Large Number Of Beams Research Articles

Codebook Design for Vertical Beamforming by Multi-Cell Coordination

Fifth-generation (5G) mobile communication systems employ beamforming technology using massive multiple-input and multiple-output (MIMO) to improve the reception quality and spectrum efficiency within a cell. Meanwhile, coordinated beamforming among multiple base stations is an effective approach to improving the spectrum efficiency at the cell edges, in which massive MIMO is deployed at geographically distant base stations and beamforming control is conducted in a cooperative manner. Codebook-based beamforming is a method for realizing multi-cell coordinated beamforming, in which each base station selects one of multiple beams that are predefined in a codebook. In codebook-based beamforming, it is important to design an efficient codebook that takes into account the beam allocation and the number of beams. In general, the larger the number of beams defined in a codebook, the more finely tuned the beam control can be and a greater improvement in spectrum efficiency can be expected. However, it requires a huge signal processing to optimize the beam combinations with a large number of beams by coordinated beamforming. This paper proposes a novel codebook design that efficiently assigns beam directions and widths in a vertical plane. Computer simulations showed that the proposed codebook performs as well as the conventional method while requiring fewer beam combinations.

Multirow writing method for massively-parallel electron-beam systems

Electron-beam (e-beam) systems with a large number of beams have been developed in order to improve the writing throughput. It is desirable to have a writing method which can control beams to achieve not only a high throughput but also a high quality of writing. In a massively-parallel e-beam system, it is unavoidable that some beams are faulty and the current may vary with the beam. An important issue is how to mitigate the effects of faulty beams and current variation to enhance the quality of a transferred pattern. A possible way to reduce the negative effects of faulty beams is to spread the effects spatially. In this paper, a writing method, referred to as multirow writing, which uses each beam to expose pixels over multiple rows in each writing path, is proposed and the general procedures of realizing the method is described. The multirow writing method minimizes the dose reduction at a pixel and localization of affected pixels without exposing each writing path multiple times.

Avalanche instability of the orbital angular momentum higher order optical vortices

Theoretical and experimental studies of spectra of optical vortices and orbital angular momentum (OAM) carried by combined singular beams are presented. The combined beams are composed of superposition of Laguerre-Gauss or Bessel-Gauss modes with "resonant" amplitudes depending on a real parameter. If the parameter is an integer, then the OAM of the singular beam is equal to this number. If the real parameter is fractional, then the OAM can be either substantially larger or much smaller than the integer closest to the parameter value. For a non-integer value of the beam parameter, a large number of beams from superposition with integer topological charges contribute to its amplitude. For an integer beam parameter, the contribution to the amplitude is made by only one mode with a topological charge equal to the value of the beam parameter. In the experiment, singular beams with fractional OAMs were shaped using a binary amplitude diffraction grating consistent with the phase function of the singular beam. The measured correlation degree between the initial beam and the beam reconstructed from the vortex spectrum was no less than 90%.

Radio Resource Management Optimization of Flexible Satellite Payloads for DVB-S2 Systems

The increasing demand for high-rate broadcast and multicast services over satellite networks has pushed for the development of high throughput satellites characterized by a large number of beams (e.g., more than 100). This, together with the variable distribution of data traffic request across beams and over time, has called for the design of a new generation of satellite payloads, able to flexibly allocate bandwidth and power. In this context, this paper studies the problem of radio resource allocation in the forward link of multibeam satellite networks adopting the digital video broadcasting-satellite-second generation standard. We propose a novel objective function with the aim to meet as close as possible the requested traffic across the beams while taking fairness into account. The resulting non-convex optimization problem is solved using a modified version of the simulated annealing algorithm, for which a detailed complexity analysis is presented. Simulation results obtained under realistic conditions confirm the effectiveness of the proposed approach and shed some light on possible payload design implications.

Fast Inverse Planning of Beam Directions and Weights for Small Animal Radiotherapy

Current preclinical irradiation systems, such as the small animal radiation research platform, provide many capabilities of clinical systems, including on-board cone beam computed tomography (CBCT) imaging, which motivates the development of treatment planning systems. The time for preclinical treatment planning is often limited, however, due to the large number of subjects and the need for anesthesia for imaging and radiation delivery. This paper presents a 3-D inverse planning solution that optimizes beam directions and weights within a timeframe suitable for small animal radiation research. The system begins with a large number of beams and takes advantage of a graphics processing unit-accelerated implementation of the superposition-convolution method to quickly compute the dose for each beam. Optimization is performed by a linear programming solver, with a minimum bound on dose to the target and a maximum bound on dose to organs at risk (OAR). It is extended to dose shells by using hollow cylinders instead of solid beams. The method is demonstrated on mouse CBCT images with arbitrarily defined targets and OAR. Inverse planning is performed in about 5 min, which enables a preclinical workflow that includes CBCT acquisition, treatment planning, and radiation delivery in a single session.

