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ABSTRACT: Purpose: The effectiveness of IMPT may be significantly diminished by range and patient setup uncertainties. The purpose of this presentation is to evaluate the ability of robust optimization methods to desensitize H&N IMPT plans to uncertainties and their impact on plan optimality. Methods: We use a robust optimization method, in which the objective function value for a given iteration is computed using the 'worst case' dose distribution. The conventionally optimized PTV-based IMPT plans and robustly optimized plans were generated for 14 head and neck cancer cases. The dose standard deviation was calculated for every voxel and used to compute 'standard-deviation volume histograms' (SVHs). The area under SVH curves was used to quantify the plan robustness. In addition, D1cc doses for spinal cord and brainstem, mean doses Dmean for oral cavity and parotids, and D1% doses for other organs were used to assess plan optimality. D5% and D95% doses are used to assess target dose coverage and homogeneity. The plan optimality and robustness are then compared statistically by the pair t-tests using SPSS 19.0 software. Results: Compared with PTV-based optimization, robust optimization provides significantly more robust dose distribution for both targets and organs without sacrificing, and possibly even improving, the sparing of normal tissues. In addition, our robust optimization method also leads to more homogeneous dose distribution in targets with better prescription dose coverage. Improvements are statistically significant with p-value smaller than 0.05 for almost all end points compared. Conclusion: Robust optimization results in patient-specific, optimizer-determined, and effectively reduced margins compared to a predefined and fixed margin used in the PTV approach. The optimizer can find a desired beamlet weight solution from the degenerate solution space so that the dose distribution follows the changes in anatomical geometry and is minimally perturbed by uncertainties. Our results demonstrate the importance of robust optimization. This research is supported by National Cancer Institute (NCI) grant P01CA021239, the University Cancer Foundation via the Institutional Research Grant program at the University of Texas MD Anderson Cancer Center, and MD Andersona^™s cancer center support grant CA0 16672.
Medical Physics 06/2012; 39(6):3835. · 2.83 Impact Factor
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ABSTRACT: Purpose: While intensity-modulated proton therapy (IMPT) has great potential to deliver highly conformal tumoricidal dose to targets whilst minimizing dose to nearby organs-at-risk, IMPT optimization is very time consuming and memory extensive due to finer dose grids and a large number of energy layers used compared to intensity-modulated radiation therapy (IMRT). In this presentation, for the first time, a new approach is introduced to speed up the IMPT treatment planning through application of parallel computing with Graphic Processor Units (GPUs). Methods: Parallel computation with GPUs, which are affordable and can be plugged in a workstation easily, is potentially a good way to improve the computation efficiency. In our approach, we used the standard quadratic objective function to optimize the intensity map of beamlets. The objective function and gradient equations, which are the most time consuming parts of the optimization, were calculated with GPUs. We compared the computation time of optimization done by an Intel ® Core™ i7 CPU and that by the same CPU accelerated by GPUs (TESLA C1060). The influence matrix was pre- calculated before optimization with an in-house proton pencil beam dose calculation engine. Two clinical cases were studied: one base-of-skull (BOS) case (clivus chordoma) and one prostate case (adenocarcinoma). The dose volume histogram (DVH) data for the tumor and critical organs were derived for comparison of optimization results generated by CPU and GPUs. Results: For the BOS case, application of GPUs for the optimization and overall gained 54 and 36.5 times speedup. For the prostate case, application of GPUs for the optimization and overall gained 69 and 28.5 times speedup. Conclusions: The application of GPUs for the parallel computing of IMPT treatment plan optimization can dramatically improve the computation efficiency. The optimization time can be reduced from typically half to one hour to only several minutes.
