bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Streamline Curvature Throughflow Method for Radial Turbomachinery
Authors: Casey Michael , Robinson Chris
Published: April 2010

This paper describes a newly developed streamline curvature throughflow method for the analysis of radial or mixed flow machines. The code includes curved walls, curved leading and trailing edges, and internal blade row calculating stations. A general method of specifying the empirical data provides separate treatment of blockage, losses, and deviation. Incompressible and compressible fluids are allowed, including real gases and supersonic relative flow in blade rows. The paper describes some new aspects of the code. In particular, a relatively simple numerical model for spanwise mixing is derived; the calculation method for prescribed pressure ratio in compressor blade rows is described; and the method used to redistribute the flow across the span due to choking is given. Examples are given of the use and validation of the code for many types of radial turbomachinery, and these show that it is an excellent tool for preliminary design.
Approximate Elasticity Solution for Orthotopic Cylinder Under Hydrostatic Pressure and Band Loads
Authors: Misovec A. P. , Kempner J.
Published: April 2010

An approximate solution to the Navier equations of the three-dimensional theory of elasticity for an axisymmetric orthotopic circular cylinder subjected to internal and external pressure, axial loads, and closely spaced periodic radial loads is developed. Numerical comparison with the exact solution for the special case of a transversely isotropic cylinder subjected to periodic band loads shows that very good accuracy is obtainable. When the results of the approximate solution are compared with previously obtained results of a Flu¨gge-type shell solution of a ring-reinforced orthotropic cylinder, it is found that the shell theory gives fairly accurate representations of the deformations and stresses except in the neighborhood of discontinuous loads. The addition of transverse shear deformations does not improve the accuracy of the shell solution.
Response of an Elastic Half Space to Uniformly Moving Circular Surface Load
Authors: Singh S. K. , Kuo J. T.
Published: April 2010

The problem of a uniformly moving circular surface load of a general orientation on an elastic half space for two types of load distribution, viz., “uniform” and “hemispherical,” is considered. The solutions have been obtained in integral form. The displacements on the surface of the half space, in the case in which the load velocity V is smaller than the transverse wave velocity of the medium CT are expressed in a closed form as a sum of two terms by using properties of Gauss’ hypergeometric functions. One of these terms gives the static part of the solution, whereas the other term represents the velocity effect part. At distances greater than about five radii from the center of the moving circular load, a moving point load is found to be a good approximation.
A Numerical Solution of Three-Dimensional Problems in Dynamic Elasticity
Authors: Recker W. W.
Published: April 2010

The equations governing the dynamic deformation of an elastic solid are considered as a symmetric hyperbolic system of linear first-order partial-differential equations. The characteristic properties of the system are determined and a numerical method for obtaining the solution of mixed initial and boundary-value problems in elastodynamics is presented. The method, based on approximate integral relations along bicharacteristics, is an extension of the method proposed by Clifton for plane problems in dynamic elasticity and provides a system of difference equations, with second-order accuracy, for the explicit determination of the solution. Application of the method to a problem which has a known solution provides numerical evidence of the convergence and stability of the method.
Mechanical Properties of Anisotropic Fiber-Reinforced Composites
Authors: Chen C. H. , Cheng Shun
Published: April 2010

This paper presents an analytical determination of the elastic constants of composite materials with transversely isotropic elastic circular fiber inclusions in terms of the elastic moduli and the geometric parameters of the constituents. Hexagonal array fiber arrangement is assumed. The problem is solved within the framework of linear elasticity theories of isotropic and anisotropic elastic bodies by subjecting the composite to uniform normal and shearing strain fields. Solutions are obtained in series forms and the Fourier method and the least-square method are used. Numerical results are compared with existing analysis and experiments.
Stresses in Redundant Mechanisms
Authors: Beggs J. S.
Published: April 2010

The methods of classical kinematics and of structures are combined to determine the internal loads acting on the members of a statically indeterminant mechanism. The effect of manufacturing tolerances on stresses is investigated. For example, end play in a crank bearing caused the bending stress in a connecting rod to increase by a factor of 13.7 for the same input.
Stability of Linear Systems With Parametric Excitation
Authors: Dickerson J. R.
Published: April 2010

A Lyapunov-type approach is used to develop sufficient asymptotic stability conditions for linear systems with time-varying coefficients. In particular, it is shown that parametric disturbances of high frequency cannot create instability in an already asymptotically stable system. Also it is shown that slowly varying parametric disturbances will not cause instability if the system matrix is a stability matrix for all values of time. The results are applied to the Mathieu equation to illustrate the character of the theorems. This example is chosen because of the availability of its exact stability boundaries.
Shock Waves in Mathematical Models of the Aorta
Authors: Rudinger George
Published: April 2010

If the nonlinear equations for nonsteady blood flow are solved by the method of characteristics, shock discontinuities may develop as a result of omitting from the mathematical model some aspect of the system that becomes significant at rapid flow changes. As an illustration, the flow from the heart into the aorta at the beginning of systole is analyzed. An equation is derived which yields shock formation distances between a few centimeters and several meters depending on the elastic properties of the aorta. Since knowledge of the actual wave form would be useful for computer programming, a few exploratory experiments were performed with an unrestrained latex tube. They indicated wave transitions extending over several tube diameters, but maximum steepening of the wave has not yet been achieved.
A Stability Theorem for Mechanical Systems With Constraint Damping
Authors: Mingori D. L.
Published: April 2010

