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Results for “Optimization”

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PubMed1998

An evaluation of the factors influencing selection of the optimal size of laryngeal mask airway in normal adults.

The purpose of this randomised single blinded study was to determine the optimal size of laryngeal mask airway in the normal adult population, to test the validity of the current selection criteria and to determine if any externally measured anatomical variable correlated with optimal size. In each of 30 apnoeic anaesthetised adults weighting less than 100 kg, size 3, 4 and 5 laryngeal mask airways were inserted in random order by a skilled user and the cuff inflated to a standard pressure (60 cm H2O). Optimal size was based on four criteria in order of priority: number of attempts at placement, oropharyngeal leak pressure, fiberoptic score and percentage of vocal cords seen. The size 5 laryngeal mask airway was optimal in 19/30 and the size 4 in 11/30. In no patient was the size 3 the optimal fit. Oropharyngeal leak pressure was significantly higher for each progressively large size and the fiberoptic view was significantly better for the size 4 and size 5. There was no significant predictive value in any externally measured anatomical variable, but height was the most useful. The best current selection strategy was to choose a size 5 for males and size 4 for females. Potentially useful new strategies may be to use the size 5 in all adults, or a size 5 > or = 165 cm in height and size 4 for < 165 cm. We conclude that predicting the optimal size of laryngeal mask airway for individual adult patients is complex. The best size selection strategies involve use of the size 4 and 5 laryngeal mask airways in adults.

Adolescent↗

PubMed2003

Statistical optimization of a high maltose-forming, hyperthermostable and Ca2+-independent alpha-amylase production by an extreme thermophile Geobacillus thermoleovorans using response surface methodology.

AIM: Statistical optimization for maximum production of a hyperthermostable, Ca2+-independent and high maltose-forming alpha-amylase by Geobacillus thermoleovorans. METHODS AND RESULTS: G. thermoleovorans was cultivated in 250 ml flasks containing 50 ml of chemically defined glucose-arginine medium (g l(-1): glucose 20; arginine 1.2; riboflavin 150 microg ml(-1); MgSO4. 7H2O 0.2; NaCl 1.0; pH 7.0). The medium was inoculated with 5 h-old bacterial inoculum (1.8x10(8) CFU ml(-1)), and incubated in an incubator shaker at 70 degrees C for 12 h at 200 rev min(-1). The fermentation variables optimized by 'one variable at a time' approach were further optimized by response surface methodology (RSM). The statistical model was obtained using central composite design (CCD) with three variables: glucose, riboflavin and inoculum density. An over all 24 and 70% increase in enzyme production was attained in shake flasks and fermenter because of optimization by RSM, respectively. A good coverage of interactions could also be explained by RSM. The end products of the action of alpha-amylase on starch were maltose (62%), maltotriose (31%) and malto-oligosaccharides (7%). CONCLUSIONS: RSM allowed optimization of medium components and cultural parameters for attaining high yields of alpha-amylase, and further, a good coverage of interactions could be explained. The yield of maltose was higher than maltotriose and malto-oligosaccharides in the starch hydrolysate. SIGNIFICANCE AND IMPACT OF THE STUDY: By applying RSM, critical fermentation variables were optimized rapidly. The starch hydrolysate contained a high proportion of maltose, and therefore, the enzyme can find application in starch saccharification process for the manufacture of high maltose syrups. The use of this enzyme in starch saccharification eliminates the addition of Ca2+.

Analysis of Variance↗

PubMed2002

Hand size influences optimal grip span in women but not in men.

This study investigates which position (grip span) on the standard grip dynamometer results in maximum grip strength. Our null hypotheses included (1) no optimal grip span exists for measuring grip strength and (2) optimal grip span is unrelated to hand size. We also intended to derive a simple mathematical algorithm to adapt grip span to hand size. Seventy healthy subjects (40 women/30 men; mean age, 40 years; range; 20-80 years) free of upper-limb lesions were evaluated. Each hand was randomly tested on 10 occasions using 5 different grip spans. Our findings showed that (1) optimal grip span was identified for both genders and (2) hand size and optimal grip span correlated in women but not in men. When measuring handgrip strength in women, hand size must be taken into consideration. We provide a mathematical equation (y = x/5 + 1.5 cm) to adapt optimal grip span (y) to hand size (x) in women. In adult men, optimal grip span can be set at a fixed value (5.5 cm).

