bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of Apparatus for Constant-Stress or Constant-Load Creep Tests
Authors: Garofalo F. , Richmond O. , Domis W. F.
Published: November 2011

Apparatus has been designed and built for conducting creep tests under constant-stress or constant-load conditions. An exact mathematical solution describing the shape of the cam lever for constant stress is given. This solution applies for the large strains usually found for ductile metals and alloys, as long as the strain is uniform. The initial specimen length employed in a constant-stress creep test ordinarily is fixed by the dimensions of the cam system used. It is shown by the present analysis that the initial specimen length may be changed if an approximate adjustment is made in the initial setting of a properly designed cam lever. The direction of the load axis remains fixed and therefore the apparatus has the advantage of a more complex level-beam machine. The results of a number of creep tests under constant-stress conditions are reported.
Experimental Investigation of Subsonic Turbulent Flow Over Single and Double Backward Facing Steps
Authors: Abbott D. E. , Kline S. J.
Published: November 2011

Results are presented for flow patterns over backward facing steps covering a wide range of geometric variables. Velocity profile measurements are given for both single and double steps. The stall region is shown to consist of a complex pattern involving three distinct regions. The double step contains an assymmetry for large expansions, but approaches the single-step configuration with symmetric stall regions for small values of area ratio. No effect on flow pattern or reattachment length is found for a wide range of Reynolds numbers and turbulence intensities, provided the flow is fully turbulent before the step.
Performance Characteristics of Turbine Flowmeters
Authors: Shafer Montgomery R.
Published: November 2011

The general performance of turbine-type or propeller flowmeters operating on liquid hydrocarbons in the range 0.5 to 250 gpm is described. Particular characteristics investigated include the effects of flow rate, viscosity, pressure level, entrance flow pattern, and orientation on the performance of these meters. It is shown that metering precision better than 0.2 per cent can be attained for selected ranges of flow rate and viscosity when entrance conditions and meter orientation are suitably controlled. Other factors briefly reviewed include dynamic response, totalization considerations, and the readout instrumentation.
A Contribution to Liapunov’s Second Method: Nonlinear Autonomous Systems
Authors: Szego¨ G. P.
Published: November 2011

The stability of nonlinear autonomous systems with nonlinearity representable in polynomial form is investigated. For the case of locally stable systems the following theorem is presented: A sufficient condition for local stability of the system x˙ = X(x) is the existence of a definite function v = φ(x) such that dv/dt = θ(x)g[ξ(x)], where θ(x) is a semidefinite function not identically equal to zero on a solution of x˙ = X(x), g(x) is such that g(0) = 0 and sign g(u) ≠ sign g(−u), and ξ(x) = 0 is a closed surface. A procedure for constructing Liapunov functions based upon the use of a generating v-function is developed. Such a generating v-function may have the form: v(x)=x′A(x)x where A(x) = {aij(xi, xj)}, and aij = aji. The coefficients aij (xi, xj) can be computed in order to obtain dv/dt of the wanted form. Particular emphasis is given to the case of systems with limit cycles and, as an example, the limit cycle of the van der Pol equation is identified with good approximation. It is also analytically proved that outside a closed algebraic curve, circumscribing the limit cycle, the system is asymptotically stable.
Approximate Method for Calculating the Time Response in Linear, Time-Varying, and Nonlinear Automatic Control Systems
Authors: Naumov B.
Published: November 2011

In past years many methods have been developed for calculating the time response in automatic control systems. In this paper an improved, approximate method for calculating the transient response in linear (Section 1), time-varying (Section 2), and nonlinear (Section 3) automatic control systems, is developed on the basis of previous works [1–5]. The basis of this method lies in an approximate solution of integral equations by means of special tables which are given in the Appendix. These tables enable the user to shorten the time for calculation. This method also can be useful for obtaining programs for digital computers. In each part of the paper, examples are given to illustrate the use of this method. These examples are identical to those of Boxer and Thaler [4] and facilitate a comparison of the solution method developed in the paper with their z-transform approach.
Energy Versus Stress Theories for Combined Stress—A Fatigue Experiment Using a Rotating Disk
Authors: Findley W. N. , Mathur P. N. , Szczepanski E. , Temel A. O.
Published: November 2011

An experiment is described in which the strain energy at the critical location for fatigue failure is maintained constant while the stresses on a given plane of the material at the same location are caused to fluctuate. Apparatus developed to produce this condition consisted of a circular disk with a wide flanged rim which was loaded along a diameter by means of pivot-pad bearings. The disk was then rotated under a constant load to produce the desired fluctuation in stresses at the center of the disk while maintaining a constant strain energy at the center. The fact that fatigue cracks were developed in the region of constant strain energy was considered to indicate that a concept of a fluctuating strain energy as a basic theory of failure by fatigue under combined stresses is not tenable.
Investigation of Periodic Modes of Sampled-Data Control Systems Containing a Saturating Element
Authors: Meserve W. E. , Torng H. C.
Published: November 2011

