Monte Carlo Program Research Articles

A Monte Carlo study on the performance evaluation of a parallel hole collimator for a HiReSPECT: A dedicated small-animal SPECT

Collimator geometry has an important contribution on the image quality in SPECT imaging. The purpose of this study was to investigate the effect of parallel hole collimator hole-size on the functional parameters (including the spatial resolution and sensitivity) and the image quality of a HiReSPECT imaging system using SIMIND Monte Carlo program. To find a proper trade-off between the sensitivity and spatial resolution, the collimator with hole diameter ranges of 0.3–1.5 mm (in steps of 0.3 mm) were used with a fixed septal and hole thickness values (0.2 mm and 34 mm, respectively). Lead, Gold, and Tungsten as the LEHR collimator material were also investigated. The results on a 99mTc point source scanning with the experimental and also simulated systems were matched to validate the simulated imaging system. The results on the simulation showed that decreasing the collimator hole size, especially in the Gold collimator, improved the spatial resolution to 18% and 3.2% compared to the Lead and the Tungsten, respectively. Meanwhile, the Lead collimator provided a good sensitivity in about of 7% and 8% better than that of Tungsten and Gold, respectively. Overall, the spatial resolution and sensitivity showed small differences among the three types of collimator materials assayed within the defined energy. By increasing the hole size, the Gold collimator produced lower scatter and penetration fractions than Tungsten and Lead collimator. The minimum detectable size of hot rods in micro-Jaszczak phantom on the iterative maximum-likelihood expectation maximization (MLEM) reconstructed images, were determined in the sectors of 1.6, 1.8, 2.0, 2.4 and 2.6 mm for scanning with the collimators in hole sizes of 0.3, 0.6, 0.9, 1.2 and 1.5 mm at a 5 cm distance from the phantom. The Gold collimator with hole size of 0.3 mm provided a better image quality with the HiReSPECT imaging.

Recursive model for the fragmentation of polarized quarks

We present a model for Monte Carlo simulation of the fragmentation of a polarized quark. The model is based on string dynamics and the ${}^3P_0$ mechanism of quark pair creation at string breaking. The fragmentation is treated as a recursive process, where the splitting function of the subprocess $q \to h + q'$ depends on the spin density matrix of the quark $q$. The ${}^3P_0$ mechanism is parametrized by a complex mass parameter $\mu$, the imaginary part of which is responsible for single spin asymmetries. The model has been implemented in a Monte Carlo program to simulate jets made of pseudoscalar mesons. Results for single hadron and hadron pair transverse-spin asymmetries are found to be in agreement with experimental data from SIDIS and $e^+e^-$ annihilation. The model predictions on the jet-handedness are also discussed.

Accelerating lattice QCD simulations with 2 flavors of staggered fermions on multiple GPUs using OpenACC—A first attempt

We present the results of an effort to accelerate a Rational Hybrid Monte Carlo (RHMC) program for lattice quantum chromodynamics (QCD) simulation for 2 flavors of staggered fermions on multiple Kepler K20X GPUs distributed on different nodes of a Cray XC30. We do not use CUDA but adopt a higher level directive based programming approach using the OpenACC platform. The lattice QCD algorithm is known to be bandwidth bound; our timing results illustrate this clearly, and we discuss how this limits the parallelization gains. We achieve more than a factor three speed-up compared to the CPU only MPI program.

Preliminary study on protection of synchrotron radiation damage in CEPC main ring

The Circular Election–Positron Collider has been proposed by Institute of High Energy Physics (IHEP, CAS). The beam in the main ring with energy up to 120 GeV would produce intense synchrotron radiation (SR) with photon energy up to several MeV. Without shielding, this radiation would be harmful to the accelerator components. To clarify the radiation damage, analyze the source of SR, and design the shielding system to protect the accelerator. The theoretical formula has been used to estimate the spectrum and distribution of SR. Several ways of designing or shielding vacuum chamber with different geometries and various materials are put forward to protect sensitive facility components. The Monte Carlo program FLUKA has been introduced to calculate cumulative dose and heat deposition in all designing cases. The SR in CEPC main ring would be harmful to the coil used in dipole magnets. The design based on LEP with aluminum and lead would need 23 mm lead to make the coil safe. The design based on LEP with copper would need 28 mm of outer copper. And the copper chamber and lead shield design would need 16 mm of Lead. The theoretical formula has been used in source generation of Monte Carlo program to get the distribution of SR in CEPC main ring. The program was also used to simulate SR problems in the vacuum chamber with designs of different geometries and materials. Among these designs, the elliptical pipe with lead shield is preferred in CEPC.

