bluuebunny/crossref_metadata_2025 huggingface dataset:
THE VALUE ADDED BY BANK ACQUISITIONS: LESSONS FROM WELLS FARGO'S ACQUISITION OF FIRST INTERSTATE
Authors: Houston Joel F. , Ryngaert Michael D.
Published: April 2005

Wells Fargo's recent acquisition of First Interstate Bancorp represents one of the relatively uncommon cases in which the economic values of both the acquiring and acquired banks increased sharply upon announcement of the deal. The transaction is also one of the few cases where the bidder in a major bank acquisition chose purchase instead of pooling accounting–despite the fact that the deal was openly hostile and that Wells Fargo had to fight off a competing bid from First Bank Systems.

Based on the stock market's reaction to this merger battle, as well as the results of their study of 153 bank mergers over the period 1985–1991, the authors argue that the most promising mergers are those presenting large opportunities to reduce costs by eliminating redundant operations. The stock market is much less responsive to other merger rationales such as diversification or entry into new markets in pursuit of growth.

The Wells case also suggests that a preoccupation with the accounting treatment of a merger is a mistake if it becomes the primary reason for turning down a deal that creates economic value, or if it prevents the bidder from choosing the lowest‐cost method of financing the deal. Throughout the bidding contest for First Interstate, the stock market responded positively to the success of Wells Fargo's efforts, even though purchase accounting would have a large adverse impact on reported earnings.

But if the stock market does not appear to care about the accounting treatment of a merger, the method of financing does appear to matter to investors. In general, acquisitions financed with cash are viewed more favorably by the market than stockfunded transactions. The evidence also suggests, however, that acquiring firms can reduce the negative impact of stock deals by making conditional offers (those in which the number of shares depends on the stock price performance of the acquirer) and by combining such offers with stock repurchase programs.
EVA® FOR BANKS: VALUE CREATION, RISK MANAGEMENT, AND PROFITABILITY MEASUREMENT
Authors: Uyemura Dennis G. , Kantor Charles C. , Pettit Justin M.
Published: April 2005

This article presents a complete ranking of America's 100 largest bank holding companies according to their shareholder value added. This research, the first of its kind for the banking industry, defines an EVA measurement for banks and presents evidence of EVA's stronger correlation with bank market values than traditional accounting measures like ROA and ROE.

Besides developing EVA and MVA as analytical tools for viewing the economic performance of the organization from a shareholder perspective, the authors also present a framework for calculating EVA at all levels of the organization, including lines of business, functional departments, products, customer segments, and customer relationships. The implementation of an EVA profitability measurement system at the business unit (or lower) level requires methods for three critical tasks: (1) transfer pricing of funds; (2) allocation of indirect expenses; and (3) allocation of economic capital. Although solutions to the first two are fairly straightforward, the allocation of capital to business units is a major challenge for banks today. In contrast to the complex, “bottom‐up” approach used by a number of large banks in implementing their RAROC systems, the authors propose a greatly simplified, “top‐down” approach that requires calculation of only the volatility of a business's operating profit (or NOPAT). The advantage of using NOPAT volatility is that it allows EVA analysis at any level of the organization in a way that captures the volatility effects from all sources of risk (credit, interest rates, liquidity, or operations).

While such a top‐down approach is clearly not meant to take the place of a comprehensive, bottom‐up RAROC analysis, it is intended to provide a complement–a high‐level “check” on the detailed, bottom‐up risk management procedures and controls now in place at most banks. Moreover, for those banks that have developed extensive funds transfer pricing, cost allocation, and RAROCstyle capital allocation systems, the EVA financial management system can either be integrated with those systems or serve as an independent economic assessment of the bank's business risks and returns.
UNDERSTANDING THE DESIGN OF CONVERTIBLE DEBT
Authors: Lewis Craig M. , Rogalski Richard J. , Seward James K.
Published: April 2005

There are now two dominant theories of convertible debt held by academic economists. One theory which has been called the “risk‐shifting” hypothesis–effectively views convertibles as an alternative to straight debt. The second–known as the “sig‐nalling” (or “backdoor‐equity”) theory‐treats convertibles as an alternative to ordinary equity. This article attempts to unify (or at least to illustrate the relationship between) these two theories by focusing on the design of the securities.

In structuring a convertible, managers and their investment bankers must make a variety of decisions. Besides the coupon rate, face value, issue size, and maturity, managers must also decide the conversion ratio (the number of shares promised per bond) and the amount of call protection afforded investors. Several of these design features have the effect of making a convertible more like a straight debt or a straight equity issue. The hypothesis underlying the authors' recent research is that the issuers of debt‐like convertibles are attempting to address a somewhat different financing challenge than the issuers of convertibles that behave more like equity. Their findings suggest that the primary aim of “debt‐like” convertible issues is to address investors' uncertainty and concerns about risk, whereas the main goal of “equity‐like” convertibles is to minimize the “information costs” associated with raising new equity.
MEASURING CORPORATE TAX RATES AND TAX INCENTIVES: A NEW APPROACH
Authors: Graham John R. , Lemmon Michael L.
Published: April 2005

Taxes play an important but underemphasized role in the valuation of a company and its projects. For example, the authors estimate that the expected tax benefits from interest deductions by all publicly traded U.S. corporations were responsible for almost $1.4 trillion of their total market value of $12.7 trillion in 1991. In the case of RJR's 1989 leveraged buyout alone, the capitalized value of the interest tax shield amounted to several billion dollars (or about 25%) of the company's market value.