Adult↗

PubMed2001

Optimal electrocardiographic leads for detecting acute myocardial ischemia.

This study identifies the most sensitive electrocardiographic leads for monitoring ST-segment changes caused by acute coronary ischemia. The data set consisted of 120-lead electrocardiograms (ECGs) digitally recorded during balloon-inflation angioplasty in 3 groups of patients with single-vessel disease (left anterior descending [LAD], 32; right coronary artery [RCA], 36; left circumflex [LCx], 23). The ST deviation was measured in all recorded leads during baseline and ischemic states, and its difference between these 2 states (DeltaST) was calculated at 352 sites and plotted as DeltaST maps. The patients in each group were divided, by means of DeltaST criteria, into subgroups of "responders" and "nonresponders." Mean DeltaSTs for each group/subgroup were calculated and standardized by the corresponding standard deviation (SD); these values were plotted as mean DeltaST and t maps. Sites where extrema of DeltaST occurred most frequently were sought in bootstrap trials, performed in each group/subgroup. The results suggest that the optimal sites for the ischemia-sensitive leads are: V(3) (+) and just below V(8) (-) for LAD-related ischemia; the left iliac crest (+) and above V(3) at the third intercostal space (-) for RCA-related ischemia; and just below V(8) (+) and above V(2) at the third intercostal space (-) for LCx-related ischemia. Three "optimal" bipolar leads using these sites registered, in the responders from the LAD, RCA, and LCx groups, mean DeltaST (+/-SD) of 232 +/- 59, 245 +/- 96 and 158 +/- 91 microV, respectively; the corresponding t values were 15.14, 9.90, and 6.75. In the 12-lead ECG, only lead V(3) approached optimal DeltaST and t values for the LAD responders (187 +/- 61 microV; t = 11.75) and lead III for the RCA responders (191 +/- 76 microV; t = 9.73), but even these values were significantly suboptimal (P = 0.0011 and P = 0.0120, respectively). We found that the "optimal" bipolar leads can be derived, to an excellent approximation, from the 12 standard leads or from 3 EASI leads (with 3 electrodes at Frank's transverse level and 1 on the manubrium), by using precalculated regression coefficients. By means of bootstrap trials, we estimated the mean sensitivity (SE) and the mean positive predictive value (PPV) with which 3 "optimal" vessel-specific leads could identify ischemia related to the LAD, RCA, and LCx arteries, in the test set, as (SE/PPV) 94.7/92.8%, 78.7/80.9%, and 81.5/80.9%. A similar diagnostic performance can be achieved by vessel-specific leads derived from the 12-lead ECG (93.0/93.4%, 76.6/82.0%, and 82.7/77.1%) and, interestingly, from the EASI lead system (97.8/88.4%, 78.0/80.2%, and 76.8/83.2%). Thus, although the "optimal" bipolar leads for detecting ischemia related to each of the 3 coronary arteries were found to require sampling outside the 12-lead ECG, these leads can be derived from the full set of 12 standard leads or--for clinical monitoring applications--from the EASI lead system by using fewer electrodes at convenient locations.

Acute Disease↗

PubMed2001

[Measurement of CSF flow in the spinal canal using MRI with an optimized MRI protocol: experimental and clinical studies].

