Graphical Optimization Research Articles

Dose optimisation in single plane interstitial brachytherapy

Background and purpose Brachytherapy dose distributions can be optimised by modulation of source dwell times. In this study dose optimisation in single planar interstitial implants was evaluated in order to quantify the potential benefit in patients. Material and methods In 14 patients, treated for recurrent rectal and cervical cancer, flexible catheters were sutured intra-operatively to the tumour bed in areas with compromised surgical margin. Both non-optimised, geometrically and graphically optimised CT -based dose plans were made. The overdose index (OI), homogeneity index (HI), conformal index (COIN), minimum target dose, and high dose volumes were evaluated. The dependence of OI, HI, and COIN on target volume and implant regularity was evaluated. In addition, 12 theoretical implant configurations were analyzed. Results Geometrical and graphical optimisation improved the dose plans significantly with graphical optimisation being superior. Graphically optimised dose plans showed a significant decrease of 18% ± 9% in high dose volume ( p < 0.001). HI, COIN, and OI were significantly improved from 0.50 ± 0.05 to 0.60 ± 0.05, from 0.65 ± 0.04 to 0.71 ± 0.04, and from 0.19 ± 0.03 to 0.15 ± 0.03, respectively ( p < 0.001 for all). Moreover, minimum target dose increased significantly from 71% ± 5% to 80% ± 5% ( p < 0.001). The improvement in OI and HI obtained by optimisation depended on the regularity of the implant, such that the benefit of optimisation was larger for irregular implants. OI and HI correlated strongly with target volume limiting the usability of these parameters for comparison of dose plans between patients. Conclusions Dwell time optimisation significantly improved the dose distribution regarding homogeneity, conformity, minimum target dose, and size of high dose volumes. Graphical optimisation is fast, reproducible and superior to geometric optimisation.

SU‐FF‐T‐141: Comparison Of Inverse Planning Simulated Annealing And Graphical Optimization For Prostate High Dose‐Rate Brachytherapy

Purpose: HDR dose optimization may be performed using a combination of Geometric Optimization (GO) and manual adjustment e.g. Graphical Optimization (GrO), but is time‐consuming. Optimization using anatomy based inverse planning e.g. Inverse Planning with Simulated Annealing (IPSA) can generate a solution in minutes. This study compares optimization using IPSA and GrO for treatment of prostate cancer. Materials and Methods: A retrospective comparison was performed of 63 consecutive patient plans generated and treated using GrO then re‐planned using IPSA. The clinical target volume and critical organs were contoured using PLATO v14.2.6 (Nucletron). A dose of 10Gy per insertion was prescribed to the 100% isodose. Dose optimization was performed using a combination of GO and GrO. For GrO, the isodose was dragged to the desired position, and the system automatically recalculated the appropriate dwell times. For each plan, the following dosimetric comparisons were made between that generated by IPSA and that generated and treated using GrO: prostate V100, V150, V200, urethra V120, Rectal V80, bladder V80, Homogeneity Index (HI) and Conformity Index (COIN). Results: The V100 was slightly lower with IPSA (GrO=97.5%, IPSA=96.7% p=0.001) but with a greater reduction in V150 (GrO=35.6%, IPSA=30.2% p=0.000) and V200 (GrO=12.7%, IPSA=10.7% p=0.000). Similarly, V120 for urethra (GrO=16.1%, IPSA=6.7% p=0.000), V80 for rectum (GrO=2.1%, IPSA=1.3% p=0.000) and V80 for bladder (GrO=2.3%, IPSA=1.3% p=0.000) were significantly lower with IPSA. HI increased (GrO=0.63, IPSA=0.69 p=0.000) while COIN was lower (GrO=0.71, IPSA=0.68 p=0.000). Conclusions: IPSA enables the rapid generation of dose‐optimized plans. The resultant plans provide comparable target coverage but with greater dose homogeneity, a lower high dose volume and lower dose to critical organs. Planning time was reduced using IPSA. This is a significant advantage over other methods of dose optimization in a clinical environment.