An update on the BQCD Hybrid Monte Carlo program

We present an update of BQCD, our Hybrid Monte Carlo program for simulating lattice QCD. BQCD is one of the main production codes of the QCDSF collaboration and is used by CSSM and in some Japanese finite temperature and finite density projects. Since the first publication of the code at Lattice 2010 the program has been extended in various ways. New features of the code include: dynamical QED, action modification in order to compute matrix elements by using Feynman-Hellman theory, more trace measurements (like Tr(D-n) for K, cSW and chemical potential reweighting), a more flexible integration scheme, polynomial filtering, term-splitting for RHMC, and a portable implementation of performance critical parts employing SIMD.

MCDoseE 2.0 A new Markov Chain Monte Carlo program for ESR dose response curve fitting and dose evaluation

Abstract This study presents MCDoseE 2.0, a new fitting program for ESR dating dose response curve (DRC) fitting and dose calculation. The standalone software was specifically designed to remove assumed data weighting, and instead to obtain a full probabilistic solution of the DRC by propagating the uncertainties associated with the measured ESR intensities. It uses a non-linear Bayesian framework, specifically a Markov Chain Monte Carlo (MCMC) scheme based on the Metropolis-Hastings algorithm, where the solution is a probability distribution for the equivalent dose, according to the precision of the measurements. In this paper, we investigate the capabilities and limitations of MCDoseE 2.0 by comparing our results to those obtained with OriginPro 9.1 ® , a proven and commonly used commercial software package. The two programs were evaluated against both known-dose samples and random archaeological tooth enamel and quartz samples, using three commonly used DRC fitting functions. We found that both programs provide highly consistent results. When comparing the dose estimates obtained by both programs we found that 90% of the solutions are statistically indistinguishable regardless of the data weighting assumption used in OriginPro. We also found that MCDoseE 2.0 offers an increased precision on the ending results compared to the commercial software, as long as each measured ESR uncertainty remains within 2-sigma range of the mean error value of all measured ESR uncertainties of the dataset. The accuracy of the fitting results given by MCDoseE 2.0 are undeniably dependent on the measurement accuracy, and emphasises the need of a proper assessment of the experimental errors in the ESR intensities. A copy of the program is available in Supplementary information, and some basic instructions for its use are provided, as well as recommendations to ensure reliable and accurate fitting results.

24. Monte Carlo program for radioprotection of patients and medical staff in interventional radiology

Introduction Interventional radiology is a medical procedure presenting a risk of significant exposure to ionizing radiations for the patient, but also for the medical staff close to the operating table. Nowadays Monte Carlo simulation is one of the most accurate means for estimating dosimetric quantities, but the important computation time remains one of the main limitations to its clinical use. In this context, a Monte Carlo program is being developed to allow a rapid and automated post-operative calculation of a patient’s dosimetric quantities (dose to the organs, skin dose maps) and a real-time visualization of the 3D dose field in the operating room. Methods The proposed program uses the Monte Carlo GATE simulation code, a reference in the field of dosimetry [1] , combined with advanced variance reduction methods (TLE, seTLE [2] ). Post-operative patient dosimetry calculations use the parameters provided by the machine (DICOM images), as well as experimental measurements with a device specifically developed for this application. Regarding the radioprotection of the medical staff, the real-time visualization of the dose field in the operating room is based on the prior creation of a database specific to the installation. Results The comparison of the first Monte Carlo results, with on-site ionization chamber measurements, showed a difference of less than 5% for the reconstruction of kerma in air in the primary beam and less than 10% for that of the scattered beam at one meter from the operating table. The use of variance reduction methods allows a post-operative calculation of the patient dose to be made in less than 15 min with a statistical uncertainty less than 5%. Conclusions By combining a reduced execution time and a precise modelization of interventions, the developed program makes these Monte Carlo calculations compatible with clinical routine use. It provides a realistic estimation of the dose delivered to the patient in case of overexposure and allows the medical staff an immediate assessment of the risk associated with the exposure to ionizing radiations during surgery.