A discrete sequence approach is presented in this paper for investigating the possible modes of sampled-data control systems containing a saturating element. This method enables the investigator (a) to determine whether or not a control system has certain periodic modes, and (b) if it does, to identify them exactly. This approach is applicable to a sampled-data control system of any order. It is extended to the cases where the form of feedback is other than unity.
Performance of Elastic, Centrally Pivoted, Sector, Thrust-Bearing Pads—Part I
Authors: Sternlicht B. , Reid J. C. , Arwas E. B.
Published: November 2011

This is the first of three papers on the results of a recently completed study of the performance of tilting pad thrust bearings. It describes a method of analysis that was worked out for these bearings, which includes viscosity variations in the fluid film and an approximate calculation of the pad deflections caused by the hydrodynamic pressures. Equilibrium of moments is satisfied, laminar and adiabatic conditions are assumed, and the lubricant is incompressible. The two subsequent papers of this series will describe: (a) The results of an analysis which includes a more rigorous determination of pad deflections caused by hydrodynamic pressures and thermal gradients. (b) A comparison of analytical results with experimental data obtained in full-scale bearing tests.
A Theoretical Investigation of Pressure Depression in Externally Pressurized Gas-Lubricated Circular Thrust Bearings
Authors: Mori Haruo
Published: November 2011

A theoretical explanation of the experimentally observed depression of the pressure profile in externally pressurized gas-lubricated circular thrust bearings is presented, based on a concept new to gas lubrication, that of the generation of a shock wave in the bearing clearance space. On the basis of an approximate mathematical model, the bearing pressure distribution and load capacity are determined, and the effects of several bearing parameters are discussed. Good qualitative agreement is found between the analytical results and available experimental data.
Extension of the Conducting Sheet Analogy to Externally Pressurized Gas Bearings
Authors: Licht L.
Published: November 2011

Incompressible, viscous flow in narrow passages bounded by parallel surfaces yields the two-dimensional Laplace equation, ∇2P = 0. The pressure field, load capacity, and lubricant flow of hydrostatic oil bearings can be readily determined by means of the electric analogy of the conducting sheet. The equation ∂∂xP∂P∂x+∂∂yP∂P∂y=0 characterizes laminar, isothermal flow of gas lubricants in otherwise geometrically identical bearings. It is shown that by means of suitable change of the dependent variable this equation can be reduced to the Laplacian form. The ensuing advantage is the extension of the conducting sheet analogy to externally pressurized thrust and journal guide bearings when the lubricant is a gas.
Gas-Tracer Method of Steady and Pulsating-Flow Measurement
Authors: Kemp J. F.
Published: November 2011

A method is described of measuring the bulk mass-flow rate in steady and pulsating air streams with the aid of a suitable tracer gas such as carbon dioxide. The method briefly involves controlled injection of the tracer into the main flow, mixing of the two flow media, and analysis of the mixture to determine the concentration of the tracer. The main flow is derived from the injection flow rate and from the concentration of the tracer in the sample mixture. An inexpensive infrared analyzer was constructed for determining mass concentrations of carbon dioxide in air ranging from 1/2 to 3 per cent. Results obtained by the gas-tracer method in both steady and pulsating streams were compared with those obtained by other methods of mass-flow measurement. A few possible practical applications of the measuring technique are discussed.
Particle Trajectories in a Gas Centrifuge
Authors: Kriebel A. R.
Published: November 2011

The motion of spherical particles injected into a cylinder of gas which rotates as a solid body has been studied. The particle trajectory is expressed explicitly as a function of two dimensionless parameters; an injection-velocity parameter and an inertial parameter which is roughly the ratio of centrifugal force to drag force on the particle. The main results are the dependence on particle size of the time for particles to be centrifuged and of deposition angle. These results indicate performance limitations for an idealized cyclone separator and a centrifugal particle-size analyzer. Experimental data are presented for an air centrifuge which was designed to approximate the analytical flow model. Reasonably good agreement with theoretically predicted deposition angles was found for spherical glass beads and irregularly shaped chalk crystals, even to Reynolds numbers in excess of the Stokes flow regime for which the analysis applies. Particles as small as 2 microns may be classified with the present centrifuge configuration; however, by modification it might be used to classify particles in the submicron-size range.
Theory of Scale Effects on Cavitation Inception on Axially Symmetric Bodies
Authors: O¯shima R.
Published: November 2011

On the assumption that the motion of incipient cavitation bubbles on geometrically similar bodies is dynamically similar, the relation between incipient cavitation number kdi and Reynolds number Re has been obtained from the dynamical similarity law deduced from the equation of the motion of spherical bubbles. A comparison of calculated values based on this theory with experimental data obtained by R. W. Kermeen and others shows good agreement at values of Reynolds number greater than the critical Reynolds number. Also, by comparing this theory with the formula by R. T. Knapp, concerning scale effects on cavitation inception, it is shown that Knapp’s formula is a special case of the present theory.
Regulation of a Hydraulic Turbine Calculated by Step-By-Step Method
Authors: Swiecicki Ignacy
Published: November 2011

Equations are developed to calculate speed and pressure transients of a hydraulic turbine during a load change. Water hammer, governor time, dashpot time, temporary speed droop, and promptness of governor response are taken into account. An example illustrates the application of equations to a step-by-step calculation.
An Energy Criterion for Low-Cycle Fatigue
Authors: Martin D. E.
Published: November 2011