Low-Complexity Beam Allocation for Switched-Beam Based Multiuser Massive MIMO Systems

This paper addresses the beam allocation problem in a switched-beam based massive multiple-input-multiple-output (MIMO) system working at the millimeter wave frequency band, with the target of maximizing the sum data rate. This beam allocation problem can be formulated as a combinatorial optimization problem under two constraints that each user uses at most one beam for its data transmission and each beam serves at most one user. The brute-force search is a straightforward method to solve this optimization problem. However, for a massive MIMO system with a large number of beams $N$ , the brute-force search results in intractable complexity $O(N^{K})$ , where $K$ is the number of users. In this paper, in order to solve the beam allocation problem with affordable complexity, a suboptimal low-complexity beam allocation (LBA) algorithm is developed based on submodular optimization theory, which has been shown to be a powerful tool for solving combinatorial optimization problems. Simulation results show that our proposed LBA algorithm achieves nearly optimal sum data rate with complexity $O(K\log N)$ . Furthermore, the average service ratio, i.e., the ratio of the number of users being served to the total number of users, is theoretically analyzed and derived as an explicit function of the ratio $N/K$ .

Special issue on main results of Call‐off Order 3 (CoO3) in SatNEx III

Special issue on main results of Call‐off Order 3 (<scp>CoO3</scp>) in <scp>SatNEx</scp> III

In reply to the Letter to the Editor titled: “Comments on: Clinical implementation of a new electronic brachytherapy system for skin brachytherapy”

In reply to the Letter to the Editor titled: “Comments on: Clinical implementation of a new electronic brachytherapy system for skin brachytherapy”

A novel implementation of mARC treatment for non-dedicated planning systems using converted IMRT plans

BackgroundThe modulated arc (mARC) technique has recently been introduced by Siemens as an analogue to VMAT treatment. However, up to now only one certified treatment planning system supports mARC planning. We therefore present a conversion algorithm capable of converting IMRT plans created by any treatment planning system into mARC plans, with the hope of expanding the availability of mARC to a larger range of clinical users and researchers. As additional advantages, our implementation offers improved functionality for planning hybrid arcs and provides an equivalent step-and-shoot plan for each mARC plan, which can be used as a back-up concept in institutions where only one linac is equipped with mARC.MethodsWe present a feasibility study to outline a practical implementation of mARC plan conversion using Philips Pinnacle and Prowess Panther. We present examples for three different kinds of prostate and head-and-neck plans, for 6 MV and flattening-filter-free (FFF) 7 MV photon energies, which are dosimetrically verified.ResultsIt is generally more difficult to create good quality IMRT plans in Pinnacle using a large number of beams and few segments. We present different ways of optimization as examples. By careful choosing the beam and segment arrangement and inversion objectives, we achieve plan qualities similar to our usual IMRT plans. The conversion of the plans to mARC format yields functional plans, which can be irradiated without incidences. Absolute dosimetric verification of both the step-and-shoot and mARC plans by point dose measurements showed deviations below 5% local dose, mARC plans deviated from step-and-shoot plans by no more than 1%. The agreement between GafChromic film measurements of planar dose before and after mARC conversion is excellent. The comparison of the 3D dose distribution measured by PTW Octavius 729 2D-Array with the step-and-shoot plans and with the TPS is well above the pass criteria of 90% of the points falling within 5% local dose and 3 mm distance to agreement. For all plans, the treatment time was noticeably reduced by conversion to mARC.ConclusionsWe present the feasibility test for converting IMRT step-and-shoot plans from the RTP-output of any treatment planning system (Philips Pinnacle and Prowess Panther, in our case) into mARC plans. The feasibility and dosimetric equivalence is demonstrated for the examples of a prostate and a head-and-neck patient.

