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By means of Monte Carlo simulations of gallium nitride (GaN) planar Gunn diodes, the epilayer structure on which they are fabricated is optimized in order to achieve ultrahigh-frequency oscillations. Practical considerations, such as the limitations of the technological fabrication process and the mitigation of the huge self-heating effects expected to appear in the devices, have been also contemplated for the choice of the optimal epilayer parameters. The best results are obtained for an active layer thickness of 150 nm with doping of 5 $\times 10^{{18}}$ cm−3, which would provide 350 GHz Gunn oscillations when using a contact separation of $0.5~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

This article addresses the leader-following exponential consensus control problem for generalized one-sided Lipschitz (OSL) multiagents (MAs) using relative-state information under a directed spanning tree. Previous works have accomplished the consensus protocol design for the globally OSL nonlinear MA systems. Unlike the existing results, the proposed strategy employs a less conservative approach in the form of matrix inequalities and convex routines by assuming that the nonlinear MAs satisfy the OSL condition in a local region by relaxing the so-called quadratic inner-boundedness constraint. A novel algorithm is provided to incorporate the value of generalized OSL constant and to consider the regional consensus protocol computation via Monte Carlo simulations, based on uniform random numbers. The proposed approach is fully automatic, easily solvable, and presented for the consensus control of generalized (locally) OSL nonlinear systems for the first time. The proposed approach also studies the criteria for the exponential consensus convergence rate for attaining a faster convergence of the consensus error. Furthermore, the developed consensus protocol for the generalized OSL systems is then extended for the case of switching topologies. The proposed consensus protocol of locally OSL nonlinear MA systems can also be employed to the global OSL nonlinear MA systems as a special case for attaining the local performance. The effectiveness of the proposed approach is verified by the leader-following consensus of eight moving agents and a practical application of F-18 aircraft. [ABSTRACT FROM AUTHOR]

This work analyzes impacts on distribution networks produced by the connection of diverse types of Plug-in Electric Vehicles (PEVs), into a probabilistic framework. Some of the uncertainty sources are related with technical parameters of PEVs. Therefore, a review of PEVs currently available in the market is reported. Other uncertain parameters are related with the behavior of the PEV owners, for instance, the arrival and departure times to home, and the state of charge of the PEV when it is plugged to the grid. These parameters are modeled by using probability density functions, to then generate random numbers and perform Monte Carlo simulations. Each Monte Carlo simulation corresponds to the calculation of a power-flow in the analyzed network. The proposed methodology is tested on the IEEE 33-bus test distribution network, with the purpose of quantifying the influence of diversity of PEVs. The analysis is performed, specifically, for identify those transformers and lines that could be overloaded. Two scenarios of PEV penetration by 2025 and 2030 were assessed, i.e., considering that 10 and 30 percent of the residential customers will have at least one PEV, respectively. Obtained results reveal the importance of considering diversity of PEV model to conduct in a suitable manner this type of studies. The proposed methodology is expected to be useful for network planning expansion and to support the design of time of use tariffs. [ABSTRACT FROM AUTHOR]

CNES and ONERA have developed a radiation monitor Influence sur les Composants Avancés des Radiations de l’Espace-Nouvelle Génération (ICARE-NG) to measure the protons and electrons in radiation belts. This instrument is able to measure a wide range of energy for protons and electrons, but no measurements of few MeV protons are performed. The objective of this article is to extend the capabilities of this radiation monitor by adding a low-energy proton sensor. In this article, the design of a sensor for low-energy protons compatible with the ICARE-NG instrument is presented. Response functions for protons and electrons of the low-energy proton sensor are calculated using Monte Carlo simulations. The calculation of predicted count rates of particles is performed. The manufacturing of the instrument as well as tests is discussed. [ABSTRACT FROM AUTHOR]

While the concept of microgrids and renewable energy systems is not entirely new, these integrated technologies have become a special topic of interest for researchers, utility providers and governments. Many challenges must be overcome to achieve better integration of renewable sources into the energy framework. This study presents some viable possibilities for the utilisation of a hybridised microgrid system. The hybridisation is achieved by an efficient design approach for the enhancement of both load and system reliability indices through the intelligent placement and sizing of hybrid distributed generation (DG) systems. Real‐time models of solar photovoltaics, wind turbines, batteries and thermal DGs are presented and implemented. Also, network component failures are stochastically modelled via Monte Carlo simulations, and a general tie‐set algorithm using an adapted breadth‐first search is proposed. Moreover, mixed‐integer multi‐objective particle swarm optimisation is employed, giving a four‐dimensional Pareto solution that is attained by optimising four reliability‐related objectives, namely system average interruption frequency index, System Average Interruption Duration Index (SAIDI), Energy Not Supplied (ENS) and total cost. [ABSTRACT FROM AUTHOR]

This Letter investigates the impacts of hardware impairments (HIs) and channel estimation errors (CEEs) on the performance of non‐orthogonal multiple access (NOMA)‐based satellite communication networks. Especially, the authors obtain the closed‐form expression of the outage probability (OP) of the considered NOMA‐based satellite communication networks. Furthermore, in order to analyse the effects of HIs and CEEs in high signal‐to‐noise ratios (SNRs) regime, they derive the asymptotic expression of OP at high SNRs, which provide efficient and fast ways to evaluate the impact of system parameters on the system performance. In addition, Monte Carlo simulations are provided to verify the correctness of the analytical results. [ABSTRACT FROM AUTHOR]

In this study, free space optical communication has been studied for different atmospheric conditions. Spatial modulation (SM) has been used to improve the performance of two‐way relay cooperative communication. The proposed system employs decode and forward (DF) relaying technique along with physical layer network coding, hence it has been named as optical SM based DF two‐way relay. It enables full‐duplex communication thereby enhancing the system efficiency. The transmit optical source index as well as the information are exchanged between the two bidirectional nodes. Performance analysis of the system has been carried out in terms of lower and upper bounds of outage probability and average data rate for N‐γ cascaded fading channels. The analytical results have been validated by means of Monte Carlo simulations. The variation of the performance due to change in different parameters has also been reported in this study. [ABSTRACT FROM AUTHOR]

In this study, the authors address the problem of passive mixed near‐field and far‐field sources localisation using a uniform linear array (ULA) in which the signals received by the array may come from mixed sources. This study presents a new two stage cumulant‐based multiple signal classification (MUSIC) algorithm for passive source localisation using fourth‐order cumulants of a ULA data. The significant characteristic of the proposed algorithm is that it constructs a new special cumulant matrix to acquire more information of signals received by a ULA. Consequently, the proposed algorithm gives high direction of arrival (DOA) and range estimation accuracy, and alleviates the array aperture loss. Monte Carlo simulations are established to verify the effectiveness of the proposed method in increasing direction of arrival and range estimation accuracies. [ABSTRACT FROM AUTHOR]

This study proposes a data‐driven distributionally robust framework for unit commitment based on Wasserstein metric considering the wind power generation forecasting errors. The objective of the constructed model is to minimise the expected operating cost, including the generating cost, start‐up and shut‐down costs, and also the reserve cost, which overcomes the shortcomings of the conventional model without optimising the reserve capacity. What is more important, different from the conventional robust optimisation methods, wind power big data is fully utilised in this model to construct the ambiguity set without any presumption about its probability distribution. This is realised by Wasserstein ball with an empirical distribution as the centre. Thus, the proposed robust model is actually data‐driven and can immunise the solutions against the worst‐case distribution in the ambiguity set. In addition, the scale of the historical data is very critical for this method, the larger the scale is, the smaller the ambiguity set is and the less conservative the result is. Numerical results and Monte Carlo simulations on a real 75‐bus system demonstrate the superiority of the proposed model. [ABSTRACT FROM AUTHOR]

In this Letter, the authors propose a low-complexity estimator for the correlation coefficient based on the signed $\operatorname {\rm AR}\lpar 1\rpar $AR⁡(1) process. The introduced approximation is suitable for implementation in low-power hardware architectures. Monte Carlo simulations reveal that the proposed estimator performs comparably to the competing methods in the literature with maximum error in order of $10^{-2}$10−2. However, the hardware implementation of the introduced method presents considerable advantages in several relevant metrics, offering more than 95% reduction in dynamic power and doubling the maximum operating frequency when compared to the reference method. [ABSTRACT FROM AUTHOR]

Continuation power flow (CPF) analysis has been used in the literature to determine the voltage collapse point from active power versus voltage curves (PV curves) for steady‐state voltage stability assessment. Affine arithmetic‐based (AA) CPF analysis to determine PV curve bounds under uncertainty in power generation was introduced in the literature to overcome the problem of large computational time with Monte Carlo (MC) simulations, by getting a faster solution with a reasonably good accuracy. However, AA operations lead to more noise terms and hence overestimation of bounds. In the present work, a modified AA (modAA)‐based CPF analysis is proposed to determine PV curve bounds by considering uncertainties associated with active and reactive power injections at all buses in the system. The proposed method reduces the overestimation caused by the AA operations and gives more accurate solution bounds. The proposed modAA‐based CPF analysis is tested on 5‐bus test case, IEEE 57, European 1354 and Polish 2383‐bus systems. The simulation results with the proposed method are compared with MC simulations and AA‐based CPF analysis to show the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