A criterion for low-cycle fatigue is developed which supposes that the segment of strain hysteresis associated with work-hardening is a measure of damage. On the basis of this “damage” work criterion and assuming a linear work-hardening law, the well-known plastic strain-cyclic life equation, N1/2Δεp = C is derived. The constant C in this equation is evaluated by setting the total damage energy absorbed in N cycles equal to the damage work of a static tensile test. This method of predicting the constant C is in much better agreement with room-temperature strain-cycling data than the previously suggested method of plotting the fracture ductility at 1/4 cycle.
An Experimental Study of Vortex Chamber Flow
Authors: Holman J. P. , Moore G. D.
Published: November 2011

It is shown that a relatively simple analysis predicts the functional variation of temperature and pressure in a vortex chamber with radius and inlet velocity. The predicted variation is in good agreement with experimental observations. By assuming that the flow at the outside of the chamber occupies some effective flow area, which is essentially independent of flow rate, the inlet velocity may be expressed in terms of the chamber dimensions and the fluid properties at entrance. The effective flow area assumption is verified experimentally for two chamber exit configurations using air.
Generalized Multistage Axial Compressor Characteristics
Authors: Mellor G. L. , Root T.
Published: November 2011

Presented below is a method of calculating the off-design performance of multistage axial compressor characteristics that differs in concept from previous methods. A set of resulting calculations has certain general properties; namely, that it is independent of absolute stage work and flow coefficient, number of stages, and annulus geometry. The set depends only on a stage characteristic “shape” which is normalized so that the work and pressure coefficient is unity when the flow coefficient is unity. One set of tabulated results can be applied to many different designs. Two comparisons with experiment are presented below and the agreement is fairly good. An added benefit derived from this kind of general approach is that one gains physical understanding of the various regions of compressor operation. In this regard the concepts of “axial equilibrium” and “match point” have been developed which in the present context are defined in a precise, quantitative manner.
Cavitation Effect on the Discharge Coefficient of the Sharp-Edged Orifice Plate
Authors: Numachi F. , Yamabe M. , O¯ba R.
Published: November 2011

The object of this paper is to investigate the effects of cavitation on the discharge coefficient of sharp-edged orifice plates with reference to various degrees of cavitation as defined by a cavitation number. The experimental data described in this paper substantiate the fact that cavitation can exist to a minimum cavitation number of 0.2 without introducing errors in the orifice discharge coefficient in excess of the normal expected accuracy. In addition to this, it was found that the use of air-inhalation to suppress the vibration and noise from the cavitation had no effect on the discharge coefficient.
A General Method for Correlating Labyrinth-Seal Leak-Rate Data
Authors: Heffner F. E.
Published: November 2011

The proper selection of an optimum labyrinth seal for a given application depends upon an accurate estimate of the seal leak rate. Suitable accuracy, particularly for straight labyrinth seals, can only be obtained from actual seal tests. Testing a complete series of seals is time-consuming and expensive. A method for correlating test data is presented which allows calculation of the leak rates for an entire family of labyrinth seals on the basis of tests of only two characteristic seals. Leak rates predicted by the method are within 3 per cent of the basic test data.
Friction Characteristics of Sliding Surfaces Undergoing Subsurface Plastic Flow
Authors: Shaw Milton C. , Ber Abraham , Mamin Pierre A.
Published: November 2011

It is well known that the load of an ordinary friction slider is supported by a large number of surface asperities having a collective area that is small compared with the apparent area of contact. The metal in bulk beneath such surface asperities is elastically loaded. In many metalworking operations, such as wire drawing, extruding, rolling, and metal cutting, the bulk metal undergoes plastic deformation as sliding occurs. The influence of this subsurface flow upon the coefficient of sliding friction is discussed. A simple test procedure for studying the friction characteristics of sliding metal surfaces, one of which is being subjected to plastic flow in bulk, is described, and representative data are presented for both dry and lubricated sliding.
Machining Characteristics of Leaded Steel
Authors: Bagley Fenton L. , Mennell Roy
Published: November 2011

The effects of lead addition in alloy steel upon the metal-cutting process were explored over a wide range of conditions. In particular, a range of cutting speeds (from 50 to 800 fpm) and workpiece hardness (from 230 to 450 Bhn) were investigated on one work-piece material (4340) using principally a carbide (C-6) cutting tool. Orthogonal (two-dimensional) data was taken to describe the metal-cutting process, and tool-life data were obtained by running a typical production tool to failure at the various cutting conditions. Several mechanisms to explain experimental results, including lead acting as a lubricant, are discussed.
The Adiabatic Bulk Modulus of Normal Paraffin Hydrocarbons From Hexane to Hexadecane
Authors: Rolling R. E. , Vogt C. J.
Published: November 2011

A method for determining the sonic velocity in a fluid as a function of pressure and temperature is described. The method used measures the time required for an expansion wave to travel a known distance through the test medium. The results of the sonic velocity measurements are presented for normal hydrocarbons from C6 to C16 for temperatures and pressures from 60 to 250 F and 0 to 5000 psig, respectively. The density of the hydrocarbons was also determined. The absolute viscosity of the test compounds was determined by use of a rolling-ball viscometer for pressures from 0 to 6000 psig in the temperature range given. Tabulated and graphical results are presented for adiabatic bulk modulus, density, and absolute and kinematic viscosity for the range of hydrocarbons tested.
Low-Cycle Fatigue of Two Nickel-Base Alloys by Thermal-Stress Cycling
Authors: Mehringer F. J. , Felgar R. P.
Published: November 2011