This article argues that, to maximize shareholder wealth, the corporate planning process should include a careful analysis of corporate tax incentives. Using several examples, the authors show how earnings variability and major provisions of the tax code interact to affect a company's expected marginal tax rate. After describing the complexities involved in properly calculating corporate tax rates, the article concludes by describing a simulation method the authors have developed to measure a company's effective marginal tax rate and, hence, its tax incentives to use more leverage (or some other means of reducing taxable income).

In furnishing a method for calculating marginal tax rates with greater accuracy, the authors also provide a clue to resolving the capital structure puzzle discussed in the roundtable at the head of this issue. In particular, their recent research corrects earlier studies in the finance literature by showing that when marginal tax rates are measured before financing (that is, based on income before interest expense is deducted), there is a positive relation between debt usage and tax rates.
THE IMPACT OF ASSET SECURITIZATION: A PERSPECTIVE FOR INVESTORS
Authors: Okabe Robert M.
Published: April 2005

A securitization transaction creates a new set of analytical challenges for both investors in the asset backed securities (ABS) and for holders of the debt and equity of the sponsor. This article argues that investors can gain insights into the risk and expected rewards of both ABS and the sponsoring corporation's securities by focusing on the excess cash flow (or “residual interest”) that is expected to be generated by the ABS trust. The value of this residual interest is recognized as a one‐time gain by the sponsoring lender in the period the ABS transaction is closed. Because the assumptions used to calculate this gain should represent management's best estimates as to the performance of the loan pool, comprehensive analysis of the gain‐on‐sale calculation can provide both corporate and ABS investors with significant insight into the level of risk in the securities they own. It also offers a tool for determining whether the expected returns justify the risks.
CFAR: A NEW TOOL FOR PREDICTING CREDIT QUALITY
Authors: Wolkenfeld Suzanne
Published: April 2005

Because of the limitations of traditional analytical ratios based on book leverage and coverage ratios, Fitch IBCA established a credit rating methodology that gives primacy to cash flow measurements. Its approach focuses on the “cash flow adequacy ratio,” or CFAR. CFAR is based on the premise that companies generating strong cash flow from operations relative to maturing debt have better credit profiles than those forced to rely on outside sources of capital. CFAR serves as proxy for company's financial flexibility; the higher the CFAR, the more financial stress the company can withstand.

To assess the effectiveness of CFAR as a credit tool, Fitch IBCA surveyed 47 U.S. industrial companies with a Bloomberg composite rating of ‘A' from 1990–1995. Based on its cash flow analysis, the rating agency ranked the companies and predicted that many were likely to be upgraded or downgraded. In a three‐year period, 30% of the ratings in the sample group changed. Of the 14 ratings changes, Fitch IBCA forecast 10 correctly, which translates into a predictive score of over 70%.
An Analysis of Mixed Lubrication in Chemical Mechanical Polishing
Authors: Ng Sum Huan , Higgs, C. Fred , Yoon Inho , Danyluk Steven
Published: April 2005

Pressure and shear flow factors (Patir and Cheng, 1978) were used to take into account the roughness of the pad surface in the modeling of the interfacial fluid pressure during chemical mechanical polishing. An attempt was made to explain the physical meaning of the flow factors in this particular application. Additionally, a parametric study was carried out to see the effect on the model after the incorporation of the flow factors. The pressure and shear flow factors were found to have a competing effect on the magnitude of the sub-ambient fluid pressure.
Thermomechanical Analysis of Semi-infinite Solid in Sliding Contact With a Fractal Surface
Authors: Gong Z.-Q. , Komvopoulos K.
Published: April 2005

A thermomechanical analysis is presented for a semi-infinite elastic solid sliding against a rigid, rough surface characterized by fractal geometry. A piecewise-linear distribution of the contact pressure was obtained by superposition of overlapping triangular pressure elements. The normal surface displacements due to the effects of contact pressure, shear traction, and thermoelastic distortion caused by frictional heating are incorporated in the influence coefficients of the matrix-inversion method. Results for a smooth, cylindrical surface sliding over a semi-infinite elastic solid demonstrate the accuracy of the analysis and provide reference for comparison with results obtained with the rough (fractal) surface. The effects of surface topography and interaction between neighboring asperity microcontacts on the surface and subsurface temperature rise and stress field of the elastic semi-infinite solid are discussed in the context of numerical results. The significance of frictional heating on the contact pressure, temperature rise, and stresses is interpreted in terms of the Peclet number and topography (fractal) parameters. The results provide insight into the likelihood for cracking and plastic flow at the surface due to the combined effects of mechanical and thermal surface tractions.
Impact of a Rigid Sphere on an Elastic Homogeneous Half-Space
Authors: Yang J. , Komvopoulos K.
Published: April 2005