In some applications, the signals received by an array are a mixture of signals emitted by both far‐field and near‐field sources. This study develops a new cumulant‐based multiple signal classification (MUSIC) algorithm for source localisation using a new structural sparse array for scenarios where both far‐field and near‐field sources coexist. The key feature of this algorithm is that it utilises fourth‐order cumulants to compute the virtual covariance matrix and constructs a new special cumulant matrix to acquire the largest number of virtual sensors and the largest array aperture for a given number of sensors. The authors provide a geometric proof to justify the utilisation of the proposed sparse linear array and compute the effective aperture of the array. The proposed algorithm increases resolution ability, direction of arrival (DOA) and range estimation accuracy, and the number of sources to be localised. Moreover, the new method has the main advantage that it does not use the information of all sensors; so that it provides somewhat low computational complexity while it uses many actual and virtual sensors. Monte Carlo simulations are provided to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Accurate understanding of surgical tool-tip tracking error is important for decision making in image-guided surgery. In this Letter, the authors present a novel method to estimate/model surgical tool-tip tracking error in which they take pivot calibration uncertainty into consideration. First, a new type of error that is referred to as total target registration error (TTRE) is formally defined in a single-rigid registration. Target localisation error (TLE) in two spaces to be registered is considered in proposed TTRE formulation. With first-order approximation in fiducial localisation error (FLE) or TLE magnitude, TTRE statistics (mean, covariance matrix and root-mean-square (RMS)) are then derived. Second, surgical tool-tip tracking error in optical tracking system (OTS) frame is formulated using TTRE when pivot calibration uncertainty is considered. Finally, TTRE statistics of tool-tip in OTS frame are then propagated relative to a coordinate reference frame (CRF) rigid-body. Monte Carlo simulations are conducted to validate the proposed error model. The percentage passing statistical tests that there is no difference between simulated and theoretical mean and covariance matrix of tool-tip tracking error in CRF space is more than 90% in all test cases. The RMS percentage difference between simulated and theoretical tool-tip tracking error in CRF space is within 5% in all test cases.

In this study, the authors propose the seismic trace noise reduction by wavelets and double threshold estimation method (STNRW), that is based on the discrete wavelet transform, estimates two thresholds instead of the one threshold estimation of the traditional methods. The authors verify the robustness of the method proving that the probability of classification error for a noisy wavelet coefficient decreases, as the length of the signal increases. The authors perform Monte Carlo simulations considering eight seismic traces obtained from astsa R package with different signal‐noise‐to‐ratio (SNR) values in order to compare the performance of the new method with three denoising methods well‐known in the literature. The results show that the STNRW method is efficient. [ABSTRACT FROM AUTHOR]

Electromechanical modes estimated from ambient wide area measurement systems measurements are often used as a basis for system dynamic security assessment. It is therefore important to know the accuracy of the mode estimates. There are two interesting phenomena widely reported in ambient mode estimation: (i) the accuracy of the mode parameter estimates improves under the lighter damping conditions and (ii) the frequency estimates are more accurate than the damping ratio estimates. This study aims to systematically investigate the estimation accuracy of ambient mode analysis. An analytical differentiation‐based perturbation method is presented to examine the variance propagation along the mode estimation procedure. Monte Carlo simulations in the two‐area system are carried out to analyse the influences of varying the mode parameters on the estimation accuracy of the inter‐area mode, in which the estimated variances are served as quantitative measures of the accuracy analysis. In addition, theoretical explanations for the observations in ambient mode estimation are also provided as a supplementary. The investigations and discussion of the estimation accuracy are of value for yielding insight into the variability of the mode estimates under ambient conditions. [ABSTRACT FROM AUTHOR]

A comprehensive approach is developed for the simulation of Single Particle Displacement Damage in silicon, from the incident particle interaction in silicon, to the resulting electrical effect observed experimentally. The different steps of the global approach are described. The paper then focuses on the first step corresponding to Monte Carlo simulation of the primary interaction. The characteristics of the Primary Knock-On Atom (PKA) generated by neutron- or proton-silicon interactions for different energies are explored, analyzing in particular the PKA range in energies and species. This leads to the selection of 1 and 10 keV silicon atoms as good candidates to best represent the displacement cascades generated by all PKA. These PKA characteristics will be used as input in the following Molecular Dynamics simulation step, developed in a separate paper to simulate the displacement cascade generation and evolution. Monte Carlo simulations are also performed in a geometry representative of an image sensor, analyzing the distribution of non-ionizing deposited energy. The obtained distributions appear very similar for incident neutrons from 3 to 18 MeV and incident protons of 200 MeV, in agreement with similarities observed in experimentally measured dark current distributions in image sensors. The effect of geometric parameters on these distributions is finally explored. [ABSTRACT FROM PUBLISHER]

In the last years, the success of kernel‐based regularisation techniques in solving impulse response modelling tasks has revived the interest on linear system identification. In this work, an alternative perspective on the same problem is introduced. Instead of relying on a Bayesian framework to include assumptions about the system in the definition of the covariance matrix of the parameters, here the prior knowledge is injected at the cost function level. The key idea is to define the regularisation matrix as a filtering operation on the parameters, which allows for a more intuitive formulation of the problem from an engineering point of view. Moreover, this results in a unified framework to model low‐pass, band‐pass and high‐pass systems, and systems with one or more resonances. The proposed filter‐based approach outperforms the existing regularisation method based on the TC and DC kernels, as illustrated by means of Monte Carlo simulations on several linear modelling examples. [ABSTRACT FROM AUTHOR]

This study deals with the state estimation problem for stochastic hybrid systems with event‐triggered sensor schedule. By employing the basic interacting multiple model (IMM) approach, a novel event‐triggered state estimator has been proposed for stochastic hybrid systems based on a closed‐loop schedule rule. To compute the mode probabilities in the IMM estimator, a set of sigma points are generated to produce the pseudo‐measurements when the sensor measurements are unavailable. Then, the event‐triggered state estimator is extended to develop a distributed estimator in the sense of linear minimum mean square error, where the fused estimates are used to implement the re‐initialisation in the interacting stage of the IMM estimator. The performance of proposed estimators is illustrated through the Monte Carlo simulations involving tracking a manoeuvring target in the two‐dimensional experiment. Simulation results show that the performance of the proposed estimator is compared with that of the existing filter with a reduced computational burden. [ABSTRACT FROM AUTHOR]

Purpose: The first main aim of this study was to illustrate the absorbed dose rate distribution from 177Lu in sections of xenografted prostate cancer (PCa) tumors using high resolution digital autoradiography (DAR) and compare it with hypothetical identical radioactivity distributions of 90Y or 7 MeV alpha-particles. Three dosimetry models based on either dose point kernels or Monte Carlo simulations were used and evaluated. The second and overlapping aim, was to perform DAR imaging and dosimetric analysis of the distribution of radioactivity, and hence the absorbed dose rate, in tumor sections at an early time point after injection during radioimmunotherapy using 177Lu-h11B6, directed against the human kallikrein 2 antigen. Methods: Male immunodeficient BALB/c nude mice, aged 6-8 w, were inoculated by subcutaneous injection of ~107 LNCaP cells in a 200 µl suspension of a 1:1 mixture of medium and Matrigel. The antibody h11B6 was conjugated with the chelator CHX-A''-DTPA after which conjugated h11B6 was mixed with 177LuCl3. The incubation was performed at room temperature for 2 h, after which the labeling was terminated and the solution was purified on a NAP-5 column. About 20 MBq 177Lu-h11B6 was injected intravenously in the tail vein. At approximately 10 h postinjection (hpi), the mice were sacrificed and one tumor was collected from each of the five animals and cryosectioned into 10 μm thick slices. The tumor slices were measured and imaged using the DAR MicroImager system and the M3Vision software. Then the absorbed dose rate was calculated using a dose point kernel generated with the Monte Carlo code GATE v7.0. Results: The DAR system produced high resolution images of the radioactivity distribution, close to the resolution of single PCa cells. The DAR images revealed a pronounced heterogeneous radioactivity distribution, i.e., count rate per area, in the tumors, indicated by the normalized intensity variations along cross sections as mean ± SD: 0.15±0.15, 0.20±0.18, 0.12±0.17, 0.15±0.16, and 0.23±0.22, for each tumor section, respectively. The absorbed dose rate distribution for 177Lu at the time of dissection 10 hpi showed a maximum value of 2.9±0.4 Gy/h (mean ± SD), compared to 6.0±0.9 and 159±25 Gy/h for the hypothetical 90Y and 7 MeV alpha-particle cases assuming the same count rate densities. Mean absorbed dose rate values were 0.13, 0.53, and 6.43 Gy/h for 177Lu, 90Y, and alpha-particles, respectively. Conclusions: The initial uptake of 177Lu-h11B6 produces a high absorbed dose rate, which is important for a successful therapeutic outcome. The hypothetical 90Y case indicates a less heterogeneous absorbed dose rate distribution and a higher mean absorbed dose rate compared to 177Lu, although with a potentially increased irradiation of surrounding healthy tissue. The hypothetical alpha-particle case indicates the possibility of a higher maximum absorbed dose rate, although with a more heterogeneous absorbed dose rate distribution. [ABSTRACT FROM AUTHOR]