PURPOSE: Measurement of the oscillating CSF flow in the spinal canal (SC) of healthy volunteers and in patients with post-traumatic syringomyelia (PTS) using an optimized MRI protocol as well as to determine whether stenosis induced velocity changes are detectable using MRI. METHODS: In 68 healthy volunteers quantitative studies of CSF flow in the cervical, thoracic, and lumbar regions were performed. First, an optimized sequence was developed and tested in 19 volunteers using four different flow-encoding velocities (4, 8, 12, 16 cm/s). Secondly, the optimized sequence was employed in 49 volunteers to measure the different CSF patterns in the cervical, thoracic, and lumbar spinal canals (CSC, TSC, LSC). Part three of the study, in which patients with PTS are being examined is still underway. We measured the maximum velocity (cm/s), the pixel area (mm2), and the stroke volume (ml/s). Using a flow model the velocities prior to and after compression with 5 different power levels were measured at the stenosis and at a distance of 70 cm. RESULTS: A total of 226 dynamic measurements have been performed--so far 76 in the first part (62 = 81.5% evaluable) and 150 in the second part--using the optimized sequence and optimal flow velocities. A flow-encoding sequence of 12 cm/s was found best in the CSC and one of 6 cm/s in the TSC and LSC. The maximum velocity in the CSC was 0.95 cm/s with the flow being directed caudal and 0.38 cm/s with the flow being directed cranial. In the TSC the values were 4.7 cm/s and 1.65 cm/s and in the LSC 0.96 cm/s and 0.59 cm/s. The highest velocities were found at the TSC, which has the smallest diameter compared to the CSC and LSC. In the 4 patients with PTS, the maximum velocities were between 0.09 cm/s and 0.97 cm/s with the flow being directed cranial and between 0.04 cm/s and 1.03 cm/s with the flow being directed caudal. The stroke volumina in the CSC were between 0.1 and 1.23 ml/s (mean: 0.48 ml/s) and 0.2 and 2.45 ml/s (mean: 0.66 ml/s) in the TSC and in the LSC 0.08 ml/s and 0.67 ml/s (mean: 0.29 ml/s). The results of the flow model studies showed an increase of velocity between 2.06 and 4.94 cm/s (mean: 3.31 cm/s) at the stenosis and 1.1 and 1.33 cm/s (mean: 1.23 cm/s) at a distance of 70 cm. CONCLUSION: Quantitative measurement of the oscillating CSF flow in the entire spinal canal (SC) is possible using an optimized MRI protocol as well as to detect stenosis induced velocity changes. Due to the high interindividual variability in the data of spinal CSF dynamics, further studies are necessary to collect normal data. The detection of movement of CSF in a post-traumatic spinal cord lesion may alter the therapeutic management.

Adult↗

PubMed2003

A rational approach for selection of optimal covariate-based dosing strategies.

BACKGROUND: At present, there is no rational approach for choosing a dosing strategy for individualization based on a covariate. An approach to use in establishment of an a priori dosing strategy for individualization is presented. Factors influencing the choice of such a dosing strategy are identified. METHODS: The approach requires definition of the following: target variable, seriousness of deviations from the target (ie, risk function), population model, covariate distributions, and constraints. Minimizing the total risk yields an optimal dosing strategy, estimated as dose sizes for different subpopulations and covariate cutoff values at which doses are increased or decreased. The method was illustrated with the use of simulated and real drug examples for the situation in which clearance is related to creatinine clearance. RESULTS: The estimated optimal cutoff(s) paralleled the median creatinine clearance in the population. The extent of variability in clearance explained by creatinine clearance was the main factor influencing the optimal ratios between adjacent dose sizes. An optimal dosing strategy was possible to estimate for the real drug. CONCLUSIONS: The method is simple to perform, although one difficulty lies in defining the target variable and risk function. Our results imply that commonly used constraints in dosing strategies based on renal function (ie, dose ratio of 2 and predetermined cutoffs) are nonoptimal in the sense we propose. Because an optimal dosing strategy may not be practical to use, the therapeutic cost that would result with any constraint can be assessed by comparison of the outcome after the desired and the optimal strategy.

Creatinine↗

PubMed2004

Shape insensitive optimal adhesion of nanoscale fibrillar structures.