Medical Physics 06/2012; 39(6):3964-3965. · 2.83 Impact Factor
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ABSTRACT: Purpose: Proton dose distributions, IMPT in particular, are highly sensitive to setup and range uncertainties. We report a novel method, based on per-voxel standard deviation (SD) of dose distributions, to evaluate the robustness of proton plans and to robustly optimize IMPT plans to render them less sensitive to uncertainties. Methods: For each optimization iteration, nine dose distributions are computed - the nominal one, and one each for ± setup uncertainties along x, y and z axes and for ± range uncertainty. SD of dose in each voxel is used to create SD-volume histogram (SVH) for each structure. SVH may be considered a quantitative representation of the robustness of the dose distribution. For optimization, the desired robustness may be specified in terms of an SD-volume (SV) constraint on the CTV and incorporated as a term in the objective function. Results of optimization with and without this constraint were compared in terms of plan optimality and robustness using the so called'worst case' dose distributions; which are obtained by assigning the lowest among the nine doses to each voxel in the clinical target volume (CTV) and the highest to normal tissue voxels outside the CTV. The SVH curve and the area under it for each structure were used as quantitative measures of robustness. Penalty parameter of SV constraint may be varied to control the tradeoff between robustness and plan optimality. We applied these methods to one case each of H&N and lung. Results: In both cases, we found that imposing SV constraint improved plan robustness but at the cost of normal tissue sparing. Conclusions: SVH-based optimization and evaluation is an effective tool for robustness evaluation and robust optimization of IMPT plans. Studies need to be conducted to test the methods for larger cohorts of patients and for other sites. This research is supported by National Cancer Institute (NCI) grant P01CA021239, the University Cancer Foundation via the Institutional Research Grant program at the University of Texas MD Anderson Cancer Center, and MD Andersona^™s cancer center support grant CA016672.
Medical Physics 06/2012; 39(6):3850. · 2.83 Impact Factor
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ABSTRACT: Purpose: Robust optimization leads to IMPT plans that are more robust than and superior in optimality compared to PTV-based optimized plans. Robust optimization incorporates setup and range uncertainties, which implicitly adds margins to targets and organs-at-risk (OARs); whereas PTV-based optimization only considers setup uncertainties and adds margins only to targets in practice. The purpose of this work is to determine if the superiority of robustly optimized plans is due to not assigning margins to OARs during PTV-based optimization. Methods: Plan robustness and optimality of the PTV plus Planning organs-at-Risk Volume (PRVs)-based plans and robustly optimized plans were compared for 5 head and neck cancer cases and one rhabdomyosarcoma case. The PRVs were generated by expansion from OARs by 3 mm. 9 different dose distributions were computed - one each for ± setup uncertainties along three spatial directions, for ± range uncertainty, and the nominal dose distribution. The worst-case dose distribution was obtained by assigning the lowest dose among the 9 doses to each voxel in the target and the highest dose to each voxel outside the target. The DVHs from the worst-case dose were used to assess the plan optimality and robustness. D1cc doses for spinal cord and brainstem, mean doses Dmean for oral cavity and parotids, and D1% doses for other organs were also used to assess plan optimality. D5% and D95% doses are used to assess target dose coverage and homogeneity. Results: For H&N cases, PTV+PRV-based optimization was inferior to robust optimization. However, PTV+PRV-based optimization yielded plans that spared OARs better than PTV-based optimization, although the target dose robustness and homogeneity were comparable to the PTV-based optimization. The same conclusions are also valid in the rhabdomyosarcoma case. Conclusions: We find that the PTV+PRV method can partly improve plan optimality, but it is still inferior to robust optimization method. This research is supported by National Cancer Institute (NCI) grant P01CA021239, the University Cancer Foundation via the Institutional Research Grant program at the University of Texas MD Anderson Cancer Center, and MD Andersona^™s cancer center support grant CA016672.
Medical Physics 06/2012; 39(6):3849-3850. · 2.83 Impact Factor
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ABSTRACT: Purpose: Intensity-modulated proton therapy (IMPT) using multi-field optimization (MFO) could generate highly conformal dose distributions but it is more sensitive to setup and proton range uncertainties than IMPT using single-field optimization (SFO). This work evaluates the effectiveness of SFO treatment plans with the use of energy absorbers (EAs) to improve the robustness and delivery efficiency of IMPT for head and neck cancers. Methods: IMPT treatment plans were generated using 2-field SFO with an EA in each field (EA-SFO) for four patients with head and neck cancers. We compared the plan quality, robustness, and delivery efficiency of the EA- SFO plan with a 3-field MFO plan that was used to treat the patient. Robustness analysis of each plan was performed to generate two dose distributions, consisting of the highest and the lowest possible doses from spatial and range perturbations at every voxel. Dosimetric indices and the numbers of energy layers required in the EA-SFO and MFO plans were compared. Results: All the nominal EA-SFO plans are clinically acceptable. They achieved similar levels of target coverage compared to the MFO plans; the differences in D95 of the GTV and CTVs between the two plans were within 3.5%. Although some of the OARs received higher dose in the EA- SFO plan, they were all within tolerance. The EA-SFO plans yielded an average of 38.5% reduction of plan sensitivity to uncertainties in the targets and 18.5% overall. The EA-SFO plans used an average of 79 (46%) fewer energy layers than the MFO plans, which corresponds to nearly 3 minutes shorter delivery time. Conclusions: The use of energy absorber greatly facilitated the design of clinically acceptable SFO treatment plans. Compared to MFO, EA-SFO not only improved the robustness to setup and range uncertainties, but also reduced the time required for delivery and patient QA.