The effect of energy dissipation on the stability of motion of a mechanical system is a topic that has received considerable attention over the past 100 years. Since the advent of artificial Earth satellites, investigations concerned with spacecraft stability have led to renewed interest in this subject. Whereas previous work has dealt almost exclusively with damping forces that may be classified as generalized velocity damping forces; i.e., damping forces that satisfy the inequality ∑i=1nQiq˙i≦0 where the Qi’s are nonconservative generalized forces and the q˙i’s are generalized velocities, it has been found recently that a more general description of damping is sometimes desirable. Damping forces not satisfying the previously mentioned inequality have been called “constraint damping forces.” In the present paper, a theorem useful in the study of systems with constraint damping is stated and proved. This theorem represents a generalization of the Kelvin-Tait-Chetaev theorem for systems with generalized velocity damping only.
Lower Bounds to the Eigenvalues in One-Dimensional Problems by a Shift in the Weight Function
Authors: Pnueli D.
Published: April 2010

A method is presented to obtain both upper and lower bound to eigenvalues when a variational formulation of the problem exists. The method consists of a systematic shift in the weight function. A detailed procedure is offered for one-dimensional problems, which makes improvement of the bounds possible, and which involves the same order of detailed computation as the Rayleigh-Ritz method. The main contribution of this method is that it yields the “other bound;” i.e., the one which cannot be obtained by the Rayleigh-Ritz method.
Derivation of First-Order Difference Equations for Dynamical Systems by Direct Application of Hamilton’s Principle
Authors: Vance J. M. , Sitchin A.
Published: April 2010

In dynamics problems where the equations of motion are eventually reduced to finite-difference equations for numerical integration on a digital computer, an auxiliary condition exists that permits the application of the Lagrangian multiplier method to Hamilton’s principle in order to obtain directly a set of first-order difference equations. These equations are equivalent to Hamilton’s canonical equations and are derived without the necessity to obtain the Hamiltonian or take time derivatives.
Separation at the Interface of a Circular Inclusion and the Surrounding Medium Under an Incident Compressive Wave
Authors: Achenbach J. D. , Hemann J. H. , Ziegler F.
Published: April 2010

Separation at the interface of a circular inclusion embedded in a matrix of lower characteristic impedance and subjected to incident compressive waves is investigated, both experimentally and analytically. In the experiment, the compressive waves were generated by small explosive charges. For small charges, separation was not observed. As the explosive charge was increased, separation was observed at the “shadow side” of the inclusion. For still higher charges, separation was observed at the front face as well as at the shadow side of the inclusion. The qualitative analytical treatment is based on the methods of propagating stress discontinuities. It is shown that a compressive stress wave is converted into a tensile wave after a refraction and a reflection inside the inclusion. The reflected discontinuity of the tensile stress at the wave front is magnified upon passage through a focal point before reaching the shadow side of the inclusion. A divergence factor in conjunction with the closer proximity of the caustic to the back face reduces the level of tensile stresses reaching the front face. Separation is thus less likely to occur at the front face, which was verified experimentally. The results of this paper apply to the behavior of fiber-reinforced composites under dynamic loading conditions.
Concentrated Forces on Shallow Cylindrical Shells
Authors: Sanders J. Lyell , Simmonds J. G.
Published: April 2010

Solutions for the normal displacement w and tangential displacements ux and uy for a shallow cylindrical shell subjected to concentrated forces are obtained in this paper. The normal force and the two tangential force cases are treated. The results for the displacements in all cases are expressible in terms of elementary functions, modified Bessel functions, and one new function of two variables. A reasonably complete investigation of this function is included.
Buckling of Vessels Composed of Combinations of Cylindrical and Spherical Shells
Authors: Harari A. , Baron M. L.
Published: April 2010

This paper considers the buckling of vessels which are composed of a cylindrical shell closed by hemispherical shell end caps. Such structures have been considered for deep submergence research vehicles. Numerical results for the buckling loads are obtained and compared with experimental results from the Naval Ship Research and Development Center. It is seen that the comparison of theory and experiment is quite good.
Derivation of Torsion Formulas for Multiply Connected Thick-Walled Rectangular Sections
Authors: Marshall J.
Published: April 2010

The paper presents an approximate theory leading to expressions relating torque, shear stress, and angle of twist for the torsion of multiply connected thick-walled rectangular hollow sections. Simple formulas are derived for singly connected sections which are shown to be reasonably accurate for design purposes. In the Appendix, a numerical example illustrates the application of the theory to a multiply connected section.
Deformation Bounds for Bodies Which Creep in the Plastic Range
Authors: Leckie F. A. , Ponter A. R. S.
Published: April 2010

Previous results on bounding the energy dissipation of bodies which creep have been extended to include plastic deformations. The theorems, which are derived, show that previous results can be used, provided the stress fields which are selected nowhere exceed the value of the ratio n/n + 1 of the yield condition for stress.
A Numerical Computation of a Confined Rotating Flow
Authors: Pao Hsien-Ping
Published: April 2010