Purpose: To present and evaluate an ion chamber-based method for the cross-calibration between sites of activity measurements of unsealed radionuclides. Notably, the method allows direct comparison of short lived (i.e., clinically used) radioisotopes and the cross-calibration of radionuclide activity meters (also known as "dose calibrators"). Methods: A portable ion chamber has been designed which is easily shipped between sites, e.g., between a standards laboratory and a nuclear medicine department. The cylindrical chamber accommodates a syringe filled with unsealed radionuclide. Low background and staff shielding are achieved by designing the ion chamber small enough to fit into the well of a dose calibrator. The chamber's sensitivity for the clinically important unsealed radioisotopes 99mTc, 131I, and 18F was measured and compared to Monte Carlo calculations. The influence of syringe fill volume, positioning, and construction (wall diameter, length) was also investigated using Monte Carlo simulations. The chamber's linearity was measured over 5.5 orders of magnitude and its constancy tested over a period of >14.5 months. An overall uncertainty budget is presented. Results: Measured chamber sensitivity was 12.1 pA/100 MBq, 12.5 pA/100 MBq and 29.4 pA/100 MBq for 131I, 99mTc, and 18F, respectively. The uncertainty budget for the ion chamber alone yields an overall uncertainty of less than 1%, with the greatest contribution arising from constancy and linearity (0.5% each). Strategies to further reduce uncertainties are discussed. Conclusions: The investigation presented in this paper confirms the feasibility of the concept introduced here. To optimize its practical implementation, the concept would benefit from computerization for the purpose of data acquisition, evaluation, processing, and storage of measured values. [ABSTRACT FROM AUTHOR]

Purpose: An x-ray photon interacts with photon counting detectors (PCDs) and generates an electron charge cloud or multiple clouds. The clouds (thus, the photon energy) may be split between two adjacent PCD pixels when the interaction occurs near pixel boundaries, producing a count at both of the pixels. This is called double-counting with charge sharing. (A photoelectric effect with K-shell fluorescence x-ray emission would result in double-counting as well). As a result, PCD data are spatially and energetically correlated, although the output of individual PCD pixels is Poisson distributed. Major problems include the lack of a detector noise model for the spatio-energetic cross talk and lack of a computationally efficient simulation tool for generating correlated Poisson data. A Monte Carlo (MC) simulation can accurately simulate these phenomena and produce noisy data; however, it is not computationally efficient. Methods: In this study, the authors developed a new detector model and implemented it in an efficient software simulator that uses a Poisson random number generator to produce correlated noisy integer counts. The detector model takes the following effects into account: (1) detection efficiency; (2) incomplete charge collection and ballistic effect; (3) interaction with PCDs via photoelectric effect (with or without K-shell fluorescence x-ray emission, which may escape from the PCDs or be reabsorbed); and (4) electronic noise. The correlation was modeled by using these two simplifying assumptions: energy conservation and mutual exclusiveness. The mutual exclusiveness is that no more than two pixels measure energy from one photon. The effect of model parameters has been studied and results were compared withMCsimulations. The agreement, with respect to the spectrum, was evaluated using the reduced χ² statistics or a weighted sum of squared errors, χ² red (≥1), where χ² red = 1 indicates a perfect fit. Results: The model produced spectra with flat field irradiation that qualitatively agree with previous studies. The spectra generated with different model and geometry parameters allowed for understanding the effect of the parameters on the spectrum and the correlation of data. The agreement between the model and MC data was very strong. The mean spectra with 90 keV and 140 kVp agreed exceptionally well: χ² red values were 1.049 with 90 keV data and 1.007 with 140 kVp data. The degrees of cross talk (in terms of the relative increase from single pixel irradiation to flat field irradiation) were 22% with 90 keV and 19% with 140 kVp for MC simulations, while they were 21% and 17%, respectively, for the model. The covariance was in strong agreement qualitatively, although it was overestimated. The noisy data generation was very efficient, taking less than a CPU minute as opposed to CPU hours for MC simulators. Conclusions: The authors have developed a novel, computationally efficient PCD model that takes into account double-counting and resulting spatio-energetic correlation between PCD pixels. The MC simulation validated the accuracy. [ABSTRACT FROM AUTHOR]

Purpose: To introduce a fast ray-tracing algorithm in pencil proton radiography (PR) with a multilayer ionization chamber (MLIC) for in vivo range error mapping. Methods: Pencil beam PR was obtained by delivering spots uniformly positioned in a square (45×45 mm² field-of-view) of 9×9 spots capable of crossing the phantoms (210 MeV). The exit beam was collected by a MLIC to sample the integral depth dose (IDDMLIC). PRs of an electrondensity and of a head phantom were acquired by moving the couch to obtain multiple 45×45 mm² frames. To map the corresponding range errors, the two-dimensional set of IDDMLIC was compared with (i) the integral depth dose computed by the treatment planning system (TPS) by both analytic (IDDTPS) and Monte Carlo (IDDMC) algorithms in a volume of water simulating the MLIC at the CT, and (ii) the integral depth dose directly computed by a simple ray-tracing algorithm (IDDdirect) through the same CT data. The exact spatial position of the spot pattern was numerically adjusted testing different in-plane positions and selecting the one that minimized the range differences between IDDdirect and IDDMLIC. Results: Range error mapping was feasible by both the TPS and the ray-tracing methods, but very sensitive to even small misalignments. In homogeneous regions, the range errors computed by the direct ray-tracing algorithm matched the results obtained by both the analytic and the Monte Carlo algorithms. In both phantoms, lateral heterogeneities were better modeled by the ray-tracing and the Monte Carlo algorithms than by the analytic TPS computation. Accordingly, when the pencil beam crossed lateral heterogeneities, the range errors mapped by the direct algorithm matched better the Monte Carlo maps than those obtained by the analytic algorithm. Finally, the simplicity of the ray-tracing algorithm allowed to implement a prototype procedure for automated spatial alignment. Conclusions: The ray-tracing algorithm can reliably replace the TPS method in MLIC PR for in vivo range verification and it can be a key component to develop software tools for spatial alignment and correction of CT calibration. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the spatial resolution of proton CT using both a prototype proton CT scanner and Monte Carlo simulations. Methods: A custom cylindrical edge phantom containing twelve tissue-equivalent inserts with four different compositions at varying radial displacements from the axis of rotation was developed for measuring the modulation transfer function (MTF) of a prototype proton CT scanner. Two scans of the phantom, centered on the axis of rotation, were obtained with a 200 MeV, low-intensity proton beam: one scan with steps of 4°, and one scan with the phantom continuously rotating. In addition, Monte Carlo simulations of the phantom scan were performed using scanners idealized to various degrees. The data were reconstructed using an iterative projection method with added total variation superiorization based on individual proton histories. Edge spread functions in the radial and azimuthal directions were obtained using the oversampling technique. These were then used to obtain the modulation transfer functions. The spatial resolution was defined by the 10% value of the modulation transfer function (MTF10%) in units of line pairs per centimeter (lp/cm). Data from the simulations were used to better understand the contributions of multiple Coulomb scattering in the phantom and the scanner hardware, as well as the effect of discretization of proton location. Results: The radial spatial resolution of the prototype proton CT scanner depends on the total path length, W, of the proton in the phantom, whereas the azimuthal spatial resolution depends both on W and the position, u-, at which the most-likely path uncertainty is evaluated along the path. For protons contributing to radial spatial resolution, W varies with the radial position of the edge, whereas for protons contributing to azimuthal spatial resolution, W is approximately constant. For a pixel size of 0.625 mm, the radial spatial resolution of the image reconstructed from the fully idealized simulation data ranged between 6.31±0.36 lp/cm for W = 197 mm i.e., close to the center of the phantom, and 13.79±0.36 lp/cm for W = 97 mm, near the periphery of the phantom. The azimuthal spatial resolution ranged from 6.99±0.23 lp/cm at u_ = 75 mm (near the center) to 11.20±0.26 lp/cm at u_ = 20 mm (near the periphery). Multiple Coulomb scattering limits the radial spatial resolution for path lengths greater than approximately 130 mm, and the azimuthal spatial resolution for positions of evaluation greater than approximately 40 mm for W = 199 mm. The radial spatial resolution of the image reconstructed from data from the 4° stepped experimental scan ranged from 5.11±0.61 lp/cm forW = 197 mm to 8.58±0.50 lp/cm forW = 97 mm. In the azimuthal direction, the spatial resolution ranged from 5.37±0.40 lp/cm at u_ = 75 mm to 7.27±0.39 lp/cm at u_ = 20 mm. The continuous scan achieved the same spatial resolution as that of the stepped scan. Conclusions: Multiple Coulomb scattering in the phantom is the limiting physical factor of the achievable spatial resolution of proton CT; additional loss of spatial resolution in the prototype system is associated with scattering in the proton tracking system and inadequacies of the proton path estimate used in the iterative reconstruction algorithm. Improvement in spatial resolution may be achievable by improving the most likely path estimate by incorporating information about high and low density materials, and by minimizing multiple Coulomb scattering in the proton tracking system. [ABSTRACT FROM AUTHOR]