Monte Carlo-based quantitative pinhole SPECT reconstruction using a ray-tracing back-projector

BackgroundMonte Carlo simulations provide accurate models of nuclear medicine imaging systems as they can properly account for the full physics of photon transport. The accuracy of the model included in the maximum-likelihood–expectation-maximization (ML-EM) reconstruction limits the overall accuracy of the reconstruction results. In this paper, we present a Monte Carlo-based ML-EM reconstruction method for pinhole single-photon emission computed tomography (SPECT) that has been incorporated into the SIMIND Monte Carlo program. The Monte Carlo-based model, which accounts for all of the physical and geometrical characteristics of the camera system, is used in the forward-projection step of the reconstruction, while a simpler model based on ray-tracing is used for back-projection. The aim of this work was to investigate the quantitative accuracy of this combination of forward- and back-projectors in the clinical pinhole camera GE Discovery NM 530c.ResultsThe total activity was estimated in 99mTc-filled spheres with volumes between 0.5 and 16 mL. The total sphere activity was generally overestimated but remained within 10% of the reference activity defined by the phantom preparation. The recovered activity converged towards the reference activity as the number of iterations increased. Furthermore, the recovery of the activity concentrations within the physical boundaries of the spheres increased with increasing sphere volume. Additionally, the Monte Carlo-based reconstruction enabled recovery of the true activity concentration in the myocardium of a cardiac phantom mounted in a torso phantom regardless of whether the torso was empty or water-filled. A qualitative comparison to data reconstructed using the clinical reconstruction algorithm showed that the two methods performed similarly, although the images reconstructed using the clinical software were more uniform due to the incorporation of noise regularization and post-filtration in that reconstruction technique.ConclusionsWe developed a Monte Carlo-based reconstruction method for pinhole SPECT and evaluated it using phantom measurements. The combination of a Monte Carlo-based forward-projector and a simplified analytical ray-tracing back-projector produced quantitative images of acceptable image quality. No explicit calibration is necessary in this method since the forward-projector model maintains a relationship between the number of counts and activity.

The Backscattering Phase Function for a Sphere with a Two-Scale Relief of Rough Surface

The backscattering of light from spherical surfaces characterized by one and two-scale roughness reliefs has been investigated. The analysis is performed using the three-dimensional Monte-Carlo program POKS-RG (geometrical-optics approximation), which makes it possible to take into account the roughness of objects under study by introducing local geometries of different levels. The geometric module of the program is aimed at describing objects by equations of second-order surfaces. One-scale roughness is set as an ensemble of geometric figures (convex or concave halves of ellipsoids or cones). The two-scale roughness is modeled by convex halves of ellipsoids, with surface containing ellipsoidal pores. It is shown that a spherical surface with one-scale convex inhomogeneities has a flatter backscattering phase function than a surface with concave inhomogeneities (pores). For a sphere with two-scale roughness, the dependence of the backscattering intensity is found to be determined mostly by the lower-level inhomogeneities. The influence of roughness on the dependence of the backscattering from different spatial regions of spherical surface is analyzed.

Model of Intraperitoneal Targeted α-Particle Therapy Shows That Posttherapy Cold-Antibody Boost Enhances Microtumor Radiation Dose and Treatable Tumor Sizes.

Intraperitoneally administered radiolabeled monoclonal antibodies (mAbs) have been tested in several clinical trials, often with promising results, but have never proven curative. Methods: We have previously presented simulations of clinically relevant amounts of intraperitoneal 90Y-mAbs for treatment of minimal disease and shown that such treatments are unlikely to eradicate microtumors. Our previous model simulated the kinetics of intraperitoneally infused radiolabeled mAbs in humans and showed the benefit of instead using α-emitters such as 211At. In the current work, we introduce penetration of mAbs into microtumors with radii of up to 400 μm. Calculations were performed using dynamic simulation software. To determine the radiation dose distribution in nonvascularized microtumors of various sizes after intraperitoneal 211At-radioimmunotherapy, we used an in-house-developed Monte Carlo program for microdosimetry. Our aim was to find methods that optimize the therapy for as wide a tumor size range as possible. Results: Our results show that high-specific-activity radiolabeled mAbs that are bound to a tumor surface will penetrate slowly compared with the half-lives of 211At and shorter-lived radionuclides. The inner-core cells of tumors with radii exceeding 100 μm may therefore not be sufficiently irradiated. For lower specific activities, the penetration rate and dose distribution will be more favorable for such tumors, but the dose to smaller microtumors and single cells will be low. Conclusion: Our calculations show that the addition of a boost with unlabeled mAb 1-5 h after therapy results in sufficient absorbed doses both to single cells and throughout microtumors up to approximately 300 μm in radius. This finding should also hold for other high-affinity mAbs and short-lived α-emitters.