A numerical investigation of a viscous incompressible fluid confined in a closed circular cylindrical container is made. The top and side wall are in rotation with a constant angular velocity, and the bottom is held fixed. A numerical scheme using the full Navier-Stokes equations is developed. For small or moderate Reynolds numbers (Re = ΩL2/ν), the convergence of iteration is quite rapid. When the Reynolds number increases, the flow in the bottom boundary layer and the viscous core is intensified. An initial value problem is also investigated for Re = 1000 and 5000. The flow development of the bottom boundary layer and the viscous core is clearly exhibited. Some experimental investigation is also made. The numerical solution agrees very well with the analytic solution for small Reynolds numbers and with the experimental observation for moderate and high Reynolds numbers.
Application of Point Matching Techniques to Two-Dimensional Solidification of Viscous Flow Over a Semi-Infinite Flat Plate
Authors: Miller M. L. , Jiji L. M.
Published: April 2010

An analytical method is presented for the solution of two-dimensional solidification of fluid in motion over a semi-infinite plate. The method is applicable to other two-dimensional free boundary problems involving convection of the liquid phase. The solution is based upon an instantaneous source method which transforms the moving free boundary problem to a stationary domain. The transformed problem is solved by a Laplace transformation which results in a two-dimensional elliptic problem in an irregularly shaped region. An approximate point matching method is employed to solve the elliptic problem. Interface motion is obtained from the solution of a nonlinear integrodifferential equation of the Volterra type. Numerical solutions are presented to verify the validity of the model used in the analytical method and to examine the accuracy of the analytical solution.
On the Almost Sure Stability of Linear Stochastic Systems
Authors: Man F. T.
Published: April 2010

A new sufficient condition for the almost surely asymptotic stability of ergodic coefficient linear stochastic systems is presented and is compared with previously published results. Two examples are given to illustrate the sufficient condition thus derived and to demonstrate the considerable extension, using this method, of the region of stability over the existing results.
Mobility and remote scattering in buried InGaAs quantum well channels with high-k gate oxide
Authors: Nagaiah P. , Tokranov V. , Yakimov M. , Koveshnikov S. , Oktyabrsky S. , Veksler D. , Tsai W. , Bersuker G.
Published: April 2010

The authors present results on the Hall electron mobility in buried In0.77Ga0.23As quantum well channels influenced by remote scattering due to In0.53Ga0.47As/HfO2 interface. When the top In0.53Ga0.47As/InAlAs barrier thickness was reduced from 50 to 0 nm, the mobility degraded from 12 000 to 1200 cm2/V s while the slope of its temperature dependency in the 77–300 K range changed from the conventional negative (∼T−1.2-phonon-driven mechanism) to positive (∼T). The mobility degradation is attributed primarily to remote Coulomb scattering due to the fixed charges at the semiconductor/oxide interface, as followed from the simulation results. The mobility reaches maximum at a sheet carrier density value of 2×1012 cm−2. The data indicate that passivation of InGaAs/HfO2 interface with in situ grown amorphous SiOx strongly improves mobility.
Comparative study between erbium and erbium oxide-doped diamondlike carbon films deposited by pulsed laser deposition technique
Authors: Foong Y. M. , Hsieh J. , Li X. , Chua Daniel H. C.
Published: April 2010

Diamondlike carbon (DLC) films doped with the same fraction of erbium and erbium oxide were prepared by using 248 nm KrF pulsed laser deposition system. The effects of erbium and erbium oxide on the surface morphology, microstructures, and mechanical property of DLC were investigated. Transmission electron microscopy showed that both erbium and erbium oxide retained their initial oxidation states while embedded as metal or metal-oxide nanoclusters in an amorphous matrix. Atomic force microscopy showed that erbium-doped and erbium oxide-doped DLC films were smooth with rms of less than 0.2 nm and closely resembled pure DLC film. The Raman analysis showed broad peaks centering around 1550 cm−1 on both samples. The deconvoluted Raman spectra showed that the ID/IG value of DLC film increased from 0.38 to ∼0.55 in the presence of erbium and erbium oxide, and the estimated sp3 content for the DLC nanocomposite films was ∼56%–57%. X-ray photoelectron spectroscopy (XPS) confirmed that the C 1s peaks for DLC nanocomposite were slightly shifted from 285.2 eV (diamond) to 284.5 eV (graphite). The deconvolution of XPS spectra further confirmed the amount of sp3 content and revealed the presence of a higher fraction of SiC bonding in erbium oxide-doped DLC film. Microscratch tester results showed that the presence of erbium oxide improved the adhesion strength of DLC film from ∼1.72 to ∼2.19 N, which was more effective than erbium at the same concentration (∼1.89 N). The coefficients of friction of the erbium-doped DLC and erbium oxide-doped DLC films were similar to that of pure DLC. Erbium and erbium oxide showed similar influence on the surface roughness, coefficient of friction, and sp3 content on DLC films, but improved adhesion strength, which was correlated with the SiC bonding states, was observed on erbium oxide-doped DLC.
SU‐DD‐A1‐05: Study of VMAT Plan QA Using Film, Diode Based, and Ion Chamber Based QA Systems
Authors: Cao D , Chen F , Rao M , Afghan M , Ye J , Shepard D
Published: April 2010