Cast DCM and cast Udimet 500, two nickel-base alloys, were tested in a thermal-stress-cycling device of the Coffin type. The strains induced by the thermal stresses were analyzed in several ways in an attempt to relate the plastic strains to cyclic life. The plastic strains were too small to permit calculating them with sufficient accuracy to correlate with cyclic life. It was found, however, that stress range did correlate reasonably well with the number of cycles to failure.
On Cathodic Protection in Cavitation Damage
Authors: Plesset M. S.
Published: November 2011

An experimental procedure has been developed which makes possible accurate and reproducible determinations of cavitation damage. This procedure has been applied to a study of the effect of cathodic currents on cavitation damage. A series of experiments, in which the test liquid was a solution of salt in water, showed a reduction in cavitation weight loss for all of the materials examined when the test specimen was made the cathode of an electrolytic cell and when the conditions were such that gas was evolved at the specimen surface. This protective effect against cavitation damage increased with increasing magnitude of the cathodic current. These observations support the view that the protective effect was due to the layer of hydrogen gas evolved on the surface of the specimen. A similar protective effect was observed when the specimen was made the anode in a test liquid which was buffered distilled water; in this situation the gas evolved at the specimen surface is oxygen. Additional evidence for this protective mechanism of a gas layer on the specimen surface was found in a series of experiments in which the voltage applied to the cell was reduced to a level at which no gas was evolved on the surface. There was then no protective effect with the specimen cathodic or anodic.
Compliance and Longitudinal Strain of Cardiovascular Stents: Influence of Cell Geometry
Authors: Tan Tho Wei , Douglas Graeham R. , Bond Timothy , Phani A. Srikantha
Published: November 2011

A systematic study on the influence of the cell geometry of a cardiovascular stent on its radial compliance and longitudinal strain is presented. Eight stent cell geometries—based on common lattice cells—are compared using finite element analysis. It is found that, for a given strut thickness, the radial compliance depends on the shape of the cell and is intimately connected with the longitudinal strain through effective Poisson’s ratio, which depends on the cell geometry. It is demonstrated experimentally that a hybrid stent containing both positive and negative Poisson’s ratio cell lattice geometries exhibited very low values of longitudinal strain. This study indicates that cell geometries may be tailored to minimize longitudinal stresses imposed by the stent onto the artery wall.
SU‐C‐224‐05: Application of a Plastic Scintillation Detector in Measuring Depth‐Dose Curves for Passive‐Scattering Proton Beams
Authors: Wang L , Perles L , Archambault L , Sahoo N , Beddar S , Mirkovic D
Published: November 2011

Purpose: The plastic scintillation detector (PSD) has many advantages over other detectors in small field dosimetry due to its high spatial resolution, excellent water equivalency and instantaneous readout. However, in proton beams, the PSDs will undergo a quenching effect which makes the signal level reduced significantly when the detector is close to Bragg peak where the linear energy transfer (LET) for protons is very high. This study investigates the feasibility of using PSDs in depth‐dose measurements for clinical passive‐scattering proton beams. Methods: A polystyrene based PSD (BCF‐12, 0.5mm diameter and 4mm length) was used to measure the depth‐dose curves in a water phantom for pristine proton beams of nominal energies 100, 180, and 250 MeV. A Markus plane‐parallel ion chamber was also used to get the dose distributions for the same proton beams. From these results, the quenching correction factor (QCF) as a function of depth was derived for these proton beams. Next, the LET depth distributions for these proton beams were calculated by using the MCNPX Monte Carlo code, based on the experimentally validated nozzle models for these passive‐scattering proton beams. Then the relationship between the QCF and the proton LET could be derived as an empirical formula. Finally, the obtained empirical formula was applied to the PSD measurements to get the corrected depth‐dose curves and they were compared to the ion chamber measurements. Results: A linear relationship between QCF and LET, i.e. Birkˈs formula, was obtained for the proton beams studied. The PSD measurements after the quenching corrections agree with ion chamber measurements within 5%. Conclusions: PSDs are good dosimeters for proton beam measurement if the quenching effect is corrected appropriately.
SU‐C‐224‐08: The Calibration Accuracy of an Electromagnetic Tracking System to Radiation Isocenter
Authors: Litzenberg D , Gallagher I , Prisciandaro J , Lee C , Ritter T , Lam K
Published: November 2011