Toward high-efficiency and detailed Monte Carlo simulation study of the granular flow spallation target

The dense granular flow spallation target is a new target concept chosen for the Accelerator-Driven Subcritical (ADS) project in China. For the R&D of this kind of target concept, a dedicated Monte Carlo (MC) program named GMT was developed to perform the simulation study of the beam-target interaction. Owing to the complexities of the target geometry, the computational cost of the MC simulation of particle tracks is highly expensive. Thus, improvement of computational efficiency will be essential for the detailed MC simulation studies of the dense granular target. Here we present the special design of the GMT program and its high efficiency performance. In addition, the speedup potential of the GPU-accelerated spallation models is discussed.

Research on optical simulation system for halftone printing dot with Monte Carlo method

The optical simulation system of printing dot is proposed, which could promote optical study of printing dots properties and improve printing quality. The optical simulation system was built based on Monte Carlo program that can simulate photons propagation path in paper. Once inputting the optical parameters of paper and ink, the optical dot simulation program will simulate millions of photons propagation path in prints. After analyzing statistical information of photons, dot morphology and dot reflective data can be obtained. The results showed that simulation system is versatile and easy to operate, besides the simulated dot shape and reflectance quite approached to realistic printing condition. The optical simulation system could sufficiently accomplish printing dot optical properties simulation, which provides a new way to predict and control printing quality.

Abstract ID: 232 The dawn of PET Monte Carlo: A personal experience

In the seventies, several Monte Carlo programs were available in radiation physics. I had already developed a home-made Monte Carlo code for neutron transport to validate the experimental measurements of the efficiency of a large neutron counter for 10–200 MeV neutrons in a HEP experiment, when I participated at the first international on “Computer techniques in radiation transport and dosimetry”, organized by Walter R. Nelson and Theodore Jenkins in Erice (Trapani, Italy) in 1978: Graham Stevenson, Keran O’Brien, W. W. Engle, T. A. Gabriel, C. Ponti, Walter R. Nelson, Herbert Dinter, A. Van Ginneken, Tony W. Armstrong and J. Ranft were the speakers. It was there that I met with the EGS code and its author Walter Ralph Nelson. Since then I started my collaboration with Ralph Nelson on the use of the EGS3 Monte Carlo in Nuclear Medicine, with the first paper published in 1980 on Compton Tomography, followed by a series of papers on the simulation of the performance of a human PET based on MWPC’s, the first one in 1981. From these first wails in the PET domain EGS3 became EGS4 and then evolved into GEANT and finally into GATE to become an indispensable code for PET detector simulation. In this talk I will present my pristine research in the field of PET Monte Carlo simulations in the last 20 years of last century.

Bi-level spatial subdivision based monte carlo ray tracing directly using CAD models

To achieve fast Monte Carlo ray tracing on CAD models, a Bi-level Spatial Subdivision based ray tracing method (BSS) is proposed in this paper. This method was implemented and integrated in Super Monte Carlo Program for Nuclear and Radiation Simulation (SuperMC) and tested on ITER Benchmark and Force-Free Helical Reactor (FFHR) model. The testing results on ITER Benchmark model demonstrate the correctness of this method. The testing results on FFHR demonstrate that this method can save most of the preprocessing work to greatly improve the Monte Carlo analysis efficiency. Both results reveal that this method achieves applicable calculation speed comparing to the traditional Constructive Solid Geometry (CSG) broadly used in Monte Carlo codes.

Measurements of muon multiple scattering in MICE

Neutrino factories have been identified as the best facility for making precision measurements of neutrino oscillation physics. To fully realize this technology, a demonstration of the reduction of the phase space of a muon beam must be presented. The Muon Ionization Cooling Experiment (MICE) is tasked with providing such a demonstration. Ionization cooling uses the energy loss in a low Z material followed by acceleration in RF cavities to reduce the phase space of a beam on a time scale many times less than the time scale of muon decay. Multiple coulomb scattering (MCS) simultaneously inflates the muon beam and so the interplay between energy loss and MCS must be well understood. Unfortunately MCS is not well simulated in the materials of interest in the GEANT Monte Carlo program. A programme has commenced for MICE to measure MCS in several materials of interest including lithium hydride, liquid hydrogen, and gaseous xenon. The experimental methods and early results will be presented.