Purpose: With the commercial introduction of delivery control systems for Volumetric Modulated Arc Therapy (VMAT), the need has arisen for reliable and efficient techniques for performing patient specific VMAT quality assurance (QA). In this work, we have studied three patient specific QA techniques for VMAT: ion chamber with film, 2D diode array, and a 2D ion chamber array. Materials and Methods: The three QA techniques we have utilized are: (1) a stack of solid water slabs with an inserted ion chamber and film sandwiched between two slabs; (2) a 2D diode array (MapCHECK™ device inserted into a MapPHAN™ phantom); and (3) a 2D ion chamber array (MatriXX™ inserted into a MULTICube™ Phantom). Ten VMAT plans were delivered to all three QA systems on an Elekta Synergy linac. Results: With the highest spatial resolution among all three systems, film measurements can provide very good QA results when analyzed in relative mode. Absolute dose comparisons were performed for both the MapCHECK™ and MatriXX™ systems. The average passing rate in gamma analysis were 95.0% and 98.5% using 3%/3mm criteria for the above two systems, respectively. The slightly lower passing rate for MapCHECK™ QA may be attributed to the angular and dose rate dependence of the diode response. It is also observed that the MapCHECK™ QA is more sensitive to the tongue‐&‐groove effect when diodes fall between two leaves. The MatriXX™ system provides slightly higher QA passing rates. However it may be less sensitive to large dose variation within small regions due to its 7.62mm detector grid size. Conclusions: All three systems can be used for VMAT plan QA provided users are attentive about the strengths and limitations of the QA device.

Research sponsored by Elekta Corporation.
SU‐DD‐A2‐04: Use of the Adjoint Analysis Based Greedy Heuristic Algorithms in Treatment Planning for LDR Brachytherapy of the Prostate and HDR Brachytherapy Using Multicatheter Breast Implant Technique
Authors: Chaswal V , Thomadsen B , Henderson D
Published: April 2010

Purpose: To demonstrate use of the adjoint analysis based Greedy Heuristic (GH) algorithms in treatment planning for LDR brachytherapy of the prostate using directional sources and multicatheter‐HDR breast implant. Method and Materials: Two adjoint analysis based GH treatment planning tools are developed; The first, for a directional LDR brachytherapy application and the second, for a HDR‐multicatheter brachytherapy application. Both the problems have an extra degree of freedom compared with conventional, binary LDR treatment planning — the seed rotational orientation in directional LDR brachytherapy and the variable dwell‐time in HDR brachytherapy. The greedy heuristic treatment planning algorithm uses adjoint‐based ROI‐sensitivity‐fields to search for the best available source type and orientation, or dwell time increment at a source‐location in steps to build either a seed‐needle‐source‐orientation distribution or dwell‐location‐dwell‐time distribution solution non‐iteratively. The GH treatment planning for LDR technique is based on dose‐distribution optimization and that for HDR technique is based on dose‐homogeneity optimization. Results: The treatment plans generated by the greedy heuristic algorithm using the directional sources resulted in target coverage with V100 >98% and remarkably better OAR‐sparing owing to the directional dose properties of the sources, as seen from the DVH analysis and evaluation parameters comparison on 6 prostate cases when compared with conventional LDR‐brachytherapy. The multicatheter‐HDR brachytherapy dwell‐time optimization generated treatment plan with a target coverage V100 >96%, skin‐sparing (D85=4.5%), few hot‐spots and a dose homogeneity index of 0.82. Conclusion: Greedy Heuristic algorithms coupled with greedy criterions based on ROI‐sensitivity fields of dose response and dose‐homogeneity response are utilized as efficient tools for fast and reproducible treatment planning solutions in LDR and HDR brachytherapy.
SU‐DD‐A2‐05: A Conversion Method of Low Dose Rate to Pulsed Dose Rate Intracavitary Brachytherapy Prescription for the Treatment of Cervical Carcinoma
Authors: Mourtada F , Pung N , Gifford K , Lawyer A , Wendt R , White A , Eifel P
Published: April 2010

Purpose: To report on a retrospective clinical dosimetry analysis of the conversion of the low‐dose rate (LDR) to pulsed dose rate (PDR) intracavitary brachytherapy (ICBT). Methods and Materials: A tool was developed that converts an LDR prescription to PDR. This method incorporates the differences between LDR and PDR radial dose functions and includes perturbation factors of the different ICBT applicators as derived from MCNP Monte Carlo simulations. Absolute dwell time per PDR source position is calculated and entered into the Nucletron Plato TPS. A cohort of 67 LDR patients was randomly selected from our clinical GYN database. Plans were generated with Varian BrachyVision v6.5 for Selectron LDR sources, and with Nucletron Plato v14.1 for the PDR source. Doses were compared at the ICRU 38 patient points: Bladder, Rectum, A right and left, B right and left, 3 o'clock and 9 o'clock. A 5% difference between LDR and PDR doses at these points was considered significant. Results: In every case, the difference in dose between the LDR plan and the PDR plan was less than 5%. In addition, the differences in dose appeared to be randomly distributed about zero, implying that there was no systematic difference in the LDR and PDR dose points. Conclusions: A transfer method of our traditional LDR clinical program to PDR was validated. This insures our history with ICBT LDR experience is consistent for future ICBT patients undergoing PDR treatments.
SU‐DD‐A3‐02: Quantification of Heterogeneous Tumor Blood Volume as Early Predictors for Treatment Outcome in Advanced Head‐And‐Neck Cancer
Authors: Wang P , Popovtzer A , Eisbruch A , Cao Y
Published: April 2010