Comparison of inverse planning simulated annealing and graphical optimization for prostate high dose-rate brachytherapy

Comparison of inverse planning simulated annealing and graphical optimization for prostate high dose-rate brachytherapy

High-Throughput Screening and Optimization of Photoembossed Relief Structures

A methodology for the rapid design, screening, and optimization of coating systems with surface relief structures, using a combination of statistical experimental design, high-throughput experimentation, data mining, and graphical and mathematical optimization routines was developed. The methodology was applied to photopolymers used in photoembossing applications. A library of 72 films was prepared by dispensing a given amount of sample onto a chemically patterned substrate consisting of hydrophilic areas separated by fluorinated hydrophobic barriers. Film composition and film processing conditions were determined using statistical experimental design. The surface topology of the films was characterized by automated AFM. Subsequently, models explaining the dependence of surface topologies on sample composition and processing parameters were developed and used for screening a virtual 4000-membered in silico library of photopolymer lacquers. Simple graphical optimization or Pareto algorithms were subsequently used to find an ensemble of formulations, which were optimal with respect to a predefined set of properties, such as aspect ratio and shape of the relief structures.

Dosimetric comparison of inverse optimization with geometric optimization in combination with graphical optimization for HDR prostate implants

The purpose of this study is to compare geometric optimization (GO) with anatomy based inverse optimization (ABIO). Five patients of carcinoma prostate treated with HDR interstitial brachytherapy had been studied. Post implant CT scans of 5 mm slice thickness were obtained; target volume and other critical structures rectum, bladder and urethra were drawn by the clinician. Plans were obtained with geometric optimization and anatomy based inversed optimization. Anatomy based inverse planning implemented currently in PLATO BPS version 14.2, is based on geometric and dose point optimization and designed to account for the critical structures. Graphical optimization (GrO) is used to fine-tune the distribution ie to reduce the dose to critical structures and to improve the target coverage in both geometric optimization and anatomy based inverse optimization plans. DVH of target, rectum, bladder and urethra were evaluated and compared, dose homogeneity index and conformity index were also evaluated for all the plans. The mean target coverage was 93.9±7%, 90.3±4%, 82±13%, 91.6±3 for different optimization techniques GO, GO_gr, ABIO and ABIO_gr respectively. The target coverage in ABIO is not clinically acceptable. Maximum dose, dose to 2% of the volume of urethra D2%,U was 137±12%, 123.2±2%, 111.5±9, 122.7±4 for GO, GO_gr, ABIO and ABIO_gr respectively. The mean conformity index values were 0.71, 0.76, 0.65, 0.82 for GO, GO_gr, ABIO, ABIO_gr respectively. ABIO_gr has a good conformity over all other optimization techniques. However the difference is not very significant between GO and GO_gr. The mean values of DHI are 0.81, 0.77, 0.65 and 0.75 for GO, GO_gr, ABIO and ABIO_gr respectively. Geometric optimization is highly homogenous compared to all other optimization techniques.To conclude, target coverage in ABIO is not clinically acceptable. However ABIO followed by graphical optimization is much superior in sparing of critical structures and conformity compared to geometrical optimization. Target coverage is marginally better in GO compared to ABIO_gr. Homogeneity is superior in GO compared to ABIO_gr. However ABIO_gr plans were clinically acceptable with respect to homogeneity. Further, dose escalation to the target is possible with ABIO, without exceeding the tolerance dose to urethra. Clinical correlation of genitourinary toxicity has to be studied.

Review of Introduction to Optimum Design, 2nd Ed. by Jasbir AroraIntroduction to Optimum Design, 2nd Ed.Elsevier Academic Press