The impact of a rigid sphere moving at constant velocity on elastic homogeneous half-space was analyzed by the finite element method. Frictionless dynamic contact was modeled with special contact elements at the half-space surface. A dimensionless parameter, β, was introduced to study the effect of wave propagation on the deformation behavior. For small surface interference (β⩽1), the front of the faster propagating dilatational waves extends up to the contact edge, the real contact area is equal to the truncated area, and the contact pressure distribution is uniform. However, for large surface interference (β>1), the dilatation wave front extends beyond the contact edge, the real contact area is less than the truncated area, and the contact pressure exhibits a Hertzian-like distribution. The mean contact pressure increases abruptly at the instant of initial contact, remains constant for β⩽1, and increases gradually for β>1. Based on finite element results for the subsurface stress, strain, and velocity fields, a simple theoretical model that yields approximate closed-form relationships for the mean contact pressure and kinetic and strain energies of the half-space was derived for small surface interference (β⩽1), and its validity was confirmed by favorable comparisons with finite element results.
Wear Mechanisms of Untreated and Gamma Irradiated Ultra-High Molecular Weight Polyethylene for Total Joint Replacements
Authors: Zhou J. , Komvopoulos K.
Published: April 2005

Modification of the surface microstructure of ultra-high molecular weight polyethylene (UHMWPE) is essential for improving the wear resistance of orthopedic implants. A common approach is to cross-link the polymer by gamma irradiation. The objective of this study was to examine the tribological behaviors of untreated and gamma irradiated UHMWPE under physiologically relevant contact conditions. Emphasis was placed on the identification of the dominant wear mechanisms in the early stage of polymer wear. The irradiation dose exhibited a strong effect on the tribological properties of UHMWPE sliding against Co–Cr alloy in a bath of bovine serum. Transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM) were used to examine the microstructure and morphology of the worn surfaces. Regularly spaced folds with average spacing depending on the irradiation dose (i.e., cross-link density) formed on the wear tracks. Surface folding was related to plastic flow and the degree of mobility of the crystalline lamellae. SEM and TEM results elucidated the roles of the cross-link density and crystalline lamellae in the wear process. Based on the experimental evidence, a deformation model was obtained that provides explanation for the dependence of surface folding on the cross-link density and lamellae reorientation during sliding.
A Design of Crowning to Reduce Ball Passage Vibrations of a Linear Guideway Type Recirculating Linear Ball Bearing
Authors: Ohta Hiroyuki , Kato Soichiro , Matsumoto Jun , Nakano Kenta
Published: April 2005

This paper deals with a design of crowning to reduce the ball passage vibrations of a linear guideway type recirculating linear ball bearing (linear bearing) with the crowning length LC(1.2s⩽LC⩽1.7s, where s is the distance between the adjacent balls in the load zone). First, a fundamental condition to reduce the ball passage vibrations is provided. Second, a design method of the crowning by applying an approximate curve (an assumed functional formula) to the control points (satisfying the fundamental condition or being the intersection of straight and crowning areas of a raceway) is presented. Third, the design procedure is explained by giving an example. In the design example the power function crowning fits the control point best. In addition, the calculated amplitude for the power function crowning is lower than those for the circular arc crowning and the crowning of the commercial linear bearing. Finally, the validity of the presented design method is confirmed experimentally.
Perturbation Solution of Non-Newtonian Lubrication With the Convected Maxwell Model
Authors: Zhang Rong , He Xueming , Yang Simon X. , Li Xinkai
Published: April 2005

There are many studies on variations of the Maxwell model. Tichy (1996) discussed an admissible formulation of the Maxwell viscoelastic fluid model using a convected derivative and applied it to two-dimensional lubrication flow. Tichy obtained a solution using a regular perturbation in the Deborah number with the conventional lubrication solution as the leading term. This paper extends Tichy’s model by using a double regular perturbation to the convected Maxwell model. A correspondence solution can also be obtained. Our sliding velocity solution is different from Tichy’s solution; and a modified Reynolds equation is also different from that by Tichy.
An EHD Model to Predict the Interdependent Behavior of Two Dynamically Loaded Hybrid Journal Bearings
Authors: Fatu Aurelian , Hajjam Mohamed , Bonneau Dominique
Published: April 2005

An elastohydrodynamic (EHD) analysis is performed for two misaligned hybrid journal bearings working on the same shaft. To predict the correct system behavior we are forced to consider the interdependence between the two bearings and the shaft. The presented algorithm is based on finite element discretization. It allows accurate analysis of film breakdown and reforming, during the functioning of actual devices. Active (full film) and inactive (cavitated) film zones are determined for nonstationary running conditions. Using a convenient iterative solution procedure, the converged solutions for lubricant flow and elastic deformation fields are obtained. The analysis of thickness, pressure, power loss, and elastic deformation of both bearings and shaft surface allows the optimization of any parameter for the two hybrid bearings.
A Finite Element Study of Elasto-Plastic Hemispherical Contact Against a Rigid Flat
Authors: Jackson Robert L. , Green Itzhak
Published: April 2005