Gecko and many insects have adopted nanoscale fibrillar structures on their feet as adhesion devices. Here, we consider adhesion between a single fiber and a substrate by van der Waals or electrostatic interactions. For a given contact area A, the theoretical pull-off force of the fiber is sigma(th)A where sigma(th) is the theoretical strength of adhesion. We show that it is possible to design an optimal shape of the tip of the fiber to achieve the theoretical pull-off force. However, such design tends to be unreliable at the macroscopic scale because the pull-off force is sensitive to small variations in the tip shape. We find that a robust design of shape-insensitive optimal adhesion becomes possible only when the diameter of the fiber is reduced to length scales on the order of 100 nm. In general, optimal adhesion could be achieved by a combination of size reduction and shape optimization. The smaller the size, the less important the shape. At large contact sizes, optimal adhesion could still be achieved if the shape can be manufactured to a sufficiently high precision. The robust design of optimal adhesion at nanoscale provides a plausible explanation for the convergent evolution of hairy attachment systems in biology.

Animal Structures↗

PubMed2007

Improved evolutionary optimization from genetically adaptive multimethod search.

In the last few decades, evolutionary algorithms have emerged as a revolutionary approach for solving search and optimization problems involving multiple conflicting objectives. Beyond their ability to search intractably large spaces for multiple solutions, these algorithms are able to maintain a diverse population of solutions and exploit similarities of solutions by recombination. However, existing theory and numerical experiments have demonstrated that it is impossible to develop a single algorithm for population evolution that is always efficient for a diverse set of optimization problems. Here we show that significant improvements in the efficiency of evolutionary search can be achieved by running multiple optimization algorithms simultaneously using new concepts of global information sharing and genetically adaptive offspring creation. We call this approach a multialgorithm, genetically adaptive multiobjective, or AMALGAM, method, to evoke the image of a procedure that merges the strengths of different optimization algorithms. Benchmark results using a set of well known multiobjective test problems show that AMALGAM approaches a factor of 10 improvement over current optimization algorithms for the more complex, higher dimensional problems. The AMALGAM method provides new opportunities for solving previously intractable optimization problems.

Algorithms↗

PubMedDate not supplied

Stability and change in optimism: a study among spouse caregivers.

The extent to which caregivers (N = 30) for spouses with probable Alzheimer's disease show lability in optimism was explored. The relationship between caregivers' level of state optimism and level of affect was examined as well. The caregivers completed a measure of optimism and affect every day for 30 consecutive days. They showed variability in optimism over time, and their state optimism could be differentiated from their affect. In addition, we found individual differences in lead-lag relationships between optimism and affect over time. The results section clearly shows that most individuals did not show lead-lag relationships. These findings are integrated into the literature on caregiving.

Affect↗

PubMed2002

Non-microscopic method for malaria diagnosis using OptiMAL IT, a second-generation dipstick for malaria pLDH antigen detection.

Rapid diagnostic tests for malaria are now a commonly used procedure for malaria diagnosis. New or improved devices need to be evaluated against a recognised gold-standard procedure and subjected to conditions of temperature and humidity that may affect their performance. The OptiMAL 48 RDT has now been available commercially for several years and a second-generation OptiMAL IT test is now coming onto the market. In this study the problems associated with the routine use of OptiMAL 48 is investigated and its performance compared with a second-generation individual test, OptiMAL IT. Sensitivity and specificity for detection of all malaria species for both tests were comparable but loss of sensitivity of the test strips due to humidity or temperature found with the routine use of OptiMAL 48 was not seen with the individual OptiMAL IT. False-positive results for Plasmodium falciparum, seen in two negative blood samples, were attributed to the presence of high levels of heterophile antibodies.

Animals↗

PubMed2001

Malaria diagnosis and treatment under the strategy of the integrated management of childhood illness (IMCI): relevance of laboratory support from the rapid immunochromatographic tests of ICT Malaria P.f/P.v and OptiMal.