Purpose: To quantify the calibration accuracy of the Calypso System to radiation isocenter on systems at multiple sites. This data is being gathered under clinical conditions and will be used to refine margins used for treatment planning.Method: The electromagnetic tracking system is calibrated to isocenter with the manufacturers recommended technique, using laser‐based alignment. A test patient is created with a transponder at isocenter whose position is measured electromagnetically. Four portal images of the transponder are taken with collimator rotations of 45°, 135°, 225°, and 315°, at each of four gantry angles (0°,90°,180°,270°) with a 3×6 cm̂2 radiation field. In each image, the center of the copper‐wrapped iron core of the transponder is identified. All measurements are made relative to this transponder position to remove gantry and imager sag effects. For each of the 16 images, the 50% collimation edges are identified and used to find a ray representing the rotational axis of each collimation edge. The 16 rays pass through and bound the radiation isocenter volume. The center of the bounded region, relative to the transponder, is calculated and then transformed to tracking system coordinates using the transponder position coordinates, allowing the tracking systems calibration offset from radiation isocenter to be found. All image analysis and calculations are automated with in‐house software for user‐independent accuracy. Three different Calypso Systems at two different sites are being used for this study. Results: Two sets of data have been collected and analyzed to date. The positions of RF isocenter were found to be (LR,AP,SI)=(0.51,0.22,1.02)mm and (0.97,0.12,–0.77)mm, relative to radiation isocenter. The distances between radiation and RF isocenter were 1.16 and 1.24 mm. Conclusions: This method allows the calibration accuracy of the Calypso System to radiation isocenter to be determined. Preliminary results indicate an accuracy of about 1.2 mm. Supported in part by NIH grant P01‐CA59827
SU‐C‐BRA‐04: Experimental Feasibility Study on the Use of Scattering Foil Free Beams for Modulated Electron Radiotherapy
Authors: Connell T , Alexander A , Seuntjens J
Published: November 2011

Purpose: This work aims to investigate the feasibility of scattering foil free beams for use in energy modulated electron therapy. The main significance of this investigation is the potential reduction in photon contamination within the Bremsstrahlung tail region and its corresponding reduction in dose to healthy tissue. Method and Materials: A Varian (Varian Medical, Inc., Palo Alto, CA) 21EX linear accelerator was used in conjunction with an existing, custom‐built electron collimator to produce 8×8 cm2 and 2×2 cm2 fields at isocenter. The scattering foil was removed from the beamline by removing the port plug from one of the extra ports and manually rotating the empty port into the beamline. PDDs and profiles were acquired with and without the scattering foil. Measurement data was used to commission a Monte Carlo model of the accelerator and the model was incorporated into an in‐house designed inverse treatment planning system. Plans for each beamline were generated on a solid water test phantom consisting of a target and two organs at risk. DVHˈs were then compared for each plan. Results: PDD curves showed a dose reduction factor between 7.4 and 12.2 within the Bremsstrahlung tail region with the scattering foil removed. For quasi‐identical target coverage, removal of the scattering foil was able to produce superior organ at risk sparing in the optimized plans in the test phantom.Conclusion: This work has shown that by removing the scattering foil from the beamline in energy modulated electron therapy the component of Bremsstrahlung photons produced in the accelerator head is significantly reduced allowing superior plans that spare healthy tissue. The practical aspects of the dosimetry of these beams using the internal transmission ion chamber in the accelerator is a topic of further study.
SU‐C‐BRB‐01: Spatially Fractionated Radiation Therapy (GRID) Using a TomoTherapy Unit
Authors: Yan Y , Penagaricano J , Corry P , Moros E , Gardner K , Han EY , Zhang X , Chao M , Griffin Robert J. , Ratanatharathorn V
Published: November 2011

Purpose: To present a new technique to plan and deliver spatially‐fractionated radiotherapy (GRID) utilizing helical TomoTherapy IGRT system. Methods: In a single large dose (20 Gy), GRID offers an effective radiation therapy for bulky malignant tumors. The conventional GRID irradiation is delivered through a dedicated grid block or field intensity modulation using a multileaf collimator (MLC). However, the dose to nearby organs‐at‐risk (OAR) becomes a concern when treating deep seated bulky lesions in GRID technique. So With its capability of delivering highly conformal and multifocal dose distributions, TomoTherapy emerges as a promising radiotherapy modality for GRID therapy that delivers high single dose to deep seated tumors with excellent normal tissue sparing. It is called TOMO GRID. Planning CT images and contours are exported from a Pinnacle3 planning workstation via DICOM connection to the in‐house developed software system, DICOMan, where Boolean operations are applied to GTV contours to create multiple parallel GRID targets. An avoidance (GTV ‐ GRID targets) structure is also created to help the inverse planning process to achieve the desired peak‐valley ratio. Those CT images and contours will be repackaged in DICOMan and sent to TomoTherapy planning workstation.Results: TOMO GRID delivers highly non‐uniform dose distributions that resemble more or less those of breachytherapy. The TOMO GRID targets (virtual implants) can be configured in various patterns (templates), sectional shapes and sizes. At each “insert” position, the implant can be in either “needle” or “seed‐spacer” train. Tested in both phantom and real patient datasets, our results show that it is feasible to deliver GRID therapy on TomoTherapy unit for deep seated lesions Conclusions: TomoTherapy has a great potential to deliver GRID therapy with a superior quality than conventional GRID therapy. More studies need to be conducted to justify the applicability of this technology in clinics.
SU‐C‐214‐04: Variations in Tumor Motion Trajectory Due to Breathing Irregularity in 4D Cone Beam CT Using Prior Image Constrained Compressed Sensing (PICCS‐4DCBCT)
Authors: Qi Z , Chen G
Published: November 2011