This work presents a finite element study of elasto-plastic hemispherical contact. The results are normalized such that they are valid for macro contacts (e.g., rolling element bearings) and micro contacts (e.g., asperity contact), although micro-scale surface characteristics such as grain boundaries are not considered. The material is modeled as elastic-perfectly plastic. The numerical results are compared to other existing models of spherical contact, including the fully plastic truncation model (often attributed to Abbott and Firestone) and the perfectly elastic case (known as the Hertz contact). This work finds that the fully plastic average contact pressure, or hardness, commonly approximated to be a constant factor of about three times the yield strength, actually varies with the deformed contact geometry, which in turn is dependent upon the material properties (e.g., yield strength). The current work expands on previous works by including these effects and explaining them theoretically. Experimental and analytical results have also been shown to compare well with the current work. The results are fit by empirical formulations for a wide range of interferences (displacements which cause normal contact between the sphere and rigid flat) and materials for use in other applications.
Cardiac cone‐beam CT volume reconstruction using ART
Authors: Nielsen T. , Manzke R. , Proksa R. , Grass M.
Published: April 2005

Modern computed tomography systems allow volume imaging of the heart. Up to now, approximately two‐dimensional (2D) and 3D algorithms based on filtered backprojection are used for the reconstruction. These algorithms become more sensitive to artifacts when the cone angle of the x‐ray beam increases as it is the current trend of computed tomography (CT) technology. In this paper, we investigate the potential of iterative reconstruction based on the algebraic reconstruction technique (ART) for helical cardiac cone‐beam CT. Iterative reconstruction has the advantages that it takes the cone angle into account exactly and that it can be combined with retrospective cardiac gating fairly easily. We introduce a modified ART algorithm for cardiac CT reconstruction. We apply it to clinical cardiac data from a 16‐slice CT scanner and compare the images to those obtained with a current analytical reconstruction method. In a second part, we investigate the potential of iterative reconstruction for a large area detector with 256 slices. For the clinical cases, iterative reconstruction produces excellent images of diagnostic quality. For the large area detector, iterative reconstruction produces images superior to analytical reconstruction in terms of cone‐beam artifacts.
Comprehensive Monte Carlo calculation of the point spread function for a commercial ‐Si EPID
Authors: Kirkby C. , Sloboda R.
Published: April 2005

Images produced by commercial amorphous silicon electronic portal imaging devices (‐Si EPIDs) are subject to multiple blurring processes. Implementation of these devices for fluence measurement requires that the blur be removed from the images. A standard deconvolution operation can be performed to accomplish this assuming the blur kernel is spatially invariant and accurately known. This study determines a comprehensive blur kernel for the Varian aS500 EPID. Monte Carlo techniques are used to derive a dose kernel and an optical kernel, which are then combined to yield an overall blur kernel for both 6 and 15 MV photon beams. Experimental measurement of the line spread function (LSF) is used to verify kernel shape. Kernel performance is gauged by comparing EPID image profiles with in‐air dose profiles measured using a diamond detector (approximating fluence) both before and after the EPID images have been deconvolved. Quantitative comparisons are performed using the metric, an extension of the well‐known metric, using acceptance criteria of 0.0784 cm (1 pixel width) distance‐to‐agreement and 2% of the relative central axis fluence . Without incorporating any free parameters, acceptance was increased from 49.0% of pixels in a cross‐plane profile for a 6 MV open field to 92.0%. For a physically wedged field, acceptance increased from 40.3% to 73.9%. The effect of the optical kernel was found to be negligible for these acceptance parameters, however for , we observed an improvement from 66.1% (without) to 78.6% (with) of scores (from 20.6% before deconvolution). It is demonstrated that an empirical kernel having a triple exponential form or a semiempirical kernel based on a simplified model of the detector stack can match the performance of the comprehensive kernel.
Effects of x‐ray and CT image enhancements on the robustness and accuracy of a rigid 3D/2D image registration
Authors: Kim Jinkoo , Yin Fang‐Fang , Zhao Yang , Kim Jae Ho
Published: April 2005

A rigid body three‐dimensional/two‐dimensional (3D/2D) registration method has been implemented using mutual information, gradient ascent, and 3D texturemap‐based digitally reconstructed radiographs. Nine combinations of commonly used x‐ray and computed tomography (CT) image enhancement methods, including window leveling, histogram equalization, and adaptive histogram equalization, were examined to assess their effects on accuracy and robustness of the registration method. From a set of experiments using an anthropomorphic chest phantom, we were able to draw several conclusions. First, the CT and x‐ray preprocessing combination with the widest attraction range was the one that linearly stretched the histograms onto the entire display range on both CT and x‐ray images. The average attraction ranges of this combination wereandin the translation and rotation dimensions, respectively, and the average errors wereand. Second, the combination of the CT image with tissue and bone information and the x‐ray images with adaptive histogram equalization also showed subvoxel accuracy, especially the best in the translation dimensions. However, its attraction ranges were the smallest among the examined combinations (on averageand). Last the bone‐only information on the CT image did not show convergency property to the correct registration.
ROC study of the effect of stereoscopic imaging on assessment of breast lesions
Authors: Chan Heang‐Ping , Goodsitt Mitchell M. , Helvie Mark A. , Hadjiiski Lubomir M. , Lydick Justin T. , Roubidoux Marilyn A. , Bailey Janet E. , Nees Alexis , Blane Caroline E. , Sahiner Berkman
Published: April 2005