Purpose: A practical means of delivering both therapeutic radiation and hyperthermia to a deepseated target has been identified in the literature as highly desirable, provided it is capable of generating sufficient temperatures over the defined target volume. The authors present continued development of a dual-modality thermobrachytherapy (TB) seed, investigating its capabilities in delivering prescribed hyperthermia to realistic deep-seated targets. Methods: The TB seed is based on the ubiquitous low dose-rate (LDR) brachytherapy permanent implant. Heat is generated by incorporating a ferromagnetic core within the seed and placing the patient in an oscillating external magnetic field, producing eddy currents within the core and hence Joule heating. A strategically selected Curie temperature results in thermal self-regulation. The magnetic and thermal properties of the TB seed were studied experimentally by means of seed prototypes placed in a tissue-mimicking phantom and heated with an industrial induction heater, as well as computationally in the finite element analysis solver COMSOL Multiphysics. Patient-specific seed distributions derived from LDR permanent prostate implants previously conducted at their institution were modeled in COMSOL to evaluate their ability to adequately cover a defined target volume and to overcome the loss of heat due to blood perfusion within tissue. The calculated temperature distributions were analyzed by generating temperature-volume histograms, which were used to quantify coverage and temperature homogeneity for varied blood perfusion rates, seed Curie temperatures, and thermal power production rates. Use of additional hyperthermia-only (HT-only) seeds in unused spots within the implantation needles was investigated, as was an increase in these seeds' core size to increase their power. The impact of the interseed attenuation and scatter (ISA) effect on radiation dose distributions of this seed was also quantified by Monte Carlo studies in the software package Monte Carlo N-Particle Version 5. Results: Increasing the power production of the seeds, as well as increasing their Curie point, would increase the maximum blood perfusion rate that a given seed distribution could overcome to obtain an acceptable temperature distribution. However, this would also increase the maximum temperatures generated at the seed surfaces. Auxiliary HT-only seeds serve to improve the temperature uniformity within the target, as well as decrease the seed power generation requirements. Both an increase in their core size and an increase in both seed types' Curie temperatures enhance the resulting temperature coverage. The interseed and scatter effect caused by both the TB and HT-only seeds was found to reduce the dose to 90% of the target volume (D90) by a factor of 1.10±0.02. Conclusions: A systematic approach of combining LDR prostate brachytherapy with hyperthermia is described, and its ability to provide sufficient and uniform temperature distributions in realistic patient-specific implants evaluated. A combination of TB and HT-only seeds may be used to produce a uniform temperature distribution in a defined target. Various modeled changes to their design, such as optimization of their Curie temperature, improve their ability to overcome the thermal effects of blood perfusion. The enhanced ISA of the TB and HT-only seeds must be taken into account for dose calculations, but is manageable. [ABSTRACT FROM AUTHOR]

Purpose: Proton beam dosimetry using bare plastic optical fibers has emerged as a simple approach to proton beam dosimetry. The source of the signal in this method has been attributed to C? erenkov radiation. The aim of this work was a phenomenological study of the nature of the visible light responsible for the signal in bare fiber optic dosimetry of proton therapy beams. Methods: Plastic fiber optic probes embedded in solid water phantoms were irradiated with proton beams of energies 100, 180, and 225 MeV produced by a proton therapy cyclotron. Luminescence spectroscopy was performed by a CCD-coupled spectrometer. The spectra were acquired at various depths in phantom to measure the percentage depth dose (PDD) for each beam energy. For comparison, the PDD curves were acquired using a standard multilayer ion chamber device. In order to further analyze the contribution of the C? erenkov radiation in the spectra, Monte Carlo simulation was performed using ????? Monte Carlo code to stochastically simulate radiation transport, ionizing radiation dose deposition, and optical emission of C? erenkov radiation. Results: The measured depth doses using the bare fiber are in agreement with measurements performed by the multilayer ion chamber device, indicating the feasibility of using bare fiber probes for proton beam dosimetry. The spectroscopic study of proton-irradiated fibers showed a continuous spectrum with a shape different from that of C? erenkov radiation. The Monte Carlo simulations confirmed that the amount of the generated C? erenkov light does not follow the radiation absorbed dose in a medium. Conclusions: The source of the optical signal responsible for the proton dose measurement using bare optical fibers is not C? erenkov radiation. It is fluorescence of the plastic material of the fiber. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to develop a Monte Carlo simulation model for in vivo associated particle neutron elemental imaging (APNEI) and to study the feasibility of using APNEI to determine the iron distribution in a human liver with the defined model. Methods: The model presented in this study was defined in ???? by the basic geometry of the human body, the use of D+D source neutrons, iron as the element of interest, an iron-containing voxel in the liver as the target region, and 2 large germanium detectors anterior and posterior to the trunk of the body. The f 8 pulse height tally was employed in ???? to determine the signal acquired from iron inelastic scatter gamma rays at various iron concentrations in the target liver voxel. Correspondingly, the f 4 average flux tally in ???? was modified by a dose function such that the equivalent dose to the whole liver and the effective dose to the whole body could be estimated and used as the basis for a limiting number of neutron histories which could feasibly allow for the collection of a sufficient volume of data to construct a 2D image of iron distribution in the liver voxel. Results: Assuming an allowable equivalent dose to the liver of 5 mSv, 143 inelastic scatter iron gamma ray counts (at ~847 keV) would ideally be registered at the germanium detectors for a 1 cm³ cube-shaped liver voxel with an iron concentration of 1000 ppm. According to the simulation model, an image of iron distribution in the liver can be constructed with a 1 cm resolution at the level of 1000 ppm iron. Collecting such an image would yield an estimated whole body dose of 0.82 mSv. The mathematical introduction of image uncertainty resulting from source spot diameter and detector timing resolution more closely approximates the result of real world application. Conclusions: APNEI of certain elements in vivo appears feasible given several timing, sensitivity, and resolution caveats. However, further study is required to determine what the detection limit of iron would be and what image resolution would be in an experimental setup as the present model contains idealized assumptions which overestimate the signal attributable to iron inelastic scatter gamma rays. [ABSTRACT FROM AUTHOR]

Purpose: Magnetic resonance imaging (MRI)-guided Co-60 provides daily and intrafractional MRI soft tissue imaging for improved target and critical organ tracking. To increase delivery efficiency, the system uses three Co-60 sources at 120? apart, allowing up to 600 cGy combined dose rate at isocenter. Despite the potential tripling in output, creating a delivery plan that uses all three sources is considerably unintuitive. Here, the authors computerize the triplet orientation optimization using column generation, an approach that was demonstrated effective in integrated beam orientation and fluence optimization for noncoplanar therapies. To achieve a better plan quality without increasing the treatment time, the authors then solve a fluence map optimization (FMO) problem while regularizing the fluence maps to reduce the number of deliverable MLC segments. Methods: Three patients--one prostate, one lung, and one head and neck boost plan (H&NBoost)-- were evaluated in this study. For each patient, the beamlet doses were calculated using Monte Carlo, under a 0.35 T magnetic field, for 180 equally spaced coplanar beams grouped into 60 triplets. The beamlet size is 1.05×0.5 cm determined by the MLC leaf thickness and step size. The triplets were selected using the column generation algorithm. The FMO problem was formulated using an L2-norm dose fidelity term and an L1-norm anisotropic total variation regularization term, which allows controlling the number of MLC segments, and hence the treatment time, with minimal degradation to the dose. The authors' Fluence Regularization and Optimized Selection of Triplets (FROST) plans were compared against the clinical treatment plans (CLNs) produced by an experienced dosimetrist. PTV homogeneity, max dose, mean dose, D95, D98, and D99 were evaluated. OAR max and mean doses, as well as R50, defined as the ratio of the 50% isodose volume over the planning target volume were investigated. Results: The mean PTV D95, D98, and D99 differ by +0.04%, +0.07%, and +0.25% of the prescription dose between planning methods. The mean PTV homogeneity was virtually same with values at 0.8788 (FROST) and 0.8812 (CLN). R50 decreased by 0.67 comparing FROST to CLN. On average, FROST reduced Dmax and Dmean of OARs by 7.30% and 6.08% of the prescription dose, respectively. The manual CLN planning processes required numerous trial and error runs. The FROST plans on the other hand required minimal human intervention. Conclusions: Efficient delivery of MRI-guided Co-60 therapy needs the output of multiple sources yet suffers from unintuitive and laborious manual beam selection processes. Computerized triplet orientation optimization improves both planning efficiency and plan dosimetry. The novel fluence map regularization provides additional controls over the number of MLC segments and treatment time. [ABSTRACT FROM AUTHOR]

Purpose: Small field measurements are challenging, due to the physical characteristics coming from the lack of charged particle equilibrium, the partial occlusion of the finite radiation source, and to the detector response. These characteristics can be modeled in the dose calculations in the treatment planning systems. Aim of the present work is to evaluate the MU calculation accuracy for small fields, defined by jaw or MLC, for anisotropic analytical algorithm (AAA) and Acuros XB algorithms, relative to output measurements on the beam central axis. Methods: Single point output factor measurement was acquired with a PTW microDiamond detector for 6 MV, 6 and 10 MV unflattened beams generated by a Varian TrueBeam STx equipped with high definition-MLC. Fields defined by jaw or MLC apertures were set; jaw-defined: 0.6×0.6, 0.8×0.8, 1×1, 2×2, 3×3, 4×4, 5×5, and 10×10 cm²; MLC-defined: 0.5×0.5 cm² to the maximum field defined by the jaw, with 0.5 cm stepping, and jaws set to: 2×2, 3×3, 4×4, 5×5, and 10×10 cm². MU calculation was obtained with 1 mm grid in a virtual water phantom for the same fields, for AAA and Acuros algorithms implemented in the Varian ECLIPSE treatment planning system (version 13.6). Configuration parameters as the effective spot size (ESS) and the dosimetric leaf gap (DLG) were varied to find the best parameter setting. Differences between calculated and measured doses were analyzed. Results: Agreement better than 0.5% was found for field sizes equal to or larger than 2×2 cm² for both algorithms. A dose overestimation was present for smaller jaw-defined fields, with the best agreement, averaged over all the energies, of 1.6% and 4.6% for a 1×1 cm² field calculated by AAA and Acuros, respectively, for a configuration with ESS = 1 mm for both X and Y directions for AAA, and ESS = 1.5 and 0 mm for X and Y directions for Acuros. Conversely, a calculated dose underestimation was found for small MLC-defined fields, with the best agreement averaged over all the energies, of -3.9% and 0.2% for a 1×1 cm² field calculated by AAA and Acuros, respectively, for a configuration with ESS = 0 mm for both directions and both algorithms. Conclusions: For optimal setting applied in the algorithm configuration phase, the agreement of Acuros calculations with measurements could achieve the 3% for MLC-defined fields as small as 0.5×0.5 cm². Similar agreement was found for AAA for fields as small as 1×1 cm². [ABSTRACT FROM AUTHOR]