Purpose: To evaluate the predicting values of metrics that quantify poorly perfused tumor volumes in patients with advanced head‐and‐neck cancer (HNC) treated with chemo‐radiation therapy (chemo‐RT) for outcomes. Materials and Method: Dynamic contrast‐enhanced (DCE) MRI scans were acquired for thirteen patients treated with concomitant chemo‐RT for advanced HNC, before therapy and 2 weeks after start of therapy. Blood volume (BV) maps were computed from the DCE MRI. Fuzzy C‐means clustering analysis (FCM), a segmentation method for partitioning a dataset into multiple clusters by minimizing the intracluster distance among members, was utilized to analyze heterogeneous BV in primary tumor volumes. The pre‐treatment tumor BV (TBV) values from all patients were used as training data and partitioned into 2, 3, or 4 clusters using FCM; and the resulting prototype vectors were adopted to partition each individual TBV before and during therapy. The volumes of the clusters with the lowest BV values were tested for their associations with treatment outcome. In addition, the cut‐off BV values for the lowest 1 cc, 2 cc, or 5 cc primary tumor sub‐volumes were calculated at both time points; and their predicting values for treatment outcome were evaluated. Results: Four of the 13 patients had local failure. Eight metrics differentiate local failure vs. local control significantly: pre‐treatment cut‐off TBV for the lowest 5 cc (p=0.03); average cut‐off TBVs of the lowest 2 cc (p=0.01) or 5 cc (p=0.04) over pre‐ and during‐ treatment; the volumes of the lowest TBV cluster at pre‐treatment (p=0.02), during‐treatment (p⩽0.03), as well as the average value over pre‐ and during‐ treatment (p⩽0.03). Conclusion: Our results suggest that poorly perfused sub‐volumes of the tumor before and/or early after start of treatment differentiate local failure vs. local control. The metrics discovered here will be candidates for future larger studies.

Supported by NIHP01CA59827.
SU‐DD‐A3‐03: Can Prompt Gamma Emission During Proton Therapy Provide in Situ Range Verification?
Authors: Styczynski J , Riley K , Binns P , Bortfeld T , Paganetti H
Published: April 2010

Purpose: Prompt gamma rays emitted from proton‐nucleus interactions in tissue present a promising non‐invasive, in situ means of monitoring proton beam based radiotherapy. This study investigates the fluence and energy distribution of prompt gamma rays emitted during proton irradiation of phantoms. This information was used to develop a correlation between the measured and calculated gamma emission and the proton beam range, which would allow treatments to more effectively exploit the sharp distal falloff in the dose distributions of protons. Method & Materials: Measurements were performed at the Francis H. Burr Proton Therapy Center using a 5nA pencil proton beam, a homogeneous cylindrical Lucite phantom, and a lead collimated sodium iodide (NaI) detector arranged orthogonal to the beam. Emulating this experiment, a model of the phantom with a monoenergetic proton beam and an annular array of ideal photon tallies arranged orthogonal to the beam was developed using the Monte Carlo code MCNPX 2.6.0. Results: Experimental and computational results indicated a correlation between gamma emission and the proton depth‐dose profile. Several peaks were evident in the calculated energy spectrum and the 4.44MeV emission from was the most intense line having any apparent correlation with the depth dose profile. Arbitrary energy binning of 4–5MeV and 4–8MeV was performed on the Monte Carlo data; this binned data yielded a distinct emission peak 1cm proximal to the Bragg peak. In all cases in the Lucite phantom the position of the Bragg peak's 80% distal falloff corresponded with the position of the 4–8MeV binned 50% distal falloff. Conclusions: The results are promising and indicate the feasibility of prompt gamma emission detection as a means of characterizing the proton beam range in situ. This study has established the measurement and computational tools necessary to pursue the development of this technique.
SU‐DD‐A3‐04: Monte Carlo Simulation of a MicroCT‐Based Small Animal Radiotherapy System
Authors: Zhou H , Bazalova M , Rodriguez M , Keall P , Graves E
Published: April 2010

Purpose: A microCT‐based small‐animal‐radiotherapy system with a variable‐aperture collimator has been constructed, and a Monte Carlo model of this system has been developed. A series of Monte Carlo (MC) simulations were performed in order to calibrate the model against measured beam commissioning data. Method and Materials: The EGSnrc codes were used for MC simulation. The simulations included different source models, different apertures, and included or excluded the effect of the plastic cylindrical shell enclosing the CT bore. We considered sources including a circular x‐ray beam with spectra generated by Boone‐Fewell formula, and a simulated x‐ray tube with parameters fit to measured beam profile. The beam width was set to 2, 5, 10, and 20 mm. The depth dose in water and the beam profiles simulated with and without the CT bore were compared, and the calibration factor for the conversion from MC dose to the measured dose rate in water was computed. Results: The simulation showed that a model with 2.5 mm Al filtration matches the measured depth‐dose curves, with the mean error on all measurement points for 2.5 mm Al was 2.5%. The CT bore introduces a 6% attenuation but does not significantly affect the beam energy spectrum or depth‐dose characteristics. The low energy part of the spectrum from the x‐ray‐tube simulation varied substantially from that predicted by the Boone‐Fewell model. The conversion factor was found to be 7.7415×1018 particles/min. Conclusion: Models and parameters in the Monte Carlo planning system have been determined from the depth‐dose measurements and simulations. The observed effect of the CT bore suggested that the effect can be attributed to additional attenuation, which significantly simplifies the software complexity of the Monte Carlo planning system.
SU‐DD‐A4‐04: Predicting Tumor Local Control in Lung Cancer From Pre‐Treatment PET/CT Image Features
Authors: Vaidya M , Bradley J , Apte A , Yang D , El Naqa I
Published: April 2010