An observer performance study was conducted to evaluate the usefulness of assessing breast lesion characteristics with stereomammography. Stereoscopic image pairs of 158 breast biopsy tissue specimens were acquired with a GE Senographe 2000D full field digital mammography system using a magnification geometry. A phantom‐shift method equivalent to a stereo shift angle of relative to a central axis perpendicular to the detector was used. For each specimen, two pairs of stereo images were taken at approximately orthogonal orientations. The specimens contained either a mass, microcalcifications, both, or normal tissue. Based on pathological analysis, 39.9% of the specimens were found to contain malignancy. The digital specimen radiographs were displayed on a high resolution MegaScan CRT monitor driven by a DOME stereo display board using in‐house developed software. Five MQSA radiologists participated as observers. Each observer read the 316 specimen stereo image pairs in a randomized order. For each case, the observer first read the monoscopic image and entered his/her confidence ratings on the presence of microcalcifications and/or masses, margin status, BI‐RADS assessment, and the likelihood of malignancy. The corresponding stereoscopic images were then displayed on the same monitor and were viewed through stereoscopic LCD glasses. The observer was free to change the ratings in every category after stereoscopic reading. The ratings of the observers were analyzed by ROC methodology. For the 5 MQSA radiologists, the average value for estimation of the likelihood of malignancy of the lesions improved from 0.70 for monoscopic reading to 0.72 after stereoscopic reading, and the average value for the presence of microcalcifications improved from 0.95 to 0.96 . The value for the presence of masses improved from 0.80 to 0.82 after stereoscopic reading, but the difference fell short of statistical significance . The visual assessment of margin clearance was found to have very low correlation with microscopic analysis with or without stereoscopic reading. This study demonstrates the potential of using stereomammography to improve the detection and characterization of mammographic lesions.
Brachytherapy needle deflection evaluation and correction
Authors: Wan Gang , Wei Zhouping , Gardi Lori , Downey Donal B. , Fenster Aaron
Published: April 2005

In prostate brachytherapy, an needle is used to implant radioactive seeds. This thin needle can be deflected from the preplanned trajectory in the prostate, potentially resulting in a suboptimum dose pattern and at times requiring repeated needle insertion to achieve optimal dosimetry. In this paper, we report on the evaluation of brachytherapy needle deflection and bending in test phantoms and two approaches to overcome the problem. First we tested the relationship between needle deflection and insertion depth as well as whether needle bending occurred. Targeting accuracy was tested by inserting a brachytherapy needle to target 16 points in chicken tissue phantoms. By implanting dummy seeds into chicken tissue phantoms under 3D ultrasound guidance, the overall accuracy of seed implantation was determined. We evaluated methods to overcome brachytherapy needle deflection with three different insertion methods: constant orientation, constant rotation, and orientation reversal at half of the insertion depth. Our results showed that needle deflection is linear with needle insertion depth, and that no noticeable bending occurs with needle insertion into the tissue and agar phantoms. A 3D principal component analysis was performed to obtain the population distribution of needle tip and seed position relative to the target positions. Our results showed that with the constant orientation insertion method, the mean needle targeting error was and the mean seed implantation error was . Using the constant rotation and orientation reversal at half insertion depth methods, the deflection error was reduced. The mean needle targeting errors were 0.8 and for the constant rotation and orientation reversal methods, respectively, and the seed implantation errors were 0.9 and for constant rotation insertion and orientation reversal methods, respectively.
Physical characteristics of a low‐dose gas microstrip detector for orthopedic x‐ray imaging
Authors: Després Philippe , Beaudoin Gilles , Gravel Pierre , de Guise Jacques A.
Published: April 2005

A new scanning slit gas detector dedicated to orthopedic x‐ray imaging is presented and evaluated in terms of its fundamental imaging characteristics. The system is based on the micromesh gaseous structure detector and achieves primary signal amplification through electronic avalanche in the gas. This feature, together with high quantum detection efficiency and fan‐beam geometry, allows for imaging at low radiation levels. The system is composed of 1764 channels spanning a width of and is capable of imaging an entire patient at speeds of up to . The resolution was found to be anisotropic and significantly affected by the beam quality in the horizontal direction, but otherwise sufficient for orthopedic studies. As a consequence of line‐by‐line acquisition, the images contain some ripple components due to mechanical vibrations combined with variations in the x‐ray tube output power. The reported detective quantum efficiency (DQE) values are relatively low (0.14 to 0.20 at ) as a consequence of a suboptimal collimation geometry. The DQE values were found to be unaffected by the exposure down to , suggesting that the system is quantum limited even for low radiation levels. A system composed of two orthogonal detectors is already in use and can produce dual‐view full body scans at low doses. This device could contribute to reduce the risk of radiation induced cancer in sensitive clientele undergoing intensive x‐ray procedures, like young scoliotic women.
Four‐dimensional radiotherapy planning for DMLC‐based respiratory motion tracking
Authors: Keall Paul J. , Joshi Sarang , Vedam S. Sastry , Siebers Jeffrey V. , Kini Vijaykumar R. , Mohan Radhe
Published: April 2005