Arora’s introduction of a much-anticipated second edition of Introduction to Optimum Design will not only satisfy established users of his well-received first edition, but moreover, significant updates, supplementary material, and fine-tuning of the pedagogical aspects of the presentation will certainly broaden its appeal. For those unfamiliar with the book, Introduction to Optimum Design is one of a number of contemporary works that provide a basic to intermediate introduction to the theory of optimal design with engineering applications. However, among some of the distinguishing characteristics of Arora’s book are its adaptability to audiences with diverse backgrounds, as well as the extent to which it makes the topic clear and approachable. The minimum mathematics prerequisites would include multivariate calculus and some exposure to linear algebra; as such, the book can readily be used with third-year or fourth-year undergraduates in most engineering disciplines. On the other hand, selected topics are treated with sufficient depth and rigor that, when covered at a faster pace, the book is equally well-suited for use at the introductory graduate level. The book would also be excellent as a self-study reference for the practicing engineer. Although perhaps the majority of the applications used in the book are drawn from problems in the civil and mechanical engineering disciplines including a good sampling of structural optimization examples , most examples are framed in such a way that the key concepts can be understood by students from other engineering disciplines. As such, in this reviewer’s personal experience, students from chemical, electrical, and industrial engineering have found the book equally useful. In fact, students from industrial engineering often find the presentation of key mathematical concepts much clearer than what is customarily given in most operations research and quantitative analysis texts. The layout of the first 12 chapters of the second edition consists of: “Introduction to Design,” “Optimum Design Problem Formulation,” “Graphical Optimization,” “Optimum Design Concepts,” “Linear Programming Methods for Optimum Design,” “Numerical Methods for Unconstrained Optimum Design,” “Numerical Methods for Constrained Optimum Design,” and “Introduction to Optimum Design with MATLAB.” Following the basic introduction and description of nomenclature in Chapters 1 and 2, many of the key concepts are introduced for two-variable optimum design problems in Chapter 3 “Graphical Optimization” , which is now an expanded, separate chapter in the revised edition. Improvements in this chapter include examples involving the use of Mathematica and MATLAB for generating graphical solutions. In Chapters 4–11, the basic theoretical and computational aspects of optimization are given in a fashion similar to that of the first edition; however, the key concepts of existence and uniqueness of unconstrained and constrained solutions now Chapters 4 and 5 , umerical methods for linear programming now Chapters 6 and

SU‐FF‐T‐35: Is High‐Dose Rate (HDR) “better Than” and Low‐Dose Rate (LDR) Prostate Brachytherapy? A Dosimetric Study Using Retrospective Data

Purpose: To compare high‐dose rate (HDR) and low‐dose rate (LDR permanent seeds) prostate brachytherapy using dosimetric parameters. Method and Materials: From January 2003 to August 2004, 102 HDR prostate implants were planned on the Nucletron PLATO Brachytherapy with subsequent treatment using Nucletron afterloader (I192 stepping source). During this time period, 72 LDR implants were pre‐planned on Varian Variseed Brachytherapy with subsequent treatment using I125 seeds (a combination of loose and stranded seeds). The HDR implants were forward planned using a combination of manual dwell time adjustments and graphical optimization on patient CT images. The LDR implants were pre‐planned based on ultrasound images and post‐implant dosimetry was assessed at one month from CT. For this study, post‐plans were analyzed using Nucletron PLATO Brachytherapy Seeds. Parameters used for comparison included: Conformal index (COIN), Homogeneity Index (HI), Natural Dose Ratio (NDR) as well as volume and dose coverage indices. Maximum dose contribution to critical structures was reported. Results: Our results show the V100 for HDR with a mean of 96.1% is higher than LDR (post‐plan) with a mean of 81.8% (p&lt;0.001). Conformal Index for HDR was 0.701 compared to LDR pre‐plan (COIN=0.627, p&lt;0.001) and post‐plan (0.534, p&lt;0.001). The homogeneity index showed a significant difference between techniques (HDR HI=0.628, LDR pre‐plan HI=0.518, HI post‐plan HI=0.425). The Natural Dose Ratio did not show a large difference (HDR NDR=1.025, LDR pre‐plan NDR=1.041, LDR post‐plan NDR=0.915). Conclusion: It has been shown high‐dose rate brachytherapy for prostate treatment delivers a more conformal and uniform dose throughout the target than low‐dose rate permanent seeds. The dose contribution to the rectum and urethra is much less with high‐dose rate than low‐dose rate. Dose contribution to the target can be tailored using existing optimization routines and newer algorithms for inverse planning that will make the planning procedure simpler.