The algorithm developed for the integrated management of childhood illness (IMCI) provides guidelines for the treatment of paediatric malaria. In areas where malaria is endemic, for example, the IMCI strategy may indicate that children who present with fever, a recent history of fever and/or pallor should receive antimalarial chemotherapy. In many holo-endemic areas, it is unclear whether laboratory tests to confirm that such signs are the result of malaria would be very relevant or useful. Children from a holo-endemic region of Tanzania were therefore checked for malarial parasites by microscopy and by using two rapid immunochromatographic tests (RIT) for the diagnosis of malaria (ICT Malaria P.f/P.v and OptiMal. At the time they were tested, each of these children had been targeted for antimalarial treatment (following the IMCI strategy) because of fever and/or pallor. Only 70% of the 395 children classified to receive antimalarial drugs by the IMCI algorithm had malarial parasitaemias (68.4% had Plasmodium falciparum trophozoites, 1.3% only P. falciparum gametocytes, 0.3% P. ovale and 0.3% P. malariae). As indicators of P. falciparum trophozoites in the peripheral blood, fever had a sensitivity of 93.0% and a specificity of 15.5% whereas pallor had a sensitivity of 72.2% and a specificity of 50.8%. The RIT both had very high corresponding sensitivities (of 100.0% for the ICT and 94.0% for OptiMal) but the specificity of the ICT (74.0%) was significantly lower than that for OptiMal (100.0%). Fever and pallor were significantly associated with the P. falciparum asexual parasitaemias that equalled or exceeded the threshold intensity (2000/microl) that has the optimum sensitivity and specificity for the definition of a malarial episode. Diagnostic likelihood ratios (DLR) showed that a positive result in the OptiMal test (DLR = infinity) was a better indication of malaria than a positive result in the ICT (DLR = 3.85). In fact, OptiMal had diagnostic reliability (0.93) which approached that of an ideal test and, since it only detects live parasites, OptiMal is superior to the ICT in monitoring therapeutic responses. Although the RIT may seem attractive for use in primary health facilities because relatively inexperienced staff can perform them, the high cost of these tests is prohibitive. In holo-endemic areas, use of RIT or microscopical examination of bloodsmears may only be relevant when malaria needs to be excluded as a cause of illness (e.g. prior to treatment with toxic or expensive drugs, or during malaria epidemics). Wherever the effective drugs for the first-line treatment of malaria are cheap (e.g. chloroquine and Fansidar), treatment based on clinical diagnosis alone should prove cost-saving in health facilities without microscopy.

Algorithms↗

PubMed2006

Parent driver characteristics associated with sub-optimal restraint of child passengers.

OBJECTIVES: To identify parent driver demographic and socioeconomic characteristics associated with the use of sub-optimal restraints for child passengers under nine years. METHODS: Cross-sectional study using in-depth, validated telephone interviews with parent drivers in a probability sample of 3,818 vehicle crashes involving 5,146 children. Sub-optimal restraint was defined as use of forward-facing child safety seats for infants under one or weighing under 20 lbs, and any seat-belt use for children under 9. RESULTS: Sub-optimal restraint was more common among children under one and between four and eight years than among children aged one to three years (18%, 65%, and 5%, respectively). For children under nine, independent risk factors for sub-optimal restraint were: non-Hispanic black parent drivers (with non-Hispanic white parents as reference, adjusted relative risk, adjusted RR = 1.24, 95% CI: 1.09-1.41); less educated parents (with college graduate or above as reference: high school, adjusted RR = 1.27, 95% CI: 1.12-1.44; less than high school graduate, adjusted RR = 1.36, 95% CI: 1.13-1.63); and lower family income (with $50,000 or more as reference: <$20,000, adjusted RR = 1.23, 95% CI: 1.07-1.40). Multivariate analysis revealed the following independent risk factors for sub-optimal restraint among four-to-eight-year-olds: older parent age, limited education, black race, and income below $20,000. CONCLUSIONS: Parents with low educational levels or of non-Hispanic black background may require additional anticipatory guidance regarding child passenger safety. The importance of poverty in predicting sub-optimal restraint underscores the importance of child restraint and booster seat disbursement and education programs, potentially through Medicaid.

Accidents, Traffic↗

PubMed2001

Application of a mixed optimization strategy in the design of a pharmaceutical solid formulation at laboratory scale.