Medical Physics 06/2012; 39(6):3965. · 2.83 Impact Factor
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ABSTRACT: ZrO2-based composites with WC addition can be successfully machined by electrical discharge machining (EDM) in demineralised water.
ZrO2 composites with 40vol.% WC were produced from nanocrystalline and micrometre sized WC starting powders in order to compare
their tribological behaviour. Friction and wear data are obtained on wire-EDM’ed ZrO2–WC composite flats sliding against a WC–Co cemented carbide pin using a small-scale pin-on-plate testing rig. Correlations
between wear volume, wear rate and friction coefficient on the one hand and material properties and test conditions on the
other hand were elucidated. The experimental results revealed that the grain size of the electro-conductive WC-phase exhibits
a strong influence on the friction and wear behaviour of the ZrO2-based composite.
Tribology Letters 04/2012; 30(3):191-198. · 1.58 Impact Factor
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ABSTRACT: Endovascular treatment of complex, wide-necked bifurcation cerebral aneurysms is challenging. Intra/extra-aneurysmal stent placement, the "waffle cone" technique, has the advantage of using a single stent to prevent coil herniation without the need to deliver the stent to the efferent vessel. The published data on the use of this technique is limited. We present our initial and follow-up experience with the waffle cone stent-assisted coiling (SAC) of aneurysms to evaluate the durability of the technique. We retrospectively identified ten consecutive patients who underwent SAC of an aneurysm using the waffle cone technique from July 2009 to March 2011. Clinical and angiographic outcomes after initial treatment and follow-up were evaluated. Raymond Class I or II occlusion of the aneurysm was achieved in all cases with the waffle cone technique. No intraoperative aneurysm rupture was noted. The parent arteries were patent at procedure completion. Clinical follow-up in nine patients (median 12.9 months) revealed no aneurysm rupture. Two patients had a transient embolic ischemic attack at 18 hours and three months after treatment, respectively. Catheter angiography or MRA at six-month follow-up demonstrated persistent occlusions of aneurysms in seven out of eight patients. Another patient had stable aneurysm occlusion at three-month follow-up study. Our experience in the small series suggests the waffle cone technique could be performed on complex, wide-necked aneurysms with relative safety, and it allowed satisfactory occlusions of the aneurysms at six months in most cases.
Interventional Neuroradiology 03/2012; 18(1):20-8. · 0.56 Impact Factor
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ABSTRACT: Recently, quasi-periodic, rapidly propagating waves have been observed in extreme ultraviolet by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) instrument in about 10 flare/coronal mass ejection (CME) events thus far. A typical example is the 2010 August 1 C3.2 flare/CME event that exhibited arc-shaped wave trains propagating in an active region (AR) magnetic funnel with ~5% intensity variations at speeds in the range of 1000-2000 km s–1. The fast temporal cadence and high sensitivity of AIA enabled the detection of these waves. We identify them as fast magnetosonic waves driven quasi-periodically at the base of the flaring region and develop a three-dimensional MHD model of the event. For the initial state we utilize the dipole magnetic field to model the AR and include gravitationally stratified density at coronal temperature. At the coronal base of the AR, we excite the fast magnetosonic wave by periodic velocity pulsations in the photospheric plane confined to a funnel of magnetic field lines. The excited fast magnetosonic waves have similar amplitude, wavelength, and propagation speeds as the observed wave trains. Based on the simulation results, we discuss the possible excitation mechanism of the waves, their dynamical properties, and the use of the observations for coronal MHD seismology.
The Astrophysical Journal Letters 09/2011; 740(2):L33. · 5.53 Impact Factor
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ABSTRACT: A dielectric–mechanical coupled finite element formulation from partial differential equations is derived, and the formulation is implemented in the framework of FEAP (Taylor 2008 FEAP—A Finite Element Analysis Program, Version 8.2 User Manual University of California at Berkeley). For the enhancement of the calculation efficiency in the three-dimensional simulation, a partitioned solution scheme is utilized, and time integration is implemented explicitly for the mechanical part. A comparison of the numerical results in two- and three-dimensional Lamb wave propagations is performed, and the formation of the Lamb waves and the tangential stress distribution imposed on the aluminum plate by a lead–zirconate–titanate (PZT) patch are investigated. A virtual Lamb wave phased array comprised of 16 PZT patches is developed by tuning the symmetric mode of the Lamb wave to be dominant. The 16 PZT patches are excited individually, aiming at a point, and the numerical result shows good agreement as regards the estimated times of arrival and the focused response at the target point.