TU‐EE‐A1‐03: Comparison of High Dose Rate (HDR) Vs Intensity Modulated Radiation Therapy (IMRT) for Prostate Boost Treatment

Purpose: The objective of this study is to compare dosimetric characteristics of prostate treatments using HDR brachytherapy and IMRT technique. Method and Materials: Five HDR patients were selected for IMRT planning. Patients underwent ultrasound guided catheter placement for HDR. CT images were obtained and imported into the Nucletron PLATO Brachytherapy system. The prostate, urethra, bladder and rectum were contoured on axial slices. The dose was calculated and optimized by graphical optimization. The CT images of these structures were exported from the PLATO to Eclipse workstation for IMRT planning and comparison. For each patient, the DVH of HDR and IMRT plans were generated, drawn on the same scale and compared. Results: In IMRT plans the DVH curves for PTV dropped sharply and reached to zero volume of the prostate at about 6.4 Gy. In HDR plans the DVH curves for PTV showed a long tail up to a very high dose. About 10% of the PTV for prostate received greater than 12 Gy (200%) of the prescribed dose (6 Gy) in HDR plans. In contrast, the same volume in IMRT plans received less than 6 Gy (100%). Average prostate V90 and V100 dose was about 6.3 Gy and 4.12 Gy respectively for HDR, and 6.09 Gy and 5.74 Gy for IMRT plans, respectively. UrethraV90 dose for IMRT plans showed similar levels (93%), whereas in HDR the dose varied widely (60 to 100%). In all plans, the dose to the bladder and rectum was significantly lower in HDR than in IMRT plans. Conclusions: HDR brachytherapy may reduce normal tissue toxicities in prostate boost treatments, even though the dose homogeneity inside the PTV is far worse than in IMRT treatments. Another advantage of HDR over IMRT is that the organ motion is not a significant concern as in IMRT.

Optimizing the laser-welded butt joints of medium carbon steel using RSM

The optimization capabilities in design-expert software were used to optimize the keyhole parameters (i.e. maximize penetration ( P), and minimize the heat input, width of welded zone ( W) and width of heat-affected zone ( W HAZ)) in CW CO 2 laser butt-welding of medium carbon steel. The previous developed mathematical models to predict the keyhole parameters in terms of the process factors, namely laser power (LP), welding speed ( S) and focused position ( F) were used to optimize the welding process. The goal was to set the process factors at optimum values to reach the desirable weld bead quality and to increase the production rate. Numerical and graphical optimization techniques were used. In fact, two optimization criteria were taken into account. In this investigation, optimal solutions were found that would improve the weld quality, increase the productivity and minimize the total operation cost. In addition to that, superimposing the contours for the various response surfaces produced overlay plots.

Optimization of conformal avoidance: A comparative study of prone vs. supine interstitial high-dose-rate breast brachytherapy

Purpose Several recent studies indicate high-dose-rate (HDR) breast brachytherapy as an alternative to standard external beam radiation therapy for partial breast irradiation with high dose conformality to the target. However, this article presents an exploration of the possibility of achieving higher conformal avoidance of sensitive structures through detailed and comparative 3D CT-based anatomical dose distribution of a patient in supine and prone positions. Methods and materials A patient treated with accelerated partial breast HDR breast brachytherapy in the supine position was selected for two CT-based analyses, one in the supine and one in the prone position. The optimized plan (Nucletron HDR planning station) for each position was achieved using graphical optimization with local adjustment of isodose lines to cover the planned target volume (PTV, lumpectomy with 2 cm margin) with 100% of the prescribed dose (34 Gy in 10 fractions) while minimizing the hot spots. Cumulative dose-volume histograms (DVH) were analyzed for the PTV, lung, skin, pectoral muscle, and chest wall. Results The PTV received 100% of prescribed dose in both the prone and supine positions. A significant (>40%) dose reduction was achieved in the lung in the prone treatment position. Similar dose reductions were also achieved for prone pectoral muscle, chest wall, and breast skin, irradiating less volume with high doses. Pectoral muscle, lumpectomy, and the breast skin showed prominent differences in shape and displacement in the prone compared with the supine position. Conclusion CT-based treatment planning allowed calculations of volumetric dose distribution to the target and all sensitive structures with proper visualization and volumetric delineation of organs of interest. The treatment plan shows significant dose reduction may be possible in various sensitive structures if the patient is treated with HDR brachytherapy in the prone position.