Purpose: As breathing motion varies from cycle to cycle, the extracted motion profile from 4D Cone Beam CT represents an averaged motion over a number of breathing cycles. It is important to evaluate how the motion profiles extracted from 4DCBCT change with breathing cycle irregularity. In this study, we aimed to evaluate the robustness of 4D Cone Beam CT using the Prior Image Constrained Compressed Sensing method (PICCS‐4DCBCT). Methods: Numerical simulation studies were performed using a hybrid phantom. The phantom consists of in vivo human subject data and simulated lung cancer tumors with motion. Different types of breathing irregularity were simulated in this study, including irregular amplitudes, irregular periods, baseline drifts and the combinations of the above. These simulated cases represent realistic scenarios commonly observed in clinical practice. Because of the random nature of breathing irregularity, 10 experiments were conducted for each irregular case to achieve statistically meaningful results. After image reconstruction, a free‐form deformable registration method was applied to extract the motion trajectory of the sphere. With the regular motion trajectory as reference, the normalized root mean square error (nRMSE) is used to characterize the variation in the extracted average motion trajectory. Results: As the irregularity in breathing amplitude increases and more types of breathing irregularity are included, the variation in the extracted average tumor motion trajectory becomes larger. However, the normalized root mean square error is below 11% for all studied irregular cases. Conclusions: The study demonstrates that tumor motion profiles are robust against breathing cycle irregularity when the PICCS‐4DCBCT method is used.
SU‐C‐214‐05: 2.5 MV Cone‐Beam Computed Tomography with Thick CsI EPID
Authors: Tang G , Moussot C , Morf D , Seppi E , Amols H
Published: November 2011

Purpose: To evaluate the feasibility of CsI detector for low dose 2.5 MV cone‐beam computed tomography (MVCB). Methods: The new Varian TrueBeamTM at our center is equipped with a prototype non‐clinical 2.5 MV imaging system with a 9 mm thick cesium iodide (CsI) scintillator EPID. Both static portal radiographs and MVCB images can be obtained. The minimum dose per beam pulse or frame is ∼0.0025 cGy. Approximately 450 projections were collected at up to 9 frames/second in a full 360 degrees rotation that may take 60–90 seconds. MVCB scans of a RANDO phantom were acquired using 2.5 MV and 6 MV x‐rays, the latter taken with conventional EPID (aS1000, Varian Medical Systems). KVCB scans were also taken for comparative purposes. An acrylic phantom containing high‐Z inserts was imaged with all beams to assess image artifacts. Results: The new 2.5X prototype system required only ∼2.4–3.4 cGy to achieve clinically acceptable image quality in the head, thorax, and pelvis, while standard 6X MVCB required ∼26 cGy. Image quality approaching kVCB can be obtained with 2.5X MVCB using doses of ∼ 9cGy, although images acquired using 2.4 cGy were sufficient for bony alignment purposes. As expected, MVCB images in the head and thorax are superior to pelvis. In addition, the 2.5 MV imaging beam greatly reduces high‐Z image artifacts that can significantly perturb kV image quality. Conclusions: 2.5X MVCB with high quantum efficiency CsI detector can replace kVCB in most clinical situations at greatly reduced cost and fewer high‐Z artifacts. Unlike kV, treatment planning systems can easily incorporate MV dose into plan optimization. Further, patients having metallic implants (e.g. dental fillings, hip prosthesis, etc.) can benefit from MVCB due to its insensitivity to high‐Z materials and its ability to yield true electron densities for treatment planning.

Research partially supported by Varian Medical Systems.
SU‐C‐110‐04: A Clinical Evaluation of a Novel Hybrid Amplitude‐Based 4DCT Sorting Algorithm: Impact on ITV Delineation
Authors: Bellon M , Glide‐Hurst C , Chetty I
Published: November 2011

Purpose: The choice of sorting method used to genereate 4DCT image sets can affect image quality and target volume delineation. This study evaluated, in phantom and patient, the impact of a novel hybrid amplitude‐based (hAB) 4DCT sorting algorithm on the delineation of internal target volume (ITV), and results were compared with conventional phase‐based (PB) sorting .Methods: Eight phantom experiments were performed using respiratory motion platform programmed with simple ((1‐cos2), 5 second cycle) and complex (from RPM patient data) breathing curves with S‐I lung‐tumor excursion. 4DCT images were acquired, and corresponding datasets were sorted (10 phases) using both phase and hAB sorting algorithms. A retrospective study of nine early‐stage lung cancer patients were also reconstructed using both sorting algorithms, and maximum intensity projections (MIPs) were generated from each 4DCT dataset. ITVs for both phantom and patient data were auto‐contoured on each MIP. ITV volumes and centroids were compared between sorting algorithms. Results: For all phantom and patient studies, hAB produced smaller or equivalent ITVs than the PB approach. Average percent difference in delineated ITV volume was 5.2% (range: 0.0 – 13.5%) and 3.0% (range: 0.2 – 7.9%) for patient and phantom studies, respectively. For the patient study, the largest percent differences occurred when lateral or anterior‐posterior tumor motion was present. Average variation in centroid coordinates was < 1mm for all phantom and patient cases studied. The largest variation in ITV extent was expressed in the sup‐inf direction in the phantom study. Noticeable sorting artifact was observed for two phantom cases for both the hAB and PB sorted data Conclusions: This study demonstrates clinical application of a novel hAB 4DCT sorting algorithm. We have quantified the variation in ITV delineation stratified by sorting technique, and revealed situations which may increase the potential for the underestimation of full tumor volume extent encompassing motion.