Smart Materials and Structures 06/2010; 19(8):085002. · 2.09 Impact Factor
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ABSTRACT: A novel approach to position and orientation estimation for vision-based UAV (unmanned aerial vehicle) navigation is described. In this approach the position and orientation estimation problem is formulated as a tracking problem and solved by using an extended Kalman filter (EKF). The state and observation models of the EKF are established based on an analysis of the imaging geometry of the UAV's video camera in connection with a DEM (digital elevation map) of the area of flight, which helps to control estimation error accumulation. The efficacy of our approach is demonstrated by simulation experiment results.
IEEE Transactions on Aerospace and Electronic Systems 05/2010; · 1.10 Impact Factor
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ABSTRACT: From comparative dry sliding pin-on-plate experiments on distinctive WC-Co and WC-Ni cemented carbides, machined by grinding
or wire-EDM, correlations are derived between wear rate, wear volume and coefficient of friction on the one hand and contact
load, sliding distance, microstructure and surface finish condition on the other hand. The EDM induced surface modification
turns out to deteriorate wear resistance, especially during the wear-in stage of sliding. These findings are in agreement
with X-ray diffraction measurements of the residual stress level in the WC phase.
KeywordsDry sliding-cemented carbide-Tribology-wire-EDM
12/2009: pages 435-436;
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ABSTRACT: A theoretical model has been set up to investigate analytically the effective anisotropy field of the single-phase and anisotropic nanostructured ferromagnetic materials with uniaxial magnetocrystalline anisotropy. It is revealed that the effective anisotropy field decreases with the grain alignment by the increased deviation of the magnetization from the easy-axis in the transition region and the enhanced suppressing effect of the intergrain exchange coupling on the anisotropy. It is suggested that magnetic properties such as the soft magnetic properties could be improved by controlling the crystallographic orientation and the intergrain or interlayer exchange coupling. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 04/2009; 246(7):1709 - 1715. · 1.32 Impact Factor
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ABSTRACT: Structure and magnetic properties of mechanically alloyed Cu-doped Sm Co <sub>6.7-x</sub> Cu <sub>x</sub> Cr <sub>0.3</sub> (x=0.1–0.7) magnets have been systematically studied. The magnetically hard main phase is found to be of Th <sub>2</sub> Ni <sub>17</sub> type in the Sm Co <sub>6.7-x</sub> Cu <sub>x</sub> Cr <sub>0.3</sub> alloys. A small amount of Cu addition is favorable for the formation of the 2:17 phase/Co nanocomposite structure in the alloys. The increase of Cu doping results in more Cu precipitating in the alloys with separating the grains, which significantly enhances the intrinsic coercivity <sub>i</sub>H<sub>c</sub> of the alloys and weakens the exchange coupling between the magnetically hard and soft phases. The magnetization reversal processes of the magnets have been discussed, upon the measurement of the recoil curves.
Journal of Applied Physics 12/2007; · 2.17 Impact Factor
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ABSTRACT: Heavy quark drag coefficients due to three-body elastic scattering in a quark–gluon plasma have been evaluated in the lowest order in QCD. They are found to have similar values as those due to two-body elastic scattering, and both are larger than those due to two-body radiative scattering if the momenta of charm and bottom quarks are below about 4 and 9 GeV/c, respectively. Including three-body elastic scattering increases the momentum degradation of heavy quarks in QGP, bringing the nuclear modification factor for electrons from the decays of produced heavy mesons in Au+Au collisions at closer to the measured one.
Journal of Physics G Nuclear and Particle Physics 07/2007; 34(8):S775. · 4.18 Impact Factor
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ABSTRACT: In order to optimize the structure of a CPL evaporator and enhance heat transfer, a mathematical and physical model is developed
to analyze the flow and heat transfer in the porous wick of the evaporator, whose calculation domain is divided into two parts:
vapor-saturated region and liquid-saturated region. The characteristics of flow and heat transfer in the porous wick of a
CPL evaporator have been numerically studied according to the field synergy principle. The influences of geometrical structures
and heat flux on heat transfer enhancement are analyzed and illustrated by the figures in the present paper.