Four‐dimensional (4D) radiotherapy is the explicit inclusion of the temporal changes in anatomy during the imaging, planning, and delivery of radiotherapy. Temporal anatomic changes can occur for many reasons, though the focus of the current investigation is respiration motion for lung tumors. The aim of this study was to develop 4D radiotherapy treatment‐planning methodology for DMLC‐based respiratory motion tracking. A 4D computed tomography (CT) scan consisting of a series of eight 3D CT image sets acquired at different respiratory phases was used for treatment planning. Deformable image registration was performed to map each CT set from the peak‐inhale respiration phase to the CT image sets corresponding to subsequent respiration phases. Deformable registration allows the contours defined on the peak‐inhale CT to be automatically transferred to the other respiratory phase CT image sets. Treatment planning was simultaneously performed on each of the eight 3D image sets via automated scripts in which the MLC‐defined beam aperture conforms to the PTV (which in this case equaled the GTV due to CT scan length limitations) plus a penumbral margin at each respiratory phase. The dose distribution from each respiratory phase CT image set was mapped back to the peak‐inhale CT image set for analysis. The treatment intent of 4D planning is that the radiation beam defined by the DMLC tracks the respiration‐induced target motion based on a feedback loop including the respiration signal to a real‐time MLC controller. Deformation with respiration was observed for the lung tumor and normal tissues. This deformation was verified by examining the mapping of high contrast objects, such as the lungs and cord, between image sets. For the test case, dosimetric reductions for the cord, heart, and lungs were found for 4D planning compared with 3D planning. 4D radiotherapy planning for DMLC‐based respiratory motion tracking is feasible and may offer tumor dose escalation and/or a reduction in treatment‐related complications. However, 4D planning requires new planning tools, such as deformable registration and automated treatment planning on multiple CT image sets.
Retrospective analysis of 2D patient‐specific IMRT verifications
Authors: Childress Nathan L. , White R. Allen , Bloch Charles , Salehpour Mohammad , Dong Lei , Rosen Isaac I.
Published: April 2005

We performed 858 two‐dimensional (2D) patient‐specific intensity modulated radiotherapy verifications over a period of . Multifield, composite treatment plans were measured in phantom using calibrated Kodak EDR2 film and compared with the calculated dose extracted from two treatment planning systems. This research summarizes our findings using the normalized agreement test (NAT) index and the percent of pixels failing the gamma index as metrics to represent the agreement between measured and computed dose distributions. An in‐house dose comparison software package was used to register and compare all verifications. We found it was important to use an automatic positioning algorithm to achieve maximum registration accuracy, and that our automatic algorithm agreed well with anticipated results from known phantom geometries. We also measured absolute dose for each case using an ion chamber. Because the computed distributions agreed with ion chamber measurements better than the EDR2 film doses, we normalized EDR2 data to the computed distributions. The distributions of both the NAT indices and the percentage of pixels failing the gamma index were found to be exponential distributions. We continue to use both the NAT index and percent of pixels failing gamma with criteria to evaluate future verifications, as these two metrics were found to be complementary. Our data showed that using or criteria produces results similar to those using criteria. Normalized comparisons that have a NAT index greater than 45 and/or more than 20% of the pixels failing gamma for criteria represent outliers from our clinical data set and require further analysis. Because our QA verification results were exponentially distributed, rather than a tight grouping of similar results, we continue to perform patient‐specific QA in order to identify and correct outliers in our verifications. The data from this work could be useful as a reference for other clinics to indicate anticipated trends in 2D verifications under various conditions.
A stochastic convolution/superposition method with isocenter sampling to evaluate intrafraction motion effects in IMRT
Authors: Naqvi Shahid A. , D'Souza Warren D.
Published: April 2005