The objective of this work was to develop an optimization strategy for the design of pharmaceutical formulations. The mixed strategy was used to optimize a dry powder blend containing 500mg of alpha methlyl dopa to be filled into hard gelatin capsules. The experimental plan consisted of assessing blend flow and dissolution rate using formulations manufactured at small laboratory scale, selecting the optimum formulation, and confirming the data. Two optimization techniques were used in the solid pharmaceutical product design: a genetic algorithm (GA) and a downhill simplex technique. The genetic algorithm used in this work was implemented in an interactive form. Data for each generation of formulations were introduced to the computer with the corresponding values of a fitness function, which was determined in experimental form for each individual formulation. The fitness function used to evaluate product performance (capsule) was defined in terms of the dissolution rate multiplied by a weight function that penalizes those formulations with flow index outside a predefined range. The formulation design contained variable concentrations and types of lubricants/ glidants. There were 64 combinations of seven agents with discrete ranges of concentrations codified into a 16-bit chromosome. Crossing and mutation operations were implemented with relatively high probabilities, for generations with a relatively small number of individuals, due to the restrictions imposed by the experimental cost. The mixed formulation strategy based on genetic algorithms and downhill simplex was used to obtain sequentially improved formulations based on two desired targets: in vitro dissolution rate and flow properties. The basic downhill simplex method was used to obtain an optimal, formulation on the regression response surface obtained from the genetic algorithm data. The results obtained in this work clearliy illustrate the potential of the proposed mixed optimization strategy to obtain optimal formulations.

Algorithms↗

PubMed2004

Application of a mixture experimental design in the optimization of a self-emulsifying formulation with a high drug load.

Response surface methodology (RSM) was applied to optimize the self-emulsifying drug delivery system (SEDDS) containing 25% (w/w) Drug A, a model drug with a high lipophilicity and low water solubility. The key objective of this study was to identify an optimal SEDDS formulation that: 1) possesses a minimum concentration of the surfactant and a maximum concentration of lipid and 2) generates a fine emulsion and eliminates large size droplets (> or = 1 microm) upon dilution with an aqueous medium. Three ingredient variables [PEG 400, Cremophor EL, and a mixture of glycerol dioleate (GDO), and glycerol monooleate (GMO)] were included in the experimental design, while keeping the other ingredients at a fixed level (25% Drug A, 6% ethanol, 3% propylene glycol, 4% water, and 2% tromethamine) in the SEDDS formulation. Dispersion performance of these formulations upon dilution with a simulated gastrointestinal fluid was measured, and the population of the large droplets was used as the primary response for statistical modeling. The results of this mixture study revealed significant interactions among the three ingredients, and their individual levels in the formulation collectively dictated the dispersion performance. The fitted response surface model predicted an optimal region of the SEDDS formulation compositions that generate fine emulsions and essentially eliminates large droplets upon dilution. The predicted optimal 25% Drug A-SEDDS formulations with the levels of Cremophor EL ranging from 40-44%, GDO/GMO ranging from 10-13%, and PEG 400 ranging from 2.7-9.0% were selected and prepared. The dispersion experiment results confirmed the prediction of this model and identified potential optimal formulations for further development. This work demonstrates that RSM is an efficient approach for optimization of the SEDDS formulation.

Algorithms↗

PubMed1990

The derivation and verification of a non-stationary, optimal smoothing filter for nuclear medicine image data.

A non-stationary optimal smoothing filter for digital nuclear medicine image data, degraded by Poisson noise, has been derived and applied to temporal simulated and clinical gated blood pool study (GBPS) data. The derived filter is automatically calculated from a large group (library) of similar GBPS which are representative of all studies acquired according to the same protocol in a defined patient population (the ensemble). The filter is designed to minimize the mean-square difference between the filtered data and the true image values; it provides an optimal trade-off between noise reduction and signal degradation for members of the ensemble. The filter is evaluated using a computer simulated ensemble of GBPS. Libraries of Poisson-degraded and non-degraded studies were generated. Libraries of up to 400 Poisson-degraded simulated studies were used to estimate optimal temporal filters that, when applied to Poisson-degraded members of the ensemble not included in the libraries, reduced the mean-square error in the raw data by 65%. When the non-degraded studies were used instead to compute the optimal filter values, the corresponding reduction in the error was 83%. Libraries of previously acquired clinical GBPS were then used to estimate optimal temporal filters for an ensemble of similarly acquired studies. These filters were subsequently applied to studies of 13 patients (not in the original libraries) who received multiple sequential repeat studies. Comparisons of both the filtered and raw data to averages of the repeat studies demonstrated that optimal filters calculated from 400 and 800 clinical studies reduced the mean-square error in the clinical data by 56% and 63% respectively.