Purpose: The role of PET/CT imaging in radiotherapy treatment planning and monitoring has been increasing on a rapid pace. There is accumulating evidence that characteristics of pre‐treatment FDG‐PET could be utilized as prognostic factors to predict radiotherapy outcomes in different cancer sites. Direct standardized uptake value (SUV) measurements were traditionally used to assess risk. To improve our understanding of embedded information in PET/CT we are investigating an alternative image‐feature based approach for analyzing and predicting post‐radiotherapy local control in non‐small cell lung cancer (NSCLC) patients. Method and Materials: We analyzed pre‐treatment PET/CT scans of thirty‐one patients for the endpoint of local/loco‐regional failure. The Gross Tumor Volume (GTV) was considered as the region of interest (ROI). All patients underwent pre‐radiotherapy diagnostic PET/CT and the images were registered with their corresponding treatment planning CT. We studied the effect of motion artifacts using deblurring methods based on deconvolution with a 4D‐CT derived motion kernel. Features from the GTV region based on intensity‐volume histogram (IVH) metrics and texture characteristics were extracted from each CT image, PET image with and without motion correction. Results: About thirty candidate features were extracted for each case and were analyzed for assessment of patients' risk of failure. Our preliminary results indicate that IVH metrics and texture features could be potentially useful for failure prediction in NSCLC compared to volume and maxSUV. PET seemed to be more informative than CT in general. Motion correction affected the feature values and not the general trend in this data. Conclusion: We have explored new methods for analyzing failure risk in NSCLC from PET/CT data. Our results suggest a role for functional imaging based on image features in predicting risk of failure. However, further analysis of these variables and cross‐validation is still needed to determine which parameters are strong predictors of radiation treatment response.
SU‐EE‐A1‐05: Dosimetric Evalualtion of a Commercial Compensator for Spatially Fractionated Radiation Therapy
Authors: Stathakis S , Buckey C , Gutiérrez A , Mavroidis P , Esquivel C , Shi C , Mihailidis D , Papanikolaou N
Published: April 2010

Purpose: Spatially fractionated GRID therapy is utilized to treat large tumors by irradiating the volume through isolated small openings. The technique has shown high efficacy for bulky tumors, but it is used at relatively few facilities. In this study, we exploit the use of a prototype brass GRID, which could make GRID therapy more attractive to physicians and more widely available to patients. Method and Materials: A prototype GRID compensator was constructed by milling divergent holes of 1 cm diameter at the isocenter in a cube of brass. The GRID block is manufactured so that it can irradiate a maximum field size of 25×25cm2. Measurements for the characterization of the dosimetric properties of the GRID were performed using a Varian 23Ex linac, in a solid water phantom at 100cm SSD, for both 6MV and 18MV. Radiographic films were placed perpendicular to the beam axis to obtain lateral profiles, and parallel to the beam axis to find the percent depth doses (PDDs). A pinpoint ion chamber under the central hole was used to find the output factors. Results: The profiles have an obvious peak and valley pattern, with transmissions under the solid portion of the block of approximately 15% for 6MV and 30% for 18MV. The PDDs are less penetrating than their open‐field counterparts, for both 6MV and 18MV when compared against the 10×10cm2 open field. Conclusion: This prototype brass GRID compensator is a viable alternative to the cerrobend compensators or MLC‐based fields currently in use. Its ease of creation and use give it decided advantages. We believe this compensator can be put to clinical use, and will allow more centers to offer GRID therapy to their patients.

Research sponsored by .decimal corporation.
SU‐EE‐A3‐01: Comparison of Six Manual and Automatic 4D CT Registration Methods for Lung SBRT Image Guidance
Authors: Wang B , Assayah J , Hinkle J , Joshi S , Salter B
Published: April 2010