SU-E-T-511: A Dosimetric Comparison Between Superposition Algorithm and Monte Carlo Simulation for SBRT

Purpose: To verify the superposition dose calculation algorithm for SBRT plans using the Monte Carlo simulation and investigate the related issues. Methods: The SBRT plans with 6 MV were originally created on CMS Xio treatment planning system with superposition algorithm. The same patient CT, beam geometry and MUs were used in the Monte Carlo simulation (MC) on MCSIM. MCSIM is an EGS4‐based MC dose calculation system for photon and electron beams. The MC plans were compared with the Xio plans to verify Xio superposition algorithm for SBRT. The electron disequilibrium was particularly investigated by comparing the DVHs for a 2‐mm thick peel of the GTV. The 18‐MV plans and one‐and two‐beam plans were also created for the dosimetric comparison. Results: Five SBRT lung plans created on CMS Xio and delivered on Varian 21 EX linac were included in this study. The tumor GTV ranged from 1.4 cc to 11 cc and the dose ranged from 1950 cGy to 5400 cGy. The comparisons were made in terms of DVHs, mean doses, minimal doses, and maximal doses for GTV. The results showed the mean dose values of the real patient plans agreed with MC to within 3%. However, the differences between Xio and MC were increased to up to 10% for 1‐beam and 2‐beam plans, and the differences were more pronounced for the 18‐MV plans than the 6‐MV plans. Conclusions: The Xio superposition algorithm may not adequately account for electron disequilibrium for one or two beam plans; however, it can perform accurate dose calculation for SBRT with large number of beams. Compared to 18‐MV beams, 6‐MV is preferable as the dose calculation for the 6‐MV plans was more accurate based on the Monte Carlo simulation.

MO‐A‐137‐08: Direct Leaf Trajectory Optimization for Volumetric Modulated Arc Therapy with Sliding Window Delivery

Purpose: We present a new single‐step algorithm for volumetric modulated arc therapy (VMAT) planning. The algorithm is inspired by the observation that IMRT plans with a large number of beams (e.g., N=20) yield near‐optimal treatment plans. However, an arc sequencing step to convert an IMRT plan into a deliverable VMAT plan compromises quality or delivery efficiency. To avoid this caveat, we devise a single‐step method to directly optimize the MLC leaf trajectories. Methods: In our approach, a full 360‐degree arc is divided into N arc segments in which the leaves move unidirectionally, i.e. an intensity‐modulated field is delivered over each arc segment using a sliding window technique. We formulate the VMAT optimization problem in terms of the leaf trajectories over each arc segment, including all machine and time constraints. Assuming constant dose‐influence matrices in each arc segment and constant gantry speed, this optimization problem is convex. Thus, we can reliably determine the optimal VMAT plan under these restrictions. An extension of this basic model is devised that accounts for a varying dose influence matrix within each arc segment. Results: The algorithm allows us to find highly conformal treatment plans, deliverable in a short time. Allowing for enough delivery time, the algorithm is guaranteed to match the ideal IMRT plan. For prostate cases, the plans are observed to closely approximate the ideal plan with 3–4 minutes delivery time. Head‐and‐neck results are similarly promising. Conclusion: The results indicate that high quality single‐arc treatments can be delivered with 20 arc segments if sufficient time is allowed for modulation in each segment. Our current implementation is customized towards finding optimal VMAT plans for constant gantry speed and dose rate, which is desirable in practice. In the future, the model can be extended to allow variable dose rate and more general leaf trajectories. Research supported by Philips Radiation Oncology Systems.

TH-A-116-08: Guaranteed Epsilon-Optimal Treatment Plans with Minimum Number of Beams for Stereotactic Body Radiation Therapy

Purpose: To efficiently find quality‐guaranteed treatment plans with the minimum number of beams for stereotactic body radiation therapy (SBRT). Methods: We formulate the beam angle optimization problem (BAO) as a mixed integer programming problem (MIP) whose solution gives the optimal beam orientation as well as optimal beam intensity. We first allow use of all candidate beams and find the ' 'ideal plan' ' with the objective of minimizing dose to organs at risk (OARs) while keeping the dose to the tumor and other structures in specified ranges. Then we resolve the MIP with the objective of minimizing the number of beams while remaining in a predetermined epsilon‐optimality of the ideal plan with respect to the dose to OARs. Since the treatment plan optimization is a multicriteria optimization problem, the planner can navigate the ideal dose distribution Pareto surface and select a plan of desired target coverage versus OARs sparing, and then use the proposed technique to reduce the number of beams while guaranteeing epsilon‐optimality. To reduce the computation time, we use a family of heuristic cuts, known as ((neighbor cuts)) while preserving epsilon‐optimality. For the numerical experiments a liver case with 34 and a lung case with 36 coplanar beams were considered. Results: The ideal plan uses an impractically large number of beams. The proposed technique reduced the number of beams to the range of practical application (5 to 9 beams) while remaining in the epsilon‐optimal range of 1% to 5% optimality gap. Adding the neighbor cuts reduced the computation time considerably. Conclusion: The proposed method can be integrated into a general algorithm for fast navigation of the ideal dose distribution Pareto surface and finding the treatment plan with the minimum number of beams, which corresponds to the delivery time, in epsilon‐optimality range of the desired ideal plan. The project was supported by the Federal Share of program income earned by Massachusetts; General Hospital on C06 CA059267, Proton Therapy Research and Treatment Center and also partially by RaySearch laboratories.