Current methods to calculate dose distributions with organ motion can be broadly classified as “dose convolution” and “fluence convolution” methods. In the former, a static dose distribution is convolved with the probability distribution function (PDF) that characterizes the motion. However, artifacts are produced near the surface and around inhomogeneities because the method assumes shift invariance. Fluence convolution avoids these artifacts by convolving the PDF with the incident fluence instead of the patient dose. In this paper we present an alternative method that improves the accuracy, generality as well as the speed of dose calculation with organ motion. The algorithm starts by sampling an isocenter point from a parametrically defined space curve corresponding to the patient‐specific motion trajectory. Then a photon is sampled in the linac head and propagated through the three‐dimensional (3‐D) collimator structure corresponding to a particular MLC segment chosen randomly from the planned IMRT leaf sequence. The photon is then made to interact at a point in the CT‐based simulation phantom. Randomly sampled monoenergetic kernel rays issued from this point are then made to deposit energy in the voxels. Our method explicitly accounts for MLC‐specific effects (spectral hardening, tongue‐and‐groove, head scatter) as well as changes in SSD with isocentric displacement, assuming that the body moves rigidly with the isocenter. Since the positions are randomly sampled from a continuum, there is no motion discretization, and the computation takes no more time than a static calculation. To validate our method, we obtained ten separate film measurements of an IMRT plan delivered on a phantom moving sinusoidally, with each fraction starting with a random phase. For 2 cm motion amplitude, we found that a ten‐fraction average of the film measurements gave an agreement with the calculated infinite fraction average to within 2 mm in the isodose curves. The results also corroborate the existing notion that the interfraction dose variability due to the interplay between the MLC motion and breathing motion averages out over typical multifraction treatments. Simulation with motion waveforms more representative of real breathing indicate that the motion can produce penumbral spreading asymmetric about the static dose distributions. Such calculations can help a clinician decide to use, for example, a larger margin in the superior direction than in the inferior direction. In the paper we demonstrate that a 15 min run on a single CPU can readily illustrate the effect of a patient‐specific breathing waveform, and can guide the physician in making informed decisions about margin expansion and dose escalation.
Reduction of eye lens radiation dose by orbital bismuth shielding in pediatric patients undergoing CT of the head: A Monte Carlo study
Authors: Perisinakis Kostas , Raissaki Maria , Tzedakis Antonis , Theocharopoulos Nicholas , Damilakis John , Gourtsoyiannis Nicholas
Published: April 2005

Our aim in the study was to assess the eye lens dose reduction resulting from the use of radioprotective bismuth garments to shield the eyes of pediatric patients undergoing head CT. The Monte Carlo ‐particle transport code and mathematical humanoid phantoms representing the average individual at different ages were used to determine eye lens dose reduction accomplished with bismuth shielding of the eye in the following simulated CT scans: (a) scanning of the orbits, (b) scanning of the whole head, and (c) 20° angled scanning of the brain excluding the orbits. The effect of bismuth shielding on the eye lens dose was also investigated using an anthropomorphic phantom and thermoluminescence dosimetry (TLD). Eye lens dose reduction achieved by bismuth shielding was measured in 16 patients undergoing multiphase CT scanning of the head. The patient's scans were divided in the following: CT examinations where the eye globes were entirely included , partly included and excluded from the scanned region. The eye lens dose reduction depended mainly on the scan boundaries set by an operator. The average eye lens dose reduction determined by Monte Carlo simulation was 38.2%, 33.0% and for CT scans of the orbits, whole head, and brain with an angled gantry, respectively. The difference between the Monte Carlo derived eye lens dose reduction factor values and corresponding values determined directly by using the anthropomorphic phantom head was found less than 5%. The mean eye lens dose reduction achieved by bismuth shielding in pediatric patients were 34%, 20% and when eye globes were entirely included, partly included and excluded from the scanned region, respectively. A significant reduction in eye lens dose may be achieved by using superficial orbital bismuth shielding during pediatric head CT scans. However, bismuth garments should not be used in children when the eyes are excluded from the primarily exposed region.
Low dose fraction behavior of high sensitivity radiochromic film
Authors: Hirata E. Y. , Cunningham C. , Micka J. A. , Keller H. , Kissick M. W. , DeWerd L. A.
Published: April 2005

A high sensitivity (HS) model of radiochromic film is receiving increasing use. The film's linear sensitometric response in the range of 0.5–40 Gy would make this film an ideal candidate for complex dosimetry applications that require tissue equivalence. This study investigates the potential use for clinical dosimetry of typical radiotherapy fractions at relatively low doses (0.5–5 Gy). The experiment involved exposing 25 pre‐exposed pieces of HS film to five equal fractions of doses from 0.5 to 5 Gy 24 hours apart. The cumulative dose for each film was carefully monitored and optical density measurements were used as the sole determination of film response to dose. The average behavior of the various fractionation schemes was roughly consistent with previous observations of the MD‐55 radiochromic film with about twice the overall sensitivity as expected. However, at low doses and low dose increments, unexpected variations beyond a well‐documented low dose nonlinearity were observed. These unexpected variations may indicate complex polymer kinetics at low doses. This type of film would require extra care beyond that described in TG‐55 for accurate use at low doses or low dose fraction schemes.
Identification of the Gene Encoding a 38-Kilodalton Immunogenic and Protective Antigen of
Streptococcus suis
Authors: Okwumabua Ogi , Chinnapapakkagari Sharmila
Published: April 2005