Purpose: Inaccurate density information may introduce dose calculation errors when inhomogeneity correction is applied. The aim of the present study was to examine the effect of density variation on photon dose calculation accuracy using the convolution/superposition (CS) algorithm with the focus on newer treatment technologies including intensity modulated radiotherapy, volumetric modulated arc radiotherapy, and stereotactic body radiotherapy (SBRT). Methods: Calculations were first performed using simple inhomogeneity phantoms in order to determine clinically relevant tolerance levels for different tissue types. The clinical validity of these tolerance levels was then demonstrated by evaluating their dosimetric impact on clinical treatment plans. The dose difference was examined by comparing the dose-volume histogram statistics and the spatial distribution of dose errors calculated on a voxel-by-voxel basis. In order to gain some insight into this issue for the Monte Carlo (MC) algorithm, the authors also performed additional validation using a MC dose calculation system. Results: For soft tissue and bone, the tolerance levels determined from this study appear to be consistent with the values previously calculated using simpler inhomogeneity correction methods. However, the tolerance level for low density lung tissue has been found to be much smaller than what previous studies had reported. The results from this study also suggest that if density variation is restricted within ±0.02, ±0.03, and ±0.10 g/cm³ for lung, soft tissue, and bone, respectively, the resulting dose error in target volumes can be limited to <2% for most clinical cases and <3% for more challenging lung SBRT cases. When the same amount of density variation is introduced, MC algorithm yields ~0.3%-0.9% and ~0.0%-1.2% smaller dose errors for the target and organs-at-risk as compared to CS. Conclusions: It is important to include lung substitute material into the periodic quality assurance of CT simulators and treatment planning systems. This study suggests that the tolerance value of CT number for lung material is ~±20 HU in order to keep the associated dose uncertainty at 2%-3% or less. Further studies with larger number of lung cases are warranted to validate this new tolerance value before it can be applied to clinical practice. [ABSTRACT FROM AUTHOR]

Purpose: CyberKnife system is initially equipped with fixed circular cones for stereotactic radiosurgery. Two dose calculation algorithms, Ray-Tracing and Monte Carlo, are available in the supplied treatment planning system. A multileaf collimator system was recently introduced in the latest generation of system, capable of arbitrarily shaped treatment field. The purpose of this study is to develop a model based dose calculation algorithm to better handle the lateral scatter in an irregularly shaped small field for the CyberKnife system. Methods: A pencil beam dose calculation algorithm widely used in linac based treatment planning system was modified. The kernel parameters and intensity profile were systematically determined by fitting to the commissioning data. The model was tuned using only a subset of measured data (4 out of 12 cones) and applied to all fixed circular cones for evaluation. The root mean square (RMS) of the difference between the measured and calculated tissue-phantom-ratios (TPRs) and off-center-ratio (OCR) was compared. Three cone size correction techniques were developed to better fit the OCRs at the penumbra region, which are further evaluated by the output factors (OFs). The pencil beam model was further validated against measurement data on the variable dodecagon-shaped Iris collimators and a half-beam blocked field. Comparison with Ray-Tracing and Monte Carlo methods was also performed on a lung SBRT case. Results: The RMS between the measured and calculated TPRs is 0.7% averaged for all cones, with the descending region at 0.5%. The RMSs of OCR at infield and outfield regions are both at 0.5%. The distance to agreement (DTA) at the OCR penumbra region is 0.2 mm. All three cone size correction models achieve the same improvement in OCR agreement, with the effective source shift model (SSM) preferred, due to their ability to predict more accurately the OF variations with the source to axis distance (SAD). In noncircular field validation, the pencil beam calculated results agreed well with the film measurement of both Iris collimators and the half-beam blocked field, fared much better than the Ray-Tracing calculation. Conclusions: The authors have developed a pencil beam dose calculation model for the CyberKnife system. The dose calculation accuracy is better than the standard linac based system because the model parameters were specifically tuned to the CyberKnife system and geometry correction factors. The model handles better the lateral scatter and has the potential to be used for the irregularly shaped fields. Comprehensive validations on MLC equipped system are necessary for its clinical implementation. It is reasonably fast enough to be used during plan optimization. [ABSTRACT FROM AUTHOR]

A two-dimensional Ising model with nearest-neighbors ferromagnetic interactions is implemented in a Field Programmable Gate Array (FPGA) board. Extensive Monte Carlo simulations were carried out using an efficient hardware representation of individual spins and a combined global-local LFSR random number generator. Consistent results regarding the descriptive properties of magnetic systems, like energy, magnetization and susceptibility are obtained while a speed-up factor of approximately six times is achieved in comparison to previous FPGA-based published works and almost $10^4$ times in comparison to a standard CPU simulation. A detailed description of the logic design used is given together with a careful analysis of the quality of the random number generator used. The obtained results confirm the potential of FPGAs for analyzing the statistical mechanics of magnetic systems. [ABSTRACT FROM AUTHOR]

Purpose: Small field output correction factors have been studied by several research groups for the PTW 60019 microDiamond (MD) dosimeter, by comparing the response of such a device with both reference dosimeters and Monte Carlo simulations. A general good agreement is observed for field sizes down to about 1 cm. However, evident inconsistencies can be noticed when comparing some experimental results and Monte Carlo simulations obtained for smaller irradiation fields. This issue was tentatively attributed by some authors to unintentional large variations of the MD active surface area. The aim of the present study is a nondestructive experimental determination of the MD active surface area and active volume. Methods: Ten MD dosimeters, one MD prototype, and three synthetic diamond samples were investigated in the present work. 2D maps of the MD response were recorded under scanned soft x-ray microbeam irradiation, leading to an experimental determination of the device active surface area. Profiles of the device responses were measured as well. In order to evaluate the MD active volume, the thickness of the diamond sensing layer was independently evaluated by capacitance measurements and alpha particle detection experiments. The MD sensitivity, measured at the PTW calibration laboratory, was also used to calculate the device active volume thickness. Results: An average active surface area diameter of (2.19±0.02) mm was evaluated by 2D maps and response profiles of all the MDs. Average active volume thicknesses of (1.01±0.13) µm and (0.97±0.14) µm were derived by capacitance and sensitivity measurements, respectively. The obtained results are well in agreement with the nominal values reported in the manufacturer dosimeter specifications. A homogeneous response was observed over the whole device active area. Besides the one from the device active volume, no contributions from other components of the housing nor from encapsulation materials were observed in the 2D response maps. Conclusions: The obtained results demonstrate the high reproducibility of the MD fabrication process. The observed discrepancies among the output correction factors reported by several authors for MD response in very small fields are very unlikely to be ascribed to unintentional variations of the device active surface area and volume. It is the opinion of the authors that the role of the volume averaging as well as of other perturbation effects should be separately investigated instead, both experimentally and by Monte Carlo simulations, in order to better clarify the behaviour of the MD response in very small fields. [ABSTRACT FROM AUTHOR]

Purpose: This study introduces a novel autocontouring algorithm based on particle filter for lung tumors. It is validated on dynamic magnetic resonance (MR) images and is developed in the context of MR-linac treatments. Methods: A sequential Monte Carlo method called particle filter is used as the main structure of the algorithm and is combined with Otsu's thresholding technique to contour lung tumors on dynamic MR images. Four non-small cell lung cancer (NSCLC) patients were imaged with a 1.5 T MR for 60 s at a rate of 4 images/s and were asked to breathe normally. Prior to treatment, some image processing is required by the proposed algorithm, which includes a manual contour of the tumor, the tumor's displacement, and its descriptive statistics. During treatment, the contours are automatically generated by thresholding around the center of mass of the particles. A comparison with the expert's contours is obtained by calculating the Dice similarity coefficient (DSC), the precision, the recall, the Hausdorff distance, and the difference in centroid positions (Δd). Results: This autocontouring algorithm is independent of pretreatment training and presents continuous adaptability as provided by the nature of particle filters. The number of particles is proportional to the area of the tumor and increases the computational time at a rate of 2 ms for every 500 particles, whereas the contouring step adds a constant 14 ms. The contours' comparison is obtained with a mean DSC of 0.89-0.91, mean precision of 0.88-0.91, mean recall of 0.89-0.95, and mean Δd of 0.6-2.0 mm. Conclusions: This work presents a proof of concept of a new autocontouring algorithm for NSCLC patients on dynamic MR images. The contours were generated in good agreement with the expert's contours. [ABSTRACT FROM AUTHOR]