Analytic study on the effects of the number of MLC segments and the least segment area on step-and-shoot head-and-neck IMRT planning using direct machine parameter optimization

In this study, we present the concurrent effects of the number of segments (NS) and the least segment area (LSA) for step-and-shoot head-and-neck intensity-modulated radiation therapy (IMRT) planning using the direct machine parameter optimization (DMPO), on which basis we suggest the optimal NS and LSA ranges. We selected three head-and-neck patients who had received IMRT via the simultaneous integrated boost (SIB) technique and classified them as easy, intermediate, and difficult cases. We formulated a benchmark plan and made 11 additional plans by re-optimizing the benchmark by varying the NS and the LSA for each case. Clinical and physical plan-quality evaluation parameters were considered separately: the conformality index (CI), the homogeneity index (HI) and the maximum or mean doses for the organs-at-risk were the clinical factors, and these were summarized as plan-quality parameter, Q. The modulation index (MI), the total monitor units (MUs), and the final composite cost function F were employed as parameters in the evaluation of the physical aspects. A 2-way analysis of variance (2-way ANOVA) was used to determine the effects of the NS and the LSA concurrently. Pearson’s correlations among the total MU, MI, F, and Q were examined as well. Overall plan-efficiency factor ɛ was defined to estimate the optimal NS and LSA by considering the plan’s quality and the beam delivery efficiency together. Plans with simple targets or a small number of beams (NB) were affected by the LSA whereas plans with complex targets or large NB were affected by the NS. Moreover, smaller NS and smaller LSA were advantageous for simple plans whereas larger NS and smaller LSA were beneficial for complex plans. When we consider the plan’s quality and the beam delivery efficiency, {NS = 60–80, LSA = 8–12 cm2} are the proper ranges for head-and-neck IMRT planning with DMPO; however, the combination may differ based on the complexity of a given plan.

Modeling of Very Large Interacting Multiple-Beam Systems with Application to Suspension Bridge Cables

Systems of parallel beams connected with springs appear often in engineering. Typical examples are bundles of wires, such as the ones appearing in suspension bridge cables. These connections result in coupling of the differential equations describing the problem. In this paper, two systems of parallel beams connected with springs perpendicular to the beams are examined: multiple beams connected with springs, and multiple beams of common stiffness connected with springs and subjected to a common tensile axial load. A method is proposed to decouple the system of coupled equations into uncoupled differential equations for which exact shape functions can be constructed, so that the computational effort associated with systems involving a very large number of beams can become manageable. Numerical examples are presented demonstrating the capabilities of the proposed method.

Sensitivity analysis for accurate determination of PSF parameters

One possible candidate to address future nodes (below 16nm) is electron beam lithography as sub 10nm resolution was already demonstrated in PMMA or HSQ resists. If multiple electron beam systems significantly increase the throughput to meet industrial needs, it can be the tool of choice. Nevertheless using a chemically amplified resist (CAR) is mandatory even for systems with a large number of beams. Achieving dense sub 20nm patterns with CAR is still a challenge as proximity effects degrade the contrast of the aerial image. Bridging, shape rounding or partial development are typical degradation in the desired final pattern shape. Proximity effect correction is needed in order to properly delineate dense features as well as meet the required CD uniformity. Proximity effect correction can only be accurate if a Point Spread Functions (PSF) is precisely determined. In this paper we demonstrate a strategy that allows accurate determination of Point Spread Function parameters. This strategy consists in using sensitivity analysis in order to define conditions where the calibration features and the measured quantities are sensitive enough to the PSF parameters and this without a correlation between the final results.

Application of the constrained finite strip method for the buckling design of cold-formed steel columns and beams via the direct strength method

This paper discusses the effect of rounded corners in the capacity prediction of cold-formed steel members. Three important aspects are identified and investigated by performing parametric numerical studies on a large number of beams and columns of various cross-sections. Calculations have been performed by using sharp and rounded corners, and by using the conventional and the constrained finite strip method. On the basis of the results a simple and unambiguous method is proposed for the capacity prediction which requires sharp-cornered cross-sections only. The proposal is validated by comparison to test data.