Evaluation of Operational Performance of Gas Turbine Cogeneration Plants Using an Optimization Tool: OPS-Operation

To attain the highest performance of gas turbine cogeneration plants, it is necessary to rationally select the numbers and capacities of gas turbines and auxiliary equipment in consideration of their operational strategies corresponding to energy demands which change with season and time. It is also important to rationally select the options such as the variable heat to power by the steam injection or combined cycle, and the inlet air cooling by the ice storage combined with electric compression refrigeration or steam absorption refrigeration. The evaluation of the effects of these alternatives on the performance is an important work for designers. However, it takes much time to conduct the work thoroughly. The authors have developed an optimization tool named “OPS-Operation” to assess the operational strategies for given configurations and specifications of energy supply plants. This tool has a user-friendly interface for the functions of data registration, graphical flowsheet editing, automatic programming and optimization calculation, and graphical representation of results. In this paper, the effects of the aforementioned alternatives on the operational performance of gas turbine cogeneration plants are evaluated using the optimization tool in terms of many criteria including operational cost, energy consumption, and CO2 emission. It is demonstrated that the tool is very effective to evaluate the performance rationally, flexibly, and easily.

Anatomy based inverse planning in HDR prostate brachytherapy

The purpose of this study is to evaluate anatomy based inverse planning as implemented in PLATO BPS 14.2 for planning of HDR prostate implants. Six patients were analysed. The dose distributions were optimized using geometric optimization followed by graphical optimization (GO), anatomy based inverse planning or standard inverse optimization (SIO), tuned inverse optimization (TIO) and tuned inverse optimization followed by graphical optimization (GOTIO). The mean target coverage was 93±4%, 53±11%, 74±8%, 90±3%, respectively, for GO, SIO, TIO and GOTIO. The conformal index COIN was 0.74±0.02, 0.43±0.15 and 0.77±0.07, respectively, for GO, SIO and GOTIO. Improved dose homogeneity was found when comparing GOTIO with GO.

Visualization and User-Modeling for Browsing Personal Photo Libraries

We present a user-centric system for visualization and layout for content-based image retrieval. Image features (visual and/or semantic) are used to display retrievals as thumbnails in a 2-D spatial layout or “configuration” which conveys all pair-wise mutual similarities. A graphical optimization technique is used to provide maximally uncluttered and informative layouts. Moreover, a novel subspace feature weighting technique can be used to modify 2-D layouts in a variety of context-dependent ways. An efficient computational technique for subspace weighting and re-estimation leads to a simple user-modeling framework whereby the system can learn to display query results based on layout examples (or relevance feedback) provided by the user. The resulting retrieval, browsing and visualization can adapt to the user's (time-varying) notions of content, context and preferences in style and interactive navigation. Monte Carlo simulations with machine-generated layouts as well as pilot user studies have demonstrated the ability of this framework to model or “mimic” users, by automatically generating layouts according to their preferences.

Osmotic Dehydration Behavior of Red Paprika (Capsicum Annuum L.)

ABSTRACT: Osmotic dehydration of red paprika was studied using a combined sucrose (5 to 45 g/100 g) and sodium chloride (0 to 15 g/100g) solution. The effective diffusion coefficients for water and solute were determined using the slope method based on the Fickian diffusion model. The effects of concentration of sucrose, sodium chloride and their complex interaction on water and solute diffusion coefficients as well as on equilibrium moisture and solid contents were studied using central composite rotatable design of experiments. The graphical optimization showed that at optimum conditions (sucrose concentration and sodium chloride concentration were 21.86 g/100 g and 2.02 g/100 g, respectively), the following criteria were achieved: water diffusion coefficient (Dew) 0.80 × 10−9 m2/s, solid diffusion coefficient (Des 0.82 × 10−9 m2/s, equilibrium moisture content (m∞) 6.85 kg/kg, and equilibrium solid content (s∞) 2.00 kg/kg.