Conflict of Interest: Henry Ford Health Systems holds a research agreement with Philips Medical Systems
SU‐C‐110‐06: Lung Tumor Volume Change and Correlation to Initial Size and Motion
Authors: Ewell L , Hepler C , Nguyen N , Elguindi S
Published: November 2011

Purpose: To quantify the volume change of lung tumors during the course of therapeutic radiation as a function of initial volume and respiration induced motion. Methods: Nine lung cancer patients were scanned on a Philips Big Bore Brilliance© CT scanner. They were subsequently rescanned after 4,000cGy of therapeutic lung tumor irradiation. Time dependence of the CT scans was obtained via placement of a bellows around the abdomen. Lung tumor lesions were contoured on inspiration (0% breathing phase) and exhalation (50% breathing phase) by a board certified radiation oncologist. Lesion volume and centroids were determined automatically via treatment planning software (Pinnacle© 9.0, ADAC Philips). External markers (BBs) were placed laterally and anterior to the approximate lesion location and formed a reference position. Results: The reference position in general had less than one mm of motion. The average initial distance from lesion centroid to the diaphragm was 9.3 ± 5.3cm (SD, range 0.57–21.18cm). Upon rescan, the average distance was 9.1 ± 4.8cm. The average initial tumor centroid motion was 0.10 ± 0.08, 0.21 ± 0.17 and 0.70 ± 0.63cm forthe left‐right, anterior‐posterior and superior‐inferior directions respectively. Upon rescan, the same averages were 0.11 ± 0.08, 0.25 ±0.16 and 0.65 ± 0.57cm. The average initial tumor volume was 27.6 ± 37.7cc (range 3.3 – 122.8cc). Upon rescan the average volume was 21.3 ± 30.9cc (range 0.5 – 97.1cc). For tumors whose volume was reduced by 40% or more (4 of 9, 44%), the ratio of superior‐inferior motion after rescan to before showed less variation than for the lesions whose volume changed less: 1.07 ± 0.36 vs. 0.79 ± 0.76. Conclusions: A trend was observed that suggests after 4,000cGy of therapeutic radiation, tumors with less volume change have less predictable motion change, than for tumors that experience a larger volume change.
SU‐C‐220‐05: Investigation of Novel, Focused, Segmented Scintillator Geometries for High DQE Megavoltage Active Matrix Imagers
Authors: Antonuk L , Liu L , Zhao Q , El‐Mohri Y , Jiang H , Street R
Published: November 2011

Purpose: Megavoltage active matrix, flat‐panel imagers (AMFPIs) have become ubiquitous in modern radiotherapy environments. However, their imaging performance is severely constrained by very low DQE (∼1%). While significant performance improvements have been demonstrated through introduction of thick, precision‐machined matrices of optically‐ isolated crystalline detector elements, the benefits are constrained by geometric beam divergence. It is therefore of interest to examine the potential performance of focused, segmented scintillator geometries specifically designed to circumvent DQE losses caused by divergence. Methods: The potential detection efficiency and DQE performance of hypothetical detector geometries was examined by means of Monte Carlo simulation of radiation transport. The choice of geometries examined was governed by considerations including: maximization of DQE through geometrically focused elements; manufacturability of the focused matrix; and feasibility of the underlying active matrix of indirect detection imaging pixels. Calculations were performed for a variety of candidate scintillator materials up to 6 cm thick. Results: The most promising detector geometries identified in the study consisted of matrices of scintillator elements located along the surface of a plane, as well as along the surface of a spherical cap. For cap detectors, elements arranged in a warped‐rectangular matrix, concentric rings, and a geodesic are of interest — and geometries employing a single element shape are particularly favored, although at the cost of fill factor. While focused planar detectors would be compatible with conventional AMFPI arrays, cap detectors would involve active matrix arrays in the shape of an approximately spherically curved surface created through cut and bend techniques. Overall, depending upon detector geometry, scintillator material and scintillator thickness, calculations indicate that DQE improvements of up to a factor of ∼50 are conceivable. Conclusions: This initial theoretical study suggests that the promise of very high DQE performance from thick, segmented scintillators could be realized through novel, focused detector geometries. Work supported by NIH grant R01‐CA051397
SU‐D‐BRB‐03: All‐Inclusive DOSXYZnrc Source for Monte Carlo QA of External Beam Radiotherapy
Authors: Alexander A , Renaud M , Seuntjens J
Published: November 2011