Computational enhancements to fluence map optimization for total marrow irradiation using IMRT

The fluence map optimization (FMO) problem is a core problem in intensity modulated radiation therapy (IMRT) treatment planning. Although it has been studied extensively for site-specific treatment planning, few studies have examined efficient computational methods for solving it for intensity modulated total marrow irradiation (IM-TMI) planning; few studies have also looked at exploiting prior beamlet information to solve the FMO problem in a beam orientation optimization context. In this study, we consider different types of line search strategies and different types of warm-start techniques to improve the speed with which the FMO problem for IM-TMI is solved and the quality of the end solution. We also consider a parallelism-enhanced algorithm to solve the FMO problem for IM-TMI treatment planning with a large number of beams (36 equispaced beams at each of 11 isocenters, for a total of 396 beams). We show that the backtracking line search strategy with step reduction exhibits the best performance and that using either of the two types of warm-start techniques which we consider leads to significant improvements in both solution time and quality. We also provide results for the aforementioned 396-beam plan and show that 30-beam solutions obtained using beam orientation optimization attain a comparable level of quality as this larger solution.

Symmetry tuning for ignition capsules via the symcap technique

Symmetry of an implosion is crucial to get ignition successfully. Several methods of control and measurement of symmetry have been applied on many laser systems with mm size hohlraums and ns pulses. On the National Ignition Facility [Moses et al., Phys. Plasmas 16, 041006 (2009)] we have large hohlraums of cm scale, long drive pulses of 10 s of ns, and a large number of beams with the option to tune their wavelengths. Here we discuss how we used the x-ray self-emission from imploding surrogates to ignition capsules (symcaps) to measure the symmetry of the implosion. We show that symcaps are good surrogates for low order symmetry, though having lower sensitivity to distortions than ignition capsules. We demonstrate the ability to transfer energy between laser beams in a gas-filled hohlraum using wavelength tuning, successfully tuning the lowest order symmetry of the symcaps in different size hohlraums at different laser energies within the specification established by calculations for successful ignition.

Pre-Perforated Post-Reinforced Structural Panels of Baked Clay as Cheaper Alternative of RCC Construction

The lack of resources in third world countries and unaffordability of modern materials of construction including RCC by common man has led of the use of local materials by employing technical approach for construction of houses without sacrificing the strength and durability at relatively lower cost than reinforced concrete. Therefore systematic research has been initiated to test the strength and other structural properties of pre-perforated post-reinforced baked clay beams of clay which have been compacted through compression to verify its suitability as major material of construction. A large number of beams have been tested and it is quite possible that this would serve as major material of construction in the areas where the soil is alluvial in nature and the cost of transportation of material is substantially higher and would render the RCC construction uneconomical. To start with twenty five sites were selected at different locations and basic material properties such as compressive strength, tensile strength, poisson's ratio and modulus of elasticity were determined after baking at uniform temperature and by applying reasonable compression for compaction. The effect in terms of natural salts and alkalinity were studied in order to find the best possible ratio in terms of clay, silt, pit-sand and other impurities. Here a number of beams were tested without shear reinforcement. The results did not differ drastically from those of RCC and therefore it holds promise for further research to be carried out.

A miniature high resolution 3-D imaging sonar

This paper discusses the design and development of a miniature, high resolution 3-D imaging sonar. The design utilizes frequency steered phased arrays (FSPA) technology. FSPAs present a small, low-power solution to the problem of underwater imaging sonars. The technology provides a method to build sonars with a large number of beams without the proportional power, circuitry and processing complexity. The design differs from previous methods in that the array elements are manufactured from a monolithic material. With this technique the arrays are flat and considerably smaller element dimensions are achievable which allows for higher frequency ranges and smaller array sizes. In the current frequency range, the demonstrated array has ultra high image resolution (1″ range × 1° azimuth × 1° elevation) and small size (<3″ × 3″). The design of the FSPA utilizes the phasing-induced frequency-dependent directionality of a linear phased array to produce multiple beams in a forward sector. The FSPA requires only two hardware channels per array and can be arranged in single and multiple array configurations that deliver wide sector 2-D images. 3-D images can be obtained by scanning the array in a direction perpendicular to the 2-D image field and applying suitable image processing to the multiple scanned 2-D images. This paper introduces the 3-D FSPA concept, theory and design methodology. Finally, results from a prototype array are presented and discussed.