In our continued effort to search for a
Streptococcus suis
protein(s) that can serve as a vaccine candidate or a diagnostic reagent, we constructed and screened a gene library with a polyclonal antibody raised against the whole-cell protein of
S. suis
type 2. A clone that reacted with the antibody was identified and characterized. Analysis revealed that the gene encoding the protein is localized within a 2.0-kbp EcoRI DNA fragment. The nucleotide sequence contained an open reading frame that encoded a polypeptide of 445 amino acid residues with a calculated molecular mass of 46.4 kDa. By in vitro protein synthesis and Western blot experiments, the protein exhibited an electrophoretic mobility of approximately 38 kDa. At the amino acid level the deduced primary sequence shared homology with sequences of unknown function from
Streptococcus pneumoniae
(89%),
Streptococcus mutans
(86%),
Lactococcus lactis
(80%),
Listeria monocytogenes
(74%), and
Clostridium perfringens
(64%). Except for strains of serotypes 20, 26, 32, and 33, Southern hybridization analysis revealed the presence of the gene in strains of other
S. suis
serotypes and demonstrated restriction fragment length differences caused by a point mutation in the EcoRI recognition sequence. We confirmed expression of the 38-kDa protein in the hybridization-positive isolates using specific antiserum against the purified protein. The recombinant protein was reactive with serum from pigs experimentally infected with virulent strains of
S. suis
type 2, suggesting that the protein is immunogenic and may serve as an antigen of diagnostic importance for the detection of most
S. suis
infections. Pigs immunized with the recombinant 38-kDa protein mounted antibody responses to the protein and were completely protected against challenge with a strain of a homologous serotype, the wild-type virulent strain of
S. suis
type 2, suggesting that it may be a good candidate for the development of a vaccine that can be used as protection against
S. suis
infection. Analysis of the cellular fractions of the bacterium by Western blotting revealed that the protein was present in the surface and cell wall extracts. The functional role of the protein with respect to pathogenesis and whether antibodies against the antigen confer protective immunity against diseases caused by strains of other pathogenic
S. suis
capsular types remains to be determined.
Point Seroprevalence Survey ofEhrlichia ruminantiumInfection in Small Ruminants in The Gambia
Authors: Faburay Bonto , Munstermann Susanne , Geysen Dirk , Bell-Sakyi Lesley , Ceesay Ansumana , Bodaan Christa , Jongejan Frans
Published: April 2005

Using the MAP1-B enzyme-linked immunosorbent assay, we tested 1,318 serum samples collected from sheep and goats at 28 sites in the five divisions of The Gambia to determine theEhrlichia ruminantiumseroprevalence rates and to assess the risk for heartwater. About half (51.6%) of 639 sheep were positive, with seroprevalence rates per site varying between 6.9% and 100%. The highest seroprevalence was detected in the western part of the country (88.1% in the Western Division and 62.1% in the Lower River Division). Sheep in the two easterly divisions (Central River and Upper River divisions) showed the lowest seroprevalence of 29.3% and 32.4%, respectively, while those in the North Bank Division showed an intermediate prevalence of 40.6%. In goats, less than one-third (30.3%) of 679 animals tested were positive. The highest seroprevalence was detected in goats in the North Bank Division (59%) and Western Division (44.1%). Goats in the Lower River Division showed an intermediate level of 21.9%, whereas the lowest rates were found in the eastern part of the country (4.8% in the Central River Division and 2.3% in the Upper River Division). At nearly all sites, seroprevalence rates were higher in sheep than in goats. The results show a gradient of increasing heartwater risk for susceptible small ruminants from the east to the west of The Gambia. These findings need to be taken into consideration when future livestock-upgrading programs are implemented.
Simultaneous Serodetection of 10 Highly Prevalent Mouse Infectious Pathogens in a Single Reaction by Multiplex Analysis
Authors: Khan Imran H. , Kendall Lon V. , Ziman Melanie , Wong Scott , Mendoza Sara , Fahey James , Griffey Stephen M. , Barthold Stephen W. , Luciw Paul A.
Published: April 2005

Under current practices of mouse colony maintenance, sera from mice are analyzed for antibodies against several widespread infectious pathogens by conventional immunoassays, generally enzyme-linked immunosorbent assay (ELISA). To test for multiple agents, these methods consume large volumes of mouse serum and are laborious and time-consuming. More efficient immunoassays, using small amounts of sample, are therefore needed. Accordingly, we have developed a novel multiplex diagnostic system that employs fluorescent microbeads, coated with purified antigens, for simultaneous serodetection of 10 mouse infectious agents. Individually identifiable, fluorescent microbeads were coated with antigens from Sendai virus, mouse hepatitis virus, Theiler's mouse encephalomyelitis virus/GDVII strain, mouse minute virus, mouse cytomegalovirus, respiratory enteric orphan virus (Reo-3 virus), mouse parvovirus, calf rotavirus for epizootic diarrhea virus of infant mice, vaccinia virus for ectromelia virus, and
Mycoplasma pulmonis
. Standard sera, singly positive for antibodies to individual infectious agents, were generated by inoculation of BALB/cj and C57BL/6j mice. Sera from these experimentally infected mice, as well as sera from naturally infected mice, were analyzed using a mixture of microbeads coated with antigens of the 10 infectious agents listed above. Results demonstrated that the multiplex assay was at least as sensitive and specific as ELISA for serodetection. Importantly, the multiplex assay required only 1 microliter of serum for simultaneous serodetection of the 10 mouse infectious agents in one reaction vessel. Thus, this multiplex microbead assay is a reliable, efficient, and cost-effective diagnostic modality that will impact serosurveillance of mice used in research.