Simulation of Gamma Rays Attenuation Through Matters Using the Monte Carlo Program

This research focuses on simulation of the radiation attenuation using a Monte Carlo program called GEANT4. In the simulation, properties and geometries of the shielding system including thickness and element of the shielding material can be varied. The radiation in gamma rays regime is considered to be emitted from a Cs-137 radioactive source. The number of gamma photons at specific energy of 661.7 keV is calculated to compare the ability of radiation attenuation for different shielding materials with variable thickness. In addition, the experimental investigation was performed for three materials, which are lead, aluminum and iron, by using a NaI(Tl) scintillation detector. Then, the XCOM database were calculated to compare the results with the simulation. Both XCOM and simulation data as well as the experimental results are agreed well to the theoretical suggestion. Consequently, the results from Monte Carlo simulation with program GEANT4 can be used to design the radiation shielding system for radioactive laboratories, particle accelerator institutes, radiotherapy area in hospitals, nuclear power plants, etc.

Advanced geometry navigation methods without cavity representation for fusion reactors

Particle transport simulations of models comprising large numbers of complex and irregular geometrical shapes is a great challenge in neutronics design and analysis of fusion reactors. All the space in the particle transport universe should be described including cavity in MCNP which is the most common deployed tool in fusion reactors. The quality of the cavity directly affects the calculation accuracy and efficiency. In view of the difficulty in describing the cavity and the instability of calculation efficiency, a new geometry representation method without cavity description was formed in Super Monte Carlo Program for Nuclear and Radiation Simulation (SuperMC). Advanced geometry navigation was developed in SuperMC to get high performance for particle transport in fusion reactors. The ITER benchmark model, a validation model released by ITER International Organization, was used to verify the accuracy and efficiency of geometry representation and navigation methods in SuperMC. The results in SuperMC showed consistency with MCNP. Besides, the computation speed was 10% faster than MCNP, while it brought more convenience without cavity representation for fusion reactors.

Neutronics performance and activation calculation of dense tungsten granular target for China-ADS

Abstract Spallation target, which constitutes the physical and functional interface between the high power accelerator and the subcritical core, is one of the most important components in Accelerator Driven Subcritical System (ADS). In this paper, we investigated the neutronics performance, the radiation damage and the activation of dense tungsten granular flow spallation target by using the Monte Carlo programs GMT and FLUKA at the proton energy of 250 MeV with a beam current of 10 mA . First, the leaking neutron yield, leaking neutron energy spectrum and laterally leaking neutron distribution at several time nodes and with different target parameters are explored. After that, the displacement per atom (DPA) and the helium/hydrogen production for tungsten grains and structural materials with stainless steel 316L are estimated. Finally, the radioactivity, residual dose rate and afterheat of granular target are presented. Results indicate that granule diameter below 1 cm and the beam profile diameter have negligible impact on neutronics performance, while the target diameter and volume fraction of grain have notable influence. The maximum DPA for target vessel (beam tube) is about 1.0 (1.6) DPA/year in bare target, and increased to 2.6 (2.8) DPA/year in fission environment. Average DPA for tungsten grains is relatively low. The decline rate of radioactivity and afterheat with cooling time grows with the decrease of the irradiation time.

Planning a decentralised and bi‐directional market‐based management system

The increases in renewable current sources, prosumers and decentralised control generation in centralised grids have increased the fluctuations in electricity costs, increased the bi-direction power flow problems and changed the operation and investment of the centralised grid. These new constraints have to be observed to manage the design of the market, the new management near the load and the new operators for the power system. This study proposes a stochastic framework for the centralised grid with a market-based, decentralised management and bi-directional power flow of mixed generators of electrical energy. A decentralised and bi-directional market-based management system (DBMBMS) model is developed which considers the operation costs, security and reliability of the centralised grid, the spot market price, weather changes and the fluctuations in the load. A differential evolution technique with a Monte Carlo program is used in aggregation with bi-directional power flows to find the optimal solutions, depending on the uncertainties of the centralised grid. Using a DBMBMS model, optimal load and price management are then realised, based on the decision-maker's choices. The impacts of this new management system on the reduction of the total electricity prices of the different power sources are analysed and illustrated with practical case studies.

Evaluation of detector efficiency through GUPIXWIN H value

Abstract In this work we explore the capabilities of the GUPIXWIN software to introduce a simple and straightforward way to obtain the efficiency of X-ray detectors commonly used in PIXE (Particle-Induced X-ray Emission) experiments. To that end, all geometrical parameters of the experimental setup including details of the detector used to detect X-rays must be well known in order to calculate the solid angle subtended by the detector’s crystal. The solid angle is calculated through a Monte Carlo program developed by Taylor and co-workers which is included in the GUPIXWIN software package. The H values are obtained from a set of experiments using standards. The results for the intrinsic efficiency of a Si(Li) detector are in good agreement with those obtained from Monte Carlo calculations and are compatible with a simple exponential law.