Purpose: 4D CT is now widely used in radiation therapy for generating accurate ITV's or for facilitation of gated treatment delivery. It is, as yet, relatively unexplored for use as a potential tool for image guidance of SBRT of lung. Use of 4D imaging for image guidance in SBRT requires that we determine an acceptable method for fusing 2 4D data sets. Method and Materials: We compare five different manual and/or automatic 4D registration methods and present the comparison results for phantom and patient data: Individual phase‐to‐phase registration; Average of phase to phase; MIP‐to‐MIP; Average Intensity Projection; Auto‐segmentation with centroid; Manual GE SimMD methods. Phantom studies were performed using the CIRS Dynamic Thorax phantom (CIRS, Norfolk, VA). A 2‐cm target was set into motion with a periodic sinusoidal 3D motion inside the anthropomorphic phantom. The baseline motion envelope of the target for simulation day movement was 4.2 mm L/R, 6.0 mm A/P, and 14.0 mm I/S. The target was then re‐programmed to move with the same motion envelope, but shifted away from the simulation motion envelope centroid, for three scenarios: a) Axial (L/R and A/P) only shift; b) Longitudinal only shift; and c) combination of axial (L/R & A/P) and longitudinal shift. Results: Individual phase‐to‐phase fusions were within 2.4 mm for all phases, with some phases performing better than others. The average and AIP methods were seen to perform very similarly, and this seems reasonable when we consider that both are, essentially, averaging methods. The MIP‐to‐MIP and Manual fusion methods were least accurate, but still likely to be considered clinically acceptable. Conclusion: Multiple methods have been explored for registration of 2 4D data sets. The averaging methods were seen to perform best, but all performed within what would reasonably be considered clinically acceptable limits. The centroid method performed particularly well.
SU‐EE‐A3‐02: Imaging Guided Frameless Stereotactic RadioSurgery Using CBCT 6D Image Registration and 6D Couch On Novalis Tx™ System
Authors: Chang Z , Wang Z , Wu Q , Kirkpatrick J , Yin F
Published: April 2010

Purpose: To investigate localization accuracy for image‐guided frameless stereotactic‐radiosurgery (IG‐SRS) using CBCT 6D image registration and 6D‐couch on Novalis Tx system. Method and Materials: Novalis Tx system is a powerful radiosurgery system featuring BrainLAB 6D‐couch and Varian CBCT. In this work, we performed phantom and patient studies to investigate IG‐SRS with CBCT 6D guidance. In phantom studies, a head phantom was positioned on couch, scanned with CBCT, and matched with planning CT using 6D image registration. Matching results were used to test accuracy of CBCT 6D/6D match for correcting translational and rotational setup errors. In patient studies, 10 intracranial SRS cases were randomly selected. Patients were initially positioned with BrainLAB mask system with target‐positioning‐overlays (TAPO). Patients were then scanned with CBCT, and positions were adjusted based on CBCT. Discrepancies between CBCT 3D/3D match and 6D/6D match were quantitatively analyzed. Results: Phantom experiments showed that translational discrepancies in root‐mean‐square (RMS) were 0.39, 0.23, and 0.36mm along lateral, longitudinal, and vertical directions. Rotational discrepancies in RMS were 0.38°, 0.19°, and 0.22° in pitch, roll, yaw, respectively. In retrospective patient studies, setup displacements measured in RMS between BrainLAB TAPO and CBCT 6D/6D match were upto 2.5mm translationally and 1.0° rotationally. If positioning was corrected using CBCT 3D/3D match, translational discrepancies in RMS were <0.5mm except 0.71mm in vertical, and rotational displacements in RMS were 0.67°, 0.88° and 0.22° in pitch, roll, yaw, as compared with CBCT 6D/6D match. CBCT guided 6D correction was performed in two cases to achieve necessary positioning accuracy. After 6D adjustments, translational and rotational displacements of upto 4mm and 0.9° were measured in CBCT 6D/6D match were fully corrected using 6D‐couch. Conclusion: CBCT 6D/6D match offers unprecedented view to verify patient positioning in both translations and rotations. Combined with 6D‐couch, translational and rotational setup errors can be effectively minimized.
SU‐EE‐A3‐04: In Vivo Detection of the Anterior Rectal Wall Using a Scintillation Fluid‐Filled Rectal Balloon for Prostate Cancer Radiotherapy
Authors: Melancon A , Archambault L , Lee A , Kudchadker R , Zhang L , Beddar S , Titt U , Dong L
Published: April 2010

Purpose: The prostate and the anterior rectum interface is perhaps the most important landmark but the most difficult soft tissue region for localization in image‐guided procedures. The goal of this study is to utilize the detection of rectal dose as a surrogate for anterior rectal wall (ARW) localization for daily prostate patient set‐up without using an imaging method. Methods: In this study, we designed a sweeping MLC beam to scan the anterior‐posterior (AP) prostate‐rectum interface from the lateral directions. The dose response from the inside of rectum will be measured using liquid scintillator and associated fiber optics. To validate our design, a 3mm wide lateral MLC segment was designed to move across the prostate‐rectum interface, and the mean rectal dose was calculated for each position in 8 prostate cancer patients with endorectal balloon immobilization and daily CT image sets. Then the dose‐position response curve was measured daily and fitted to the reference relationship to determine the shift which best reproduces the reference dose‐position relationship relative to the isocenter. To validate this method, the predicted alignments using the dose‐position relationship were compared with the manual AP alignment of the ARW using our in‐house CT registration software. Feasibility of the sliding segment technique was tested in an IMRT phantom fitted with a cylindrical liquid scintillator filled tube, optic fibers, and photodiode for current generation and detection. Results: The mean agreement of the dose‐calculated alignments and the manual image registration was 0.76 millimeters. The primary source of uncertainty was the variation in the insertion of the endorectal balloon. Measured signal increased monotonically with beam position within the rectum and rectal dose. Conclusion: In vivo detection of the ARW is feasible without an on‐board x‐ray imaging technique to achieve better alignment to anatomically important soft tissue structures.
SU‐EE‐A3‐05: Mutual Information for Beams‐Eye‐View Lung Tumor Tracking Without Radiopaque Markers
Authors: Rottmann J , Aristophanous M , Park S , Berbeco R
Published: April 2010