In this study, the blind despreading of long‐code direct sequence spread spectrum signals (LC‐DSSS) is considered. Qiu et al. presented a heuristic segmentation‐based method to estimate the spreading code of LC‐DSSS signals, which divided the received signal into far shorter temporal windows than the symbol duration, then spreading code was reconstructed from these short windows by computing the related covariance matrices. However, Qiu et al. did not consider the criterion of determining the segmentation length. By combining the matrix perturbation theory and run length property, the authors propose a run‐length method for determining the segmentation length based on the segmentation idea, and this method can also be applied to long‐code direct‐sequence code division multiple access (LC‐DS‐CDMA) signals. Monte Carlo simulations for both LC‐DSSS signals and LC‐DS‐CDMA signals are presented to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Purpose: Compton cameras (CCs) use electronic collimation to reconstruct the images of activity distribution. Although this approach can greatly improve imaging efficiency, due to complex geometry of the CC principle, image reconstruction with the standard iterative algorithms, such as ordered subset expectation maximization (OSEM), can be very time-consuming, even more so if resolution recovery (RR) is implemented. We have previously shown that the origin ensemble (OE) algorithm can be used for the reconstruction of the CC data. Here we propose a method of extending our OE algorithm to include RR. Methods: To validate the proposed algorithm we used Monte Carlo simulations of a CC composed of multiple layers of pixelated CZT detectors and designed for imaging small animals. A series of CC acquisitions of small hot spheres and the Derenzo phantom placed in air were simulated. Images obtained from (a) the exact data, (b) blurred data but reconstructed without resolution recovery, and (c) blurred and reconstructed with resolution recovery were compared. Furthermore, the reconstructed contrast-to-background ratios were investigated using the phantom with nine spheres placed in a hot background. Results: Our simulations demonstrate that the proposed method allows for the recovery of the resolution loss that is due to imperfect accuracy of event detection. Additionally, tests of camera sensitivity corresponding to different detector configurations demonstrate that the proposed CC design has sensitivity comparable to PET. When the same number of events were considered, the computation time per iteration increased only by a factor of 2 when OE reconstruction with the resolution recovery correction was performed relative to the original OE algorithm. We estimate that the addition of resolution recovery to the OSEM would increase reconstruction times by 2-3 orders of magnitude per iteration. Conclusions: The results of our tests demonstrate the improvement of image resolution provided by the OE reconstructions with resolution recovery. The quality of images and their contrast are similar to those obtained from the OE reconstructions from scans simulated with perfect energy and spatial resolutions. [ABSTRACT FROM AUTHOR]

Purpose: Gold nanoparticles (GNPs) are being investigated actively for various applications in cancer diagnosis and therapy. As an effort to improve the imaging of GNPs in vivo, the authors developed bimetallic hybrid Zn@Au NPs with zinc cores and gold shells, aiming to render them in vivo visibility through positron emission tomography (PET) after the proton activation of the zinc core as well as capability to induce radiosensitization through the secondary electrons produced from the gold shell when irradiated by various radiation sources. Methods: Nearly spherical zinc NPs (~5-nm diameter) were synthesized and then coated with a ~4.25-nm gold layer to make Zn@Au NPs (~13.5-nm total diameter). 28.6 mg of these Zn@Au NPs was deposited (~100 μm thick) on a thin cellulose target and placed in an aluminum target holder and subsequently irradiated with 14.15-MeV protons from a GE PETtrace cyclotron with 5-μA current for 5 min. After irradiation, the cellulose matrix with the NPs was placed in a dose calibrator to assess the induced radioactivity. The same procedure was repeated with 8-MeV protons. Gamma ray spectroscopy using an high-purity germanium detector was conducted on a very small fraction (<1 mg) of the irradiated NPs for each proton energy. In addition to experimental measurements, Monte Carlo simulations were also performed with radioactive Zn@Au NPs and solid GNPs of the same size irradiated with 160-MeV protons and 250-kVp x-rays. Results: The authors measured 168 μCi of activity 32 min after the end of bombardment for the 14.15-MeV proton energy sample using the 66Ga setting on a dose calibrator; activity decreased to 2 μCi over a 24-h period. For the 8-MeV proton energy sample, PET imaging was additionally performed for 5 min after a 12-h delay. A 12-h gamma ray spectrum showed strong peaks at 511 keV (2.05×106 counts) with several other peaks of smaller magnitude for each proton energy sample. PET imaging showed strong PET signals from mostly decaying 66Ga. The Monte Carlo results showed that radioactive Zn@Au NPs and solid GNPs provided similar characteristics in terms of their secondary electron spectra when irradiated. Conclusions: The Zn@Au NPs developed in this investigation have the potential to be used as PET-imageable radiosensitizers for radiotherapy applications as well as PET tracers for molecular imaging applications. [ABSTRACT FROM AUTHOR]

Purpose: To quantify and explain the backscatter dose effects for clinically relevant high atomic number materials being irradiated in the presence of a 1.5 T transverse magnetic field. Methods: Interface effects were investigated using Monte Carlo simulation techniques. We used GPUMCD (v5.1) and geant4 (v10.1) for this purpose. GPUMCD is a commercial software written for the Elekta AB, MRI linac. Dose was scored using GPUMCD in cubic voxels of side 1 and 0.5 mm, in two different virtual phantoms of dimensions 20 ? 20 ? 20 cm and 5 ? 5 ? 13.3 cm, respectively. A photon beam was generated from a point 143.5 cm away from the isocenter with energy distribution sampled from a histogram representing the true Elekta, MRI linac photon spectrum. A slab of variable thickness and position containing either bone, aluminum, titanium, stainless steel, or one of the two different dental filling materials was inserted as an inhomogeneity in the 20 ? 20 ? 20 cm phantom. The 5 ? 5 ? 13.3 cm phantom was used as a clinical test case in order to explain the dose perturbation effects for a head and neck cancer patient. The back scatter dose factor (BSDF) was defined as the ratio of the doses at a given depth with and without the presence of the inhomogeneity. Backscattered electron fluence was calculated at the inhomogeneity interface using geant4. A 1.5 T magnetic field was applied perpendicular to the direction of the beam in both phantoms, identical to the geometry in the Elekta MRI linac. Results: With the application of a 1.5 T magnetic field, all the BSDF's were reduced by 12%-47%, compared to the no magnetic field case. The corresponding backscattered electron fluence at the interface was also reduced by 45%-64%. The reduction in the BSDF at the interface, due to the application of the magnetic field, is manifested in a different manner for each material. In the case of bone, the dose drops at the interface contrary to the expected increase when no magnetic field is applied. In the case of aluminum, the dose at the interface is the same with and without the presence of the aluminum. For all of the other materials the dose increases at the interface. Conclusions: The reduction in dose at the interface, in the presence of the magnetic field, is directly related to the reduction in backscattered electron fluence. This reduction occurs due to two different reasons. First, the electron spectrum hitting the interface is changed when the magnetic field is turned on, which results in changes in the electron scattering probability. Second, some electrons that have curved trajectories due to the presence of the magnetic field are absorbed by the higher density side of the interface and no longer contribute to the backscattered electron fluence. [ABSTRACT FROM AUTHOR]

Purpose: A semiempirical model for x-ray production in tungsten thick-targets was evaluated using a new characterization of electron fluence. Methods: Electron fluence is modeled taking into account both the energy and angular distributions, each of them adjusted to Monte Carlo simulated data. Distances were scaled by the CSDA range to reduce the energy dependence. Bremsstrahlung production was found by integrating the cross section with the fluence in a 1D penetration model. Characteristic radiation was added using a semiempirical law whose validity was checked. The results were compared the experimental results of Bhat et al., with the SpekCalc numerical tool, and with MCNPX simulation results from the work of Hernandez and Boone. Results: The model described shows better agreement with the experimental results than the SpekCalc predictions in the sense of area between the spectra. A general improvement of the predictions of half-value layers is also found. The results are also in good agreement with the simulation results in the 50--640 keV energy range. Conclusions: A complete model for x-ray production in thick bremsstrahlung targets has been developed, improving the results of previous works and extending the energy range covered to the 50--640 keV interval. [ABSTRACT FROM AUTHOR]

Adaptive notch filters have been the focus of intense research for more than three decades. Low computational requirements and good performance make them attractive for tracking frequency modulated signals. Despite the extensive literature on adaptive notch filters, algorithm extensions and new models for describing the dynamics of the notch frequency continue to be proposed. In this study, the equivalence between adaptive notch filters using a plain gradient (PG) algorithm and frequency lock loops (FLLs) with exponential filtering is established. FLL theory is then used to analyse the noise performance and signal tracking capabilities of adaptive notch filters. A linear model describing the dynamics of the filter adaptation process is derived and the concepts of loop and Doppler bandwidths are introduced. Criteria based on the loop and Doppler bandwidths are suggested to set the PG adaptation step. Finally, algorithm extensions based on the FLL theory are proposed. Theoretical results are supported by Monte Carlo simulations which show the validity of the analysis performed. [ABSTRACT FROM AUTHOR]

Purpose: To accurately and efficiently implement charged particle transport in a magnetic field in EGSnrc and validate the code for the use in phantom and ion chamber simulations. Methods: The effect of the magnetic field on the particle motion and position is determined using one- and three-point numerical integrations of the Lorentz force on the charged particle and is added to the condensed history calculation performed by the EGSnrc PRESTA-II algorithm. The code is tested with a Fano test adapted for the presence of magnetic fields. The code is compatible with all EGSnrc based applications, including egs++. Ion chamber calculations are compared to experimental measurements and the effect of the code on the efficiency and timing is determined. Results: Agreement with the Fano test's theoretical value is obtained at the 0.1% level for large step-sizes and in magnetic fields as strong as 5 T. The NE2571 dose calculations achieve agreement with the experiment within 0.5% up to 1 T beyond which deviations up to 1.2% are observed. Uniform air gaps of 0.5 and 1 mm and a misalignment of the incoming photon beam with the magnetic field are found to produce variations in the normalized dose on the order of 1%. These findings necessitate a clear definition of all experimental conditions to allow for accurate Monte Carlo simulations. It is found that ion chamber simulation times are increased by only 38%, and a 10 × 10 × 6 cm³ water phantom with (3 mm)³ voxels experiences a 48% increase in simulation time as compared to the default EGSnrc with no magnetic field. Conclusions: The incorporation of the effect of the magnetic fields in EGSnrc provides the capability to calculate high accuracy ion chamber and phantom doses for the use in MRI-radiation systems. Further, the effect of apparently insignificant experimental details is found to be accentuated by the presence of the magnetic field. [ABSTRACT FROM AUTHOR]

