study

Prompt gamma (PG) rays emitted during proton therapy has been used for proton range verification. Because high-energy PG emission is well correlated to the Bragg peak (BP), high-energy PG rays are well-suited for proton range verification. However, the low production and detection of high-energy PG rays often lead to inaccurate BP position estimates. The aim of this study is to improve the BP position estimates obtained from high-energy PG rays. We propose a BP position estimation method based on the local maximum closest to the distal fall-off region. We present the results of Monte Carlo simulations in which a water phantom was irradiated with a proton beam. Our results show that the BP position estimated from the 6.13 MeV PG rays can be improved using the proposed position estimation method. Moreover, the 6.92 and 7.12 MeV PG rays can be used for predicting the BP position. However, the accuracy of the BP position estimation decreases with decreasing tissue oxygen levels. We also found that the subtraction of the PG images of 6.13 MeV from those of 6.92 and 7.12 MeV can be used to predict the BP position with a mean accuracy of < 2 mm. The accurate estimation of the BP position can be achieved using different high-energy PG rays, but factors including position estimation, irradiated tissue and event selection should be carefully taken into account.