Purpose: To keep safety margins in lung stereotactic body radiation therapy (SBRT) small and provide retrospective calculation of the delivered dose, the tumor motion should be monitored. We propose a tumor tracking algorithm that can estimate the tumor location from portal images taken during the treatment without the help of fiducial markers. Method and Materials: An algorithm based on a normalized mutual information technique was developed for tumor tracking. First a tumor template and a search region are identified on a DRR set reconstructed from a 4DCT acquired prior to the treatment. The set consists of 10 images relating to 10 equally sized breathing phase bins. The template is then used to track the tumor over the sequence of portal images. To estimate the tracking precision a dynamic thorax phantom was employed. Results: The phantom study showed a sub millimeter tracking accuracy in the superior‐ inferior direction for anterior‐posterior and lateral fields. In a preliminary retrospective patient study the algorithm was able to track the tumor motion throughout the whole image sequence. Manual verification yielded a tracking magnitude error of xy = (3.4 ± 0.8) mm. Furthermore the algorithm's robustness was tested with portal image sequences from two other patients with different tumor motion amplitude and contrast. The accuaracy was estimated by comparison with manual tracking and yielded xy = (1.7 ± 1.9) mm and xy = (1.2 ± 0.8) mm, respectively. Conclusion: The algorithm has shown great potential for markerless lung tumor tracking. First test results showed that it can perform tumor tracking on portal images and DRRs even if the tracking template was defined in the other modality respectively.

Conflict of Interest: Varian Medical Systems, Inc.
SU‐EE‐A4‐02: An Iterative Method of Modeling Multidetector CT (MDCT) Source From Measured CTDI Values: A Feasibility Study
Authors: Gu J , Caracappa P , Xu X
Published: April 2010

Purpose: To propose a method of using the Monet Carlo (MC) technique to model MDCT scanners from CTDI values so the assessment of organ doses can be performed more accurately and easily. Method and Materials: The MC code, MCNPX, was used to perform all the simulations. Several parameters influencing CTDI values were analyzed and prioritized. The modeling method starts with employing the preliminary parameters necessary to perform the single axial scan to obtain the calculated CTDI values. Along with a priority list, each parameter was adjusted by comparing MC calculated CTDI values with measured CTDI values. The iterative process is completed when the parameters yield results that match the calculated and measured CTDI values. The validated CT model was then integrated with patient phantoms to calculate the organ doses for a specific CT procedure. Results: It was found that, in the modeling procedure, there are actually only two main parameters that exhibit the greatest influence on the finally calculated CTDI values: the thickness of the bowtie filter (BTF) and the length of BTF semimajor axis. These two parameters were thus given the highest priority. The modeling algorithm involves a total of six parameters including anode angle, thickness of flat filter, width of BTF, thickness of BTF, length of BTF semimajor axis, and source number. Based on this method a MDCT was modeled and the calculated CTDI values within around 5% of the measured CTDI values. Conclusion: Results demonstrated the feasibility of this iterative method based on analysis and priorities of various parameters. To our knowledge, this work is among the first attempts to develop the modeling method only using CTDI values. The CT scanners therefore can be modeled without the common problem of lacking information of parameters, thus facilitating accurate and easy MDCT dose assessment.
SU‐EE‐A4‐05: Radiation Dose Reduction in CT Guided Cryoablation Using HYPR‐LR
Authors: Leng S , Liu X , Yu L , Atwell T , McCollough C
Published: April 2010

Purpose: Patients under CT guided interventional procedures usually receive high radiation dose as multiple scans are performed. The purpose of this study is to investigate potential of dose reduction for CT‐guided renal tumor cryoablation using a newly developed image reconstruction technique: Local HYPR Reconstruction (HYPR‐LR). Method and Materials: Three patients, each with a renal tumor, underwent percutaneous cryoablation with CT monitoring. Original full dose projection data sets were saved and exported to a personal computer. Noise was inserted into the projection data to simulate low dose scans (50% of the original dose) using a novel noise insertion tool developed by our lab. Low dose images at different freezing time were then reconstructed from the simulated low dose projections using commercial reconstruction algorithm. HYPR‐LR was conducted using the average low dose images as a composite image. Image quality, focusing on target (ice ball) visibility and image noise, was compared among full dose images (FD), low dose images (LD) and low dose HYPR‐LR images. Results: Low dose images reconstructed with HYPR‐LR demonstrate similar image quality as the full dose scan images and superior to the low dose images reconstructed with commercial software. Image noise measured at three set of images were: 51.3 (LD), 38.3 (FD), and 31.8 HU (HYPR‐LR). The growing ice ball can be better visualized in the HYPR‐LR image series compared to the low dose images due to improved image quality. Conclusion: HYPR‐LR has been demonstrated to be useful for dose reduction in renal tumor cryoablation with CT monitoring. Our study shows that at least a factor of 2 dose reduction is achievable by reducing the tube mAs by 50%. Clinically, this translates into a factor of 2 reduction in radiation risk (deterministic or stochastic) for the increasing numbers of patients undergoing CT‐guided tumor cryoablation.