Purpose: The clinical commissioning of IMRT subject to a magnetic field is challenging. The purpose of this work is to develop a GPU-accelerated Monte Carlo dose calculation platform based on penelope and then use the platform to validate a vendor-provided MRIdian head model toward quality assurance of clinical IMRT treatment plans subject to a 0.35 T magnetic field. Methods: penelope was first translated from fortran to c++ and the result was confirmed to produce equivalent results to the original code. The c++ code was then adapted to cuda in a workflow optimized for GPU architecture. The original code was expanded to include voxelized transport with Woodcock tracking, faster electron/positron propagation in a magnetic field, and several features that make gpenelope highly user-friendly. Moreover, the vendor-provided MRIdian head model was incorporated into the code in an effort to apply gpenelope as both an accurate and rapid dose validation system. A set of experimental measurements were performed on the MRIdian system to examine the accuracy of both the head model and gpenelope. Ultimately, gpenelope was applied toward independent validation of patient doses calculated by MRIdian's kmc. Results: An acceleration factor of 152 was achieved in comparison to the original single-thread fortran implementation with the original accuracy being preserved. For 16 treatment plans including stomach (4), lung (2), liver (3), adrenal gland (2), pancreas (2), spleen(1), mediastinum (1), and breast (1), the MRIdian dose calculation engine agrees with gpenelope with a mean gamma passing rate of 99.1% ± 0.6% (2%/2 mm). Conclusions: A Monte Carlo simulation platform was developed based on a GPU- accelerated version of penelope. This platform was used to validate that both the vendor-provided head model and fast Monte Carlo engine used by the MRIdian system are accurate in modeling radiation transport in a patient using 2%/2 mm gamma criteria. Future applications of this platform will include dose validation and accumulation, IMRT optimization, and dosimetry system modeling for next generation MR-IGRT systems. [ABSTRACT FROM AUTHOR]

Purpose: The future of radiation therapy will require advanced inverse planning solutions to support single-arc, multiple-arc, and "4π" delivery modes, which present unique challenges in finding an optimal treatment plan over a vast search space, while still preserving dosimetric accuracy. The successful clinical implementation of such methods would benefit from Monte Carlo (MC) based dose calculation methods, which can offer improvements in dosimetric accuracy when compared to deterministic methods. The standard method for MC based treatment planning optimization leverages the accuracy of the MC dose calculation and efficiency of well-developed optimization methods, by precalculating the fluence to dose relationship within a patient with MC methods and subsequently optimizing the fluence weights. However, the sequential nature of this implementation is computationally time consuming and memory intensive. Methods to reduce the overhead of the MC precalculation have been explored in the past, demonstrating promising reductions of computational time overhead, but with limited impact on the memory overhead due to the sequential nature of the dose calculation and fluence optimization. The authors propose an entirely new form of "concurrent" Monte Carlo treat plan optimization: a platform which optimizes the fluence during the dose calculation, reduces wasted computation time being spent on beamlets that weakly contribute to the final dose distribution, and requires only a low memory footprint to function. In this initial investigation, the authors explore the key theoretical and practical considerations of optimizing fluence in such a manner. Methods: The authors present a novel derivation and implementation of a gradient descent algorithm that allows for optimization during MC particle transport, based on highly stochastic information generated through particle transport of very few histories. A gradient rescaling and renormalization algorithm, and the concept of momentum from stochastic gradient descent were used to address obstacles unique to performing gradient descent fluence optimization during MC particle transport. The authors have applied their method to two simple geometrical phantoms, and one clinical patient geometry to examine the capability of this platform to generate conformal plans as well as assess its computational scaling and efficiency, respectively. Results: The authors obtain a reduction of at least 50% in total histories transported in their investigation compared to a theoretical unweighted beamlet calculation and subsequent fluence optimization method, and observe a roughly fixed optimization time overhead consisting of ~10% of the total computation time in all cases. Finally, the authors demonstrate a negligible increase in memory overhead of ~7–8 MB to allow for optimization of a clinical patient geometry surrounded by 36 beams using their platform. Conclusions: This study demonstrates a fluence optimization approach, which could significantly improve the development of next generation radiation therapy solutions while incurring minimal additional computational overhead. [ABSTRACT FROM AUTHOR]

Purpose: This work evaluates Varian's electron phase–space sources for Monte Carlo simulation of the TrueBeam for modulated electron radiation therapy (MERT) and combined, modulated photon and electron radiation therapy (MPERT) where fields are shaped by the photon multileaf collimator (MLC) and delivered at 70 cm SSD. Methods: Monte Carlo simulations performed with EGSnrc-based BEAMnrc/DOSXYZnrc and PENELOPE-based PRIMO are compared against diode measurements for 5×5, 10×10, and 20×20 cm2 MLC-shaped fields delivered with 6, 12, and 20 MeV electrons at 70 cm SSD (jaws set to 40×40 cm2). Depth dose curves and profiles are examined. In addition, EGSnrc-based simulations of relative output as a function of MLC-field size and jaw-position are compared against ion chamber measurements for MLC-shaped fields between 3×3 and 25×25 cm2 and jaw positions that range from the MLC-field size to 40×40 cm2. Results: Percent depth dose curves generated by BEAMnrc/DOSXYZnrc and PRIMO agree with measurement within 2%, 2 mm except for PRIMO's 12 MeV, 20×20 cm2 field where 90% of dose points agree within 2%, 2 mm. Without the distance to agreement, differences between measurement and simulation are as large as 7.3%. Characterization of simulated dose parameters such as FWHM, penumbra width and depths of 90%, 80%, 50%, and 20% dose agree within 2 mm of measurement for all fields except for the FWHM of the 6 MeV, 20×20 cm2 field which falls within 2 mm distance to agreement. Differences between simulation and measurement exist in the profile shoulders and penumbra tails, in particular for 10×10 and 20×20 cm2 fields of 20 MeV electrons, where both sets of simulated data fall short of measurement by as much as 3.5%. BEAMnrc/DOSXYZnrc simulated outputs agree with measurement within 2.3% except for 6 MeV MLC-shaped fields. Discrepancies here are as great as 5.5%. Conclusions: TrueBeam electron phase–spaces available from Varian have been implemented in two distinct Monte Carlo simulation packages to produce dose distributions and outputs that largely reflect measurement. Differences exist in the profile shoulders and penumbra tails for the 20 MeV phase–space off-axis and in the outputs for the 6 MeV phase–space. [ABSTRACT FROM AUTHOR]

Purpose: An improvement in tissue assignment for low-dose rate brachytherapy (LDRB) patients using more accurate Monte Carlo (MC) dose calculation was accomplished with a metallic artifact reduction (MAR) method specific to dual-energy computed tomography (DECT). Methods: The proposed MAR algorithm followed a four-step procedure. The first step involved applying a weighted blend of both DECT scans (IH/L) to generate a new image (IMix). This action minimized Hounsfield unit (HU) variations surrounding the brachytherapy seeds. In the second step, the mean HU of the prostate in IMix was calculated and shifted toward the mean HU of the two original DECT images (IH/L). The third step involved smoothing the newly shifted IMix and the two original IH/L, followed by a subtraction of both, generating an image that represented the metallic artifact (IA,(H/L)) of reduced noise levels. The final step consisted of subtracting the original IH/L from the newly generated IA,(H/L) and obtaining a final image corrected for metallic artifacts. Following the completion of the algorithm, a DECT stoichiometric method was used to extract the relative electronic density (ρe) and effective atomic number (Zeff) at each voxel of the corrected scans. Tissue assignment could then be determined with these two newly acquired physical parameters. Each voxel was assigned the tissue bearing the closest resemblance in terms of ρe and Zeff, comparing with values from the ICRU 42 database. A MC study was then performed to compare the dosimetric impacts of alternative MAR algorithms. Results: An improvement in tissue assignment was observed with the DECT MAR algorithm, compared to the single-energy computed tomography (SECT) approach. In a phantom study, tissue misassignment was found to reach 0.05% of voxels using the DECT approach, compared with 0.40% using the SECT method. Comparison of the DECT and SECT D90 dose parameter (volume receiving 90% of the dose) indicated that D90 could be underestimated by up to 2.3% using the SECT method. Conclusions: The DECT MAR approach is a simple alternative to reduce metallic artifacts found in LDRB patient scans. Images can be processed quickly and do not require the determination of x-ray spectra. Substantial information on density and atomic number can also be obtained. Furthermore, calcifications within the prostate are detected by the tissue assignment algorithm. This enables more accurate, patient-specific MC dose calculations. [ABSTRACT FROM AUTHOR]