Purpose: To extend the versatility and simplicity of external beam Monte Carlo (MC) methods within BEAMnrc/DOSXYZnrc with the introduction of a new universal DOSXYZnrc source for multi‐field simulations. Methods and Materials: A single DOSXYZnrc source, capable of simulating all types of external beam radiotherapy, was developed as an extension to the standard set of sources. The source incorporates dynamic movement of components such as MLC leaves, jaws, gantry, collimator and couch. This was achieved by coupling the field index between the BEAMnrc components with the field index of the DOSXYZnrc components through the LATCH variable, transferred from BEAMnrc to DOSXYZnrc via the phase space information. This allows the state of the accelerator (such as MLC leaves, jaw positions and angles of incidence) to be changed for each history, effectively simulating coupled time‐dependent geometries. The process for RapidArc is as follows. RapidArc fields are defined within the control points of the DICOM plan file. Each point defines a MLC pattern and gantry angle. Within the MC simulation, the MLC pattern was defined in BEAMnrc, while the gantry angles were defined in the new DOSXYZnrc source. Control points for Tomotherapy are defined with the XML and sinogram files. In addition, IMRT and conformal treatments such as SBRT, which are comprised of 1–7 beams, can be merged into a single simulation. For practical considerations, it is more efficient to run a single MC simulation than to manage the submission of multiple beams and recombining them afterwards. We tested the new source within the context of the MMCTP system.

Results and Conclusion: This source has enabled MC plan verification of RapidArc and Tomotherapy and simplified the MC calculation of IMRT and SBRT into a single simulation for efficient QA. The new source adds much needed functionality to the existing set of DOSXYZnrc sources.
SU‐D‐BRB‐04: A Monte Carlo Based Approach to Electron Beam Treatment Planning
Authors: Mitrou E , Alexander A , Deblois F , Thebaut J
Published: November 2011

Purpose: Electron radiotherapy (RT) offers a number of advantages over photons. The high surface dose, combined with a rapid dose fall‐off beyond the target volume presents a net increase in tumor control probability and decreases the normal tissue complication for superficial tumors. The current techniques involving electron RT are more seldom used than photon therapy due to the complexity of the electron transport involved and greater error in planning accuracy. Electron treatments are normally delivered clinically without previously calculated dose distributions. Our current research aims to use Monte Carlo (MC) methods to model clinical electron beams in order to accurately calculate electron beam dose distributions in patients. In addition to this, electron output factors can be quickly calculated, reducing the need for a clinical measurement. Methods: The present work is incorporated into a research MC calculation system: McGill Monte Carlo Treatment Planning (MMCTP) system. MMCTP streamlines the calculation of output factors for various electron beam energies and applicator sizes. Measurements of PDDs, profiles and output factors in addition to 2D EBT‐2 GAFCHROMIC measurements in heterogeneous phantoms were obtained to commission the electron beam model. Results: Forty‐nine output factors were measured and calculated. The mean percentage difference between measured and calculated was 1.35% with a maximum of 3.27%. The mean error and calculation time of the calculations were found to be 1.64% and 2 hours respectively. A dose difference of 3% and distance‐to‐agreement of 3 mm were used to compare two dimensional dose maps using the gamma method, yielding a good outcome. Conclusions: The use of MC for electron TP will provide more accurate treatments and yield greater knowledge of the electron dose distribution within the patient. The calculation of output factors could invoke a clinical time saving of up to 1 hour per patient.
SU‐D‐BRB‐06: G4DBR: A Fast Geant4‐Based Monte Carlo Dosimetry Platform for Brachytherapy
Authors: Afsharpour H , Carrier J , DˈAmours M , Enger S A. , Landry G , Poon E , Verhaegen F , Beaulieu L
Published: November 2011

Purpose: To present, G4DBR, a fast Geant4‐based Monte Carlo (MC) dosimetry platform for brachytherapy. The special case of low dose rate (LDR) brachytherapy is considered here. Methods: Geant4 9.3 has been used for designing a new MC platform for calculating the dose distribution in brachytherapy called G4DBR. This code is capable of dealing with the DICOM RT format to build a virtual representation of each patient with the full multi‐seed configuration. The dose is scored both to medium and to water using track‐length estimator. The dose distributions are extracted in 3ddose format for visualization or to calculate the DVHs. Results: One prostate permanent 125I seed (PPSI) and one breast permanent 103Pd seed implant (BSPI) patient have been selected for evaluating the performance of G4DBR on a 2.93 GHz Intel Xeon Nehalem single core. Post‐implant dosimetry of those cases are performed in a 2 mm3 mesh for comparison with BrachyDose and MCPI. 45 seconds were required for G4DBR to reach a statistical uncertainty of 2% on PTV dose in PPSI. Note that for a similar precision, BrachyDose requires 30 seconds on 3 GHz Woodcrest (Thomson et al. Med. Phys. 2010) while MCPI needs 59 seconds on a single 2.4 GHz Pentium 4 CPU (Chibani et al. Med. Phys. 2005). G4DBR takes 114 seconds to attain a statistical uncertainty of less than 2% in the BPSI case. Conclusions: G4DBR is accurate and fast enough for clinical purposes. G4DBR is able to achieve good calculation speeds comparable with BrachyDose and MCPI. Indeed, a statistical uncertainty of less than 2% is attained in 45 seconds in a prostate case while 118 seconds were needed in BPSI to achieve 0.5% of uncertainty. Further developments will include the incorporation of high dose rate (HDR) dosimetry and a user‐friendly GUI for G4DBR.