Filtration↗

PubMed2003

Global convergence analysis of fast multiobjective gradient-based dose optimization algorithms for high-dose-rate brachytherapy.

We consider the problem of the global convergence of gradient-based optimization algorithms for interstitial high-dose-rate (HDR) brachytherapy dose optimization using variance-based objectives. Possible local minima could lead to only sub-optimal solutions. We perform a configuration space analysis using a representative set of the entire non-dominated solution space. A set of three prostate implants is used in this study. We compare the results obtained by conjugate gradient algorithms, two variable metric algorithms and fast-simulated annealing. For the variable metric algorithm BFGS from numerical recipes, large fluctuations are observed. The limited memory L-BFGS algorithm and the conjugate gradient algorithm FRPR are globally convergent. Local minima or degenerate states are not observed. We study the possibility of obtaining a representative set of non-dominated solutions using optimal solution rearrangement and a warm start mechanism. For the surface and volume dose variance and their derivatives, a method is proposed which significantly reduces the number of required operations. The optimization time, ignoring a preprocessing step, is independent of the number of sampling points in the planning target volume. Multiobjective dose optimization in HDR brachytherapy using L-BFGS and a new modified computation method for the objectives and derivatives has been accelerated, depending on the number of sampling points, by a factor in the range 10-100.

Algorithms↗

PubMed2004

A dose calculation method including scatter for IMRT optimization.

IMRT optimization is an iterative process in which many dose calculations may be necessary. A fast and accurate dose calculation engine is essential for the optimization program to converge to a reliable solution in a reasonable time. Previously we developed a fast dose calculation method for IMRT optimization based on the table lookup (TLP). The TLP kernel is constructed from the dose distributions computed from an accurate superposition/convolution (SC) algorithm at the beginning. Dose calculations at subsequent iterations are performed by looking up the kernel in memory, therefore are very fast. However, it is assumed by the TLP that the beamlet only deposits doses to the voxels on its path. In this paper, we propose an improved table lookup based dose calculation method that includes the scatter contribution (TLPS). The intensity map for each beam is decomposed into an even and an odd checkbox-type pattern for the construction of the kernel for primary and scatter components. The performance of this algorithm is compared with the methods of SC only and TLP without scatter on a few clinical cases and the advantages of speed and accuracy are demonstrated. This method is especially useful for those optimizations that utilize the IMRT optimization as an inner loop, such as the beam angle optimization.

Algorithms↗

PubMed2006

Fast multifield optimization of the biological effect in ion therapy.

In this paper, we present a new technique for simultaneous multifield optimization of the biological effect (i.e. relative biological effectiveness times dose) for intensity modulated radiotherapy with ion beams. It offers complete inverse treatment planning by taking into account planning constraints for the target volume as well as for organs at risk. The approach is based on the mixed irradiation formalism of the linear-quadratic model from radiobiology. We employ a novel objective function to directly optimize the biological effect rather than the physical dose. The required biological input data are reduced to a minimum and are completely independent from the optimization itself. They can be derived from any radiobiological model or even from directly measured data. The new optimization method was fully integrated into our inverse treatment planning tool KonRad. Comparisons with the TRiP98 treatment planning code were done for simple spread-out Bragg peaks as well as for three-dimensional treatment plans, where all fields were optimized separately. While the agreement between both planning systems was very good, the calculation time was substantially reduced in KonRad. By enabling the multifield optimization, the quality of the treatment plans and the sparing of healthy tissues can be clearly improved.

Algorithms↗