Purpose: Given increasing efforts in biomedical research utilizing molecular imaging methods, development of dedicated high-performance small-animal SPECT systems has been growing rapidly in the last decade. In the present work, we propose and assess an alternative concept for SPECT imaging enabling desktop open-gantry imaging of small animals. Methods: The system, PERSPECT, consists of an imaging desk, with a set of tilted detector and pinhole collimator placed beneath it. The object to be imaged is simply placed on the desk. Monte Carlo (MC) and analytical simulations were utilized to accurately model and evaluate the proposed concept and design. Furthermore, a dedicated image reconstruction algorithm, finite-aperture-based circular projections (FABCP), was developed and validated for the system, enabling more accurate modeling of the system and higher quality reconstructed images. Image quality was quantified as a function of different tilt angles in the acquisition and number of iterations in the reconstruction algorithm. Furthermore, more complex phantoms including Derenzo, Defrise, and mouse whole body were simulated and studied. Results: The sensitivity of the PERSPECT was 207 cps/MBq. It was quantitatively demonstrated that for a tilt angle of 30°, comparable image qualities were obtained in terms of normalized squared error, contrast, uniformity, noise, and spatial resolution measurements, the latter at ~0.6 mm. Furthermore, quantitative analyses demonstrated that 3 iterations of FABCP image reconstruction (16 subsets/iteration) led to optimally reconstructed images. Conclusions: The PERSPECT, using a novel imaging protocol, can achieve comparable image quality performance in comparison with a conventional pinhole SPECT with the same configuration. The dedicated FABCP algorithm, which was developed for reconstruction of data from the PERSPECT system, can produce high quality images for small-animal imaging via accurate modeling of the system as incorporated in the forward- and back-projection steps. Meanwhile, the developed MC model and the analytical simulator of the system can be applied for further studies on development and evaluation of the system. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate various approaches for assessing patient organ doses resulting from radiotherapy cone-beam CT (CBCT), by the use of thermoluminescent dosimeter (TLD) measurements in anthropomorphic phantoms, a Monte Carlo based dose calculation software, and different dose indicators as presently defined. Methods: Dose evaluations were performed on a CBCT Elekta XVI (Elekta, Crawley, UK) for different protocols and anatomical regions. The first part of the study focuses on using PCXMC software (PCXMC 2.0, STUK, Helsinki, Finland) for calculating organ doses, adapting the input parameters to simulate the exposure geometry, and beam dose distribution in an appropriate way. The calculated doses were compared to readouts of TLDs placed in an anthropomorphic Rando phantom. After this validation, the software was used for analyzing organ dose variability associated with patients'differences in size and gender. At the same time, various dose indicators were evaluated: kerma area product (KAP), cumulative air-kerma at the isocenter (Kair), cone-beam dose index, and central cumulative dose. The latter was evaluated in a single phantom and in a stack of three adjacent computed tomography dose index phantoms. Based on the different dose indicators, a set of coefficients was calculated to estimate organ doses for a range of patient morphologies, using their equivalent diameters. Results: Maximum organ doses were about 1 mGy for head and neck and 25 mGy for chest and pelvis protocols. The differences between PCXMC and TLDs doses were generally below 10% for organs within the field of view and approximately 15% for organs at the boundaries of the radiation beam. When considering patient size and gender variability, differences in organ doses up to 40% were observed especially in the pelvic region; for the organs in the thorax, the maximum differences ranged between 20% and 30%. Phantom dose indexes provided better correlation with organ doses than Kair and KAP, with average ratios ranging between 0.9 and 1.1 and variations for different organs and protocols below 20%. The triple phantom setup allowed us to take into account scatter dose contributions, but nonetheless, the correlation with the evaluated organ doses was not improved with this method. Conclusions: The simulation of rotational geometry and of asymmetric beam distribution by means of PCXMC 2.0 enabled us to determine patient organ doses depending on weight, height and gender. Alternatively, the measurement of an in phantom dose indicator combined with proper correction coefficients can be a useful tool for a first dose estimation of in-field organs. The data and coefficients provided in this study can be applied to any patient undergoing a scan by an Elekta XVI equipment. [ABSTRACT FROM AUTHOR]

Purpose: To present and characterize a Monte Carlo (MC) tool for the simulation of the relative biological effectiveness for the induction of direct DNA double strand breaks (RBEdirectDSB ) for protons and light ions. Methods: The MC tool uses a pregenerated event-by-event tracks library of protons and light ions that are overlaid on a cell nucleus model. The cell nucleus model is a cylindrical arrangement of nucleosome structures consisting of 198 DNA base pairs. An algorithm relying on k-dimensional trees and cylindrical symmetries is used to search coincidences of energy deposition sites with volumes corresponding to the sugar-phosphate backbone of the DNA molecule. Strand breaks (SBs) are scored when energy higher than a threshold is reached in these volumes. Based on the number of affected strands, they are categorized into either single strand break (SSB) or double strand break (DSB) lesions. The number of SBs composing each lesion (i.e., its size) is also recorded. RBEdirectDSB is obtained by taking the ratio of DSB yields of a given radiation field to a 60Co field. The MC tool was used to obtain SSB yields, DSB yields, and RBEdirectDSB as a function of linear energy transfer (LET) for protons (1H+), 4He2+, 7Li3+, and 12C6+ ions. Results: For protons, the SSB yields decreased and the DSB yields increased with LET. At ≈24.5 keV μm-1, protons generated 15% more DSBs than 12C6+ ions. The RBEdirectDSB varied between 1.24 and 1.77 for proton fields between 8.5 and 30.2 keV μm- 1, and it was higher for iso-LET ions with lowest atomic number. The SSB and DSB lesion sizes showed significant differences for all radiation fields. Generally, the yields of SSB lesions of sizes ⩾2 and the yields of DSB lesions of sizes ⩾3 increased with LET and increased for iso-LET ions of lower atomic number. On the other hand, the ratios of SSB to DSB lesions of sizes 2-4 did not show variability with LET nor projectile atomic number, suggesting that these metrics are independent of the radiation quality. Finally, a variance of up to 8% in the DSB yields was observed as a function of the particle incidence angle on the cell nucleus. This simulation effect is due to the preferential alignment of ion tracks with the DNA nucleosomes at specific angles. Conclusions: TheMCtool can predict SSB and DSB yields for light ions of various LET and estimate RBEdirectDSB . In addition, it can calculate the frequencies of different DNA lesion sizes, which is of interest in the context of biologically relevant absolute dosimetry of particle beams. [ABSTRACT FROM AUTHOR]

Purpose: To develop a method for estimating doses to primarily exposed organs in pediatric CT by taking into account patient size and automatic tube current modulation (ATCM). Methods: A Monte Carlo CT dosimetry software package, which creates patient-specific voxelized phantoms, accurately simulates CT exposures, and generates dose images depicting the energy imparted on the exposed volume, was used. Routine head, thorax, and abdomen/pelvis CT examinations in 92 pediatric patients, ranging from 1-month to 14-yr-old (49 boys and 43 girls), were simulated on a 64-slice CT scanner. Two sets of simulations were performed in each patient using (i) a fixed tube current (FTC) value over the entire examination length and (ii) the ATCM profile extracted from the DICOM header of the reconstructed images. Normalized to CTDIvol organ dose was derived for all primary irradiated radiosensitive organs. Normalized dose data were correlated to patient's water equivalent diameter using log-transformed linear regression analysis. Results: The maximum percent difference in normalized organ dose between FTC and ATCM acquisitions was 10% for eyes in head, 26% for thymus in thorax, and 76% for kidneys in abdomen/pelvis. In most of the organs, the correlation between dose and water equivalent diameter was significantly improved in ATCM compared to FTC acquisitions (P < 0.001). Conclusions: The proposed method employs size specific CTDIvol-normalized organ dose coefficients for ATCM-activated and FTC acquisitions in pediatric CT. These coefficients are substantially different between ATCM and FTC modes of operation and enable a more accurate assessment of patient-specific organ dose in the clinical setting. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this work is to examine the trade-off between prescription isodose and dose gradients in orthovoltage stereotactic radiosurgery. Methods: Point energy deposition kernels (EDKs) describing photon and electron transport were calculated using Monte Carlo methods. EDKs were generated from 10 to 250 keV, in 10 keV increments. The EDKs were converted to pencil beam kernels and used to calculate dose profiles through isocenter from a 4π isotropic delivery from all angles of circularly collimated beams. Monoenergetic beams and an orthovoltage polyenergetic spectrum were analyzed. The dose gradient index (DGI) is the ratio of the 50% prescription isodose volume to the 100% prescription isodose volume and represents a metric by which dose gradients in stereotactic radiosurgery (SRS) may be evaluated. Results: Using the 4π dose profiles calculated using pencil beam kernels, the relationship between DGI and prescription isodose was examined for circular cones ranging from 4 to 18 mm in diameter and monoenergetic photon beams with energies ranging from 20 to 250 keV. Values were found to exist for prescription isodose that optimize DGI. Conclusions: The relationship between DGI and prescription isodose was found to be dependent on both field size and energy. Examining this trade-off is an important consideration for designing optimal SRS systems. [ABSTRACT FROM AUTHOR]

Optimal dispatch of storage devices is crucial for the economic operation of smart grids with distributed energy resources. Through appropriate scheduling, storage devices can store the energy when the renewable production is high or electricity price is low, and support the demand when electricity is expensive. Conventionally, this scheduling requires a control centre to gather information from the entire system and find the optimal schedule in the required horizon for the controllable devices. This study proposes a fully distributed scheduling methodology based on discrete‐time optimal control, primal‐dual gradient descent, and consensus networks. In the proposed approach, the requirement for the control centre is eliminated and the optimal schedule for all the devices is found solely through iterative coordination of each device with its neighbours. The application of the algorithm is demonstrated in a 5‐bus system and its convergence to the global optimum is validated through Monte Carlo simulations. Further, it is shown that the algorithm is robust against communication link failures provided that the communications topology remains connected or reconnects after being disconnected. [ABSTRACT FROM AUTHOR]