Heat and Mass Transfer 01/2007; 43(12):1273-1281. · 0.90 Impact Factor
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ABSTRACT: We have demonstrated a simple and universal morphology-controlled growth of
2D ordered Fe/SiO2 magnetic nanodots array, which was based on 2D
colloidal monolayer template composed of polystyrene (PS) spheres and
one-step sol-gel spin-coating technique. The Fe/SiO2 nanodots have a
well-ordered structure arranged in a hexagonal pattern. The dots have the
shape of quasi-pyramidal tetrahedron, which reside in the interstitial
region between three PS spheres and the substrate. Magnetic measurements
reveal that the nanodots array exhibits the in-plane easy magnetization
direction. Compared with the unpatterned Fe/SiO2 thin film, the dots
array has lower saturated field, higher remanence and coercivity. The
present method is applicable to 2D ordered nanodots array of other magnetic
materials.
Physics of Condensed Matter 05/2006; 51(4):501-506. · 1.53 Impact Factor
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ABSTRACT: The icosahedral phase was observed to coexist with a CsCl-type τ-phase in melt-spun AlCuFe alloys in a rather large composition range. A definite orientation relationship between these two phases was determined by electron diffraction and can be discussed from the viewpoint of the formation of a semicoherent interface with good interplanar match.In schmelzgesponnenen AlCuFe-Legierungen kann die ikosaedrische Phase mit einer τ-Phase des CsCl-Typs in einem großen Konzentrationsbereich koexistieren. Zwischen diesen beiden Phasen wird eine Orientierungsbeziehung mittels Elektronenbeugung festgestellt, die zur Ausbildung einer semikohärenten Grenzfläche führt.
physica status solidi (a) 04/2006; 124(1):75 - 80. · 1.21 Impact Factor
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ABSTRACT: An efficient two-dimensional (2-D) analytical and numerical procedure has been proposed to investigate three-dimensional (3-D) internal flows through a passage with a spatially variable depth, in which the viscous forces act significantly on both upper and lower walls. The integral 2-D version of the Navier–Stokes equation was obtained by integrating the full Navier–Stokes equation in a 3-D form over the depth of the passage. In order to examine the validity of the integrated momentum equations, fully-developed flows in straight noncircular ducts were investigated analytically prior to numerical investigations. It has been shown that the exact solutions for circular, elliptical and equilateral triangular ducts are obtainable from the integrated Navier–Stokes equation. Having confirmed its wide applicability to internal flows, numerical computations were conducted to investigate the oscillation mechanism of a fluidic oscillator. Comparison of the present prediction and experiment reveals the validity of the present treatment.
International Journal of Computational Fluid Dynamics. 02/2006; 20(2):99-104.
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ABSTRACT: A quantitative model is described and verified to predict the growth of oil droplets by coalescence on a single nanofiber. The model considers a stream of fluid carrying many tiny droplets of a different fluid. The mechanisms by which the tiny droplets are captured by a drop growing on a fiber are considered. Different capture mechanisms are examined, including interception, Brownian motion of droplets, and vapor deposition by diffusion. It is shown that droplet interception and Brownian diffusion contribute to drop growth on nanofibers for airborne oil droplets in the size range from 100 to 1000 nm. Merging of growing drops on the fiber is also modeled and experimentally observed. © 2005 American Institute of Chemical Engineers AIChE J, 2006
AIChE Journal 09/2005; 52(1):217 - 227. · 2.26 Impact Factor
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ABSTRACT: In this study, FeNi3/Al2O3 core-shell
nanocomposites, where individual FeNi3 nanoparticles were coated with a
thin layer of alumina, were fabricated by a modified sol-gel method. Several physical characterizations were performed on the samples of FeNi3/Al2O3 nanocomposites with different thickness of Al2O3 shell. The encapsulation of FeNi3 nanoparticles with
alumina stops FeNi3 agglomeration during heat treatment, and prevents
interaction among the closely spaced magnetic FeNi3 nanoparticles. The
Al2O3 insulating shell improves the soft magnetic properties of FeNi3. The study of the complex permeability of the samples shows that the real part μ’ of the permeability of the sample with Al molar content of 20% (Al/(Fe+Ni)) is as high as 12, and independent of frequency up to at least 1 GHz. The tunneling magnetoresistance arising from the presence of the Al2O3 shell have also been studied.
Physics of Condensed Matter 07/2005; 46(4):471-474. · 1.53 Impact Factor