Concepts and methods in optimization of integrated LC VCOs

Underlying physical mechanisms controlling the noise properties of oscillators are studied. This treatment shows the importance of inductance selection for oscillator noise optimization. A design strategy centered around an inductance selection scheme is executed using a practical graphical optimization method to optimize phase noise subject to design constraints such as power dissipation, tank amplitude, tuning range, startup condition, and diameters of spiral inductors. The optimization technique is demonstrated through a design example, leading to a 2.4-GHz fully integrated, LC voltage-controlled oscillator (VCO) implemented using 0.35-/spl mu/m MOS transistors. The measured phase-noise values are -121, -117, and -115 dBc/Hz at 600-kHz offset from 1.91, 2.03, and 2.60-GHz carriers, respectively. The VCO dissipates 4 mA from a 2.5-V supply voltage. The inversion mode MOSCAP tuning is used to achieve 26% of tuning range. Two figures of merit for performance comparison of various oscillators are introduced and used to compare this work to previously reported results.

A Graphical Approach to Allocating Class Fragments in Distributed Objectbase Systems

This paper contributes by providing an allocation taxonomy to analyze DOBS models and identify the primary characteristics of a DOBS allocation. A graphical optimization technique, based on the work by Kernighan and Lin (The Bell System, Technical Journal, pp. 291–307, 1970), is basis of our approach. The algorithm attempts to arrive at a “near optimal” distribution of fragments by exchanging and/or moving fragments between every pair of sites. The algorithms are implemented and are tested with carefully generated test data to obtain an analysis of the performance. The design, implementation and analysis of the allocation algorithms form the most significant contribution of this paper. Several significant insights are derived from the analysis of the results obtained that can be usefully applied to any real life DOBS allocation design. The applicability of the allocation algorithms for the DOBS model of interest may be verified by a cost benefit analysis based on their efficiency. The optimization of the initial allocation is meaningful only if the improvement obtained by optimization justifies the additional overhead. If significant improvement is not obtainable by optimization then our efficient initial allocation scheme alone may serve the purpose.

High power-added efficiency MMIC amplifier for 2.4 GHz wireless communications

This work describes the design and the measured performance of a high-efficiency monolithic microwave integrated circuit (MMIC) amplifier for wireless communications in the 2.4 GHz band. The monolithic technology employed in the circuit integration is based on standard 0.5-/spl mu/m-gate-length MESFET. The design procedure is based on load-cycle graphic optimization of the transistor performance. On-wafer experimental characterization shows output power up to 24 dBm and excellent results of power-added efficiency up to 79% with 19.5 dBm output power at low drain bias voltage. The amplifier performance achieved and the circuit size, which is 1 mm/sup 2/, are suitable for use in the transmitter chains of wireless communication systems in the 2.4 GHz band.

Economic Design of Biofilter Systems

This paper offers an easy-to-use design model for the minimum net present cost of a biofilter system, allowing for compaction of the bed. It compares the two-variable graphical optimisation approach with short-cut methods having analytical solutions.

Adaptive detection threshold optimization for tracking in clutter

The adaptive optimization of detection thresholds for tracking in clutter is investigated for the probabilistic data association (PDA) filter. Earlier work on this problem by T.E. Fortmann et al. (1985) involved an approximate steady-state analysis of the state error covariance and is only suitable for time-invariant systems. Furthermore, the method requires numerous assumptions and approximations about the error covariance update equation, and uses a cumbersome graphical optimization algorithm. In this work we propose two adaptive schemes for threshold optimization, namely prior and posterior optimization algorithms which minimize the mean-square state estimation error over detection thresholds which depend on data up to the previous and current time-step, respectively. These algorithm are suitable for real-time implementation in time-varying systems. Some simulation results are presented.

ESR measurement of translational diffusion constants

AbstractESR spectroscopy can be used to measure the translational diffusion constants of spin probes in a variety of media using a capillary method. Following preliminary work, it has been possible to improve upon the accuracy of determining diffusion constants in two ways. Both methods require an experimental measurement of the resonant cavity sampling profile. In the first procedure, this cavity profile is convolved with a trial Gaussian distribution and the result is compared with the experimental data obtained from the ESR measurements; the diffusion constant is then determined by graphical optimization. The second method is a graphical one based on a knowledge of the experimental diffusion profile and the cavity sampling profile. Both methods have been shown to give similar results but the second less rigorous corrected‐zero method is generally simpler to apply. For a medium such as water, it takes several days to acquire the necessary experimental data but the time taken to carry out the experiment can be shortened (or slower rates of diffusion can be measured) by using a shielded resonant cavity.