bluuebunny/crossref_metadata_2025 huggingface dataset:
Cross-presentation of Disialoganglioside GD3 to Natural Killer T Cells
Authors: Wu Dianna Y. , Segal Neil H. , Sidobre Stephane , Kronenberg Mitchell , Chapman Paul B.
Published: July 2003

GD3, a ganglioside expressed on human melanoma, can be recognized by the humoral immune system. In this paper, we demonstrate that immunizing mice with the human melanoma cell line SK-MEL-28 (GD3+ GM2− CD1−) or with syngeneic APCs loaded with GD3 can induce a GD3-reactive natural killer T (NKT) cell response. GD3-reactive NKT cells were detected among splenocytes of immunized mice at frequencies of ∼1:2,000 both by ELISPOT and GD3-loaded mouse CD1d tetramer analysis. GD3-reactive NKT cells did not react with GM2, a closely related ganglioside, and were not detectable in unimmunized mice. GD3-reactive NKT cells initially produced IL-4 and IFN-γ followed by IL-10. They were CD1d restricted in that reactivity was abrogated when APCs were blocked with anti-CD1d monoclonal antibody before being loaded with GD3 or when APCs from CD1d knockout mice were used. Because SK-MEL-28 does not express any isoform of human CD1, GD3 must be cross-presented by murine APCs in vivo. This is the first analysis of a natural ligand for mouse NKT cells and the first definitive paper of cross-presentation to NKT cells. This could be a mechanism for NKT cell recognition of tumor gangliosides in CD1− tumors.
Co‐creating change within a child protection system: integrating art therapy with family therapy practice
Authors: Manicom Hilary , Boronska Teresa
Published: July 2003

This paper considers family art therapy intervention using a partnership developed between an art therapist and a family therapist within a child protection system. The aim of this co‐working relationship is to bring together skills that can amplify the child's voice within the family, using art as a means of extending the family story. The use of metaphor adds to the repertoire of skills available when working with families, and offers a particular form of communication in which children can more easily engage. By co‐working, we also bring together our personal and professional stories, creating multiple ideas and ways of seeing and taking account of differences in the life experiences of individual families.
Systemic family therapy can be manualized: research process and findings
Authors: Pote H. , Stratton P. , Cottrell D. , Shapiro D. , Boston P.
Published: July 2003

Determining the efficacy of therapeutic interventions is becoming an increasing political and ethical necessity. Comparative therapeutic outcome trials are most powerful when there is a precise specification, or manualization, of the forms that therapies took. Manuals have begun to be developed for structural/behavioural family therapy and couple therapy. The development of these manuals is often reliant on experts' self‐report, rather than a systematic analysis of the therapeutic process as it happens. This can limit their validity and applicability to standard clinical practice. In addition, no manuals exist which reflect less structured forms of family therapy aimed at incorporating systemic, postmodern and narrative frameworks. The feasibility of producing a workable manual that reflects the fluidity of such practices has been questioned.

A research project to systematically create and test such a manual is reported. Multiple data sources and research methods, primarily qualitative, were applied to generate a rich specification of the therapy. In reporting these results the contents of various aspects of the final manual are indicated. Procedures to ensure that the prescribed practice is consistent with a widely used approach to systemic family therapy are also described.

The manual will be an important tool for outcome research and therapeutic practice. The account of the research process should be helpful to researchers engaged in constructing a manual for other models of family therapy based on a rigorous analysis of actual practice. The manual itself is available for use by outcome researchers who wish to evaluate this widely used form of systemic family therapy.
What the family brings: gathering evidence for strengths‐based work
Authors: Allison Steve , Stacey Kathleen , Dadds Vicki , Roeger Leigh , Wood Andrew , Martin Graham
Published: July 2003

Families attending child and adolescent mental health (CAMH) services are often assumed to have problems in key areas such as communication, belonging/acceptance and problem‐solving. Family therapy is often directed towards addressing these difficulties. With increasing emphasis in family therapy and human services fields over the last decade on identifying and building from strengths, a different starting point has been advocated. This paper describes a large survey of the self‐reported pre‐therapy functioning of children and families using a public CAMH service (n=416). Before commencing family therapy parents identified family strengths across a range of key areas, despite the burden of caring for children with moderate to severe mental health problems. This evidence supports theoretical and clinical work that advocates a strengths perspective, and highlights how resilience framed in family (and social) rather than individual terms enables a greater appreciation of how strengths may be harnessed in therapeutic work.
Family therapy beyond postmodernism: some considerations on the ethical orientation of contemporary practice
Authors: Donovan Mary
Published: July 2003

Ethics is a subject that is self‐evidently important for systemic therapy, as for therapy generally, yet arguably it is one that has not received nearly as much attention in the literature as it warrants. This paper looks at the historical context for the marginalization of ethical discourse and suggests that the contemporary influence of postmodernist and hermeneutic thinking reinforces this tendency. Flaskas’ (2002) recent argument for the reclamation of an idea of truth and reality as a social and emotional process is considered, and it is suggested that this needs supplementing with a perspective on truth and reality as an ethical process. Consideration is given to the enduring influence within postmodernist approaches of the modernist Kantian conception of ethics as centred in individual consciousness. I argue that important elements of contemporary systemic practice (for example, the reflecting team approach) are also pointing towards a different formulation of ethics that is focused more specifically on processes of communication. In elaborating this theme the paper draws on the work of the German social theorist Jürgen Habermas who writes on the ethics of communication.
Progressive Hulls for Intersection Applications
Authors: Platis Nikos , Theoharis Theoharis
Published: July 2003

Progressive meshes are an established tool for triangle mesh simplification. By suitably adapting the simplification process, progressive hulls can be generated which enclose the original mesh in gradually simpler, nested meshes. We couple progressive hulls with a selective refinement framework and use them in applications involving intersection queries on the mesh. We demonstrate that selectively refinable progressive hulls considerably speed up intersection queries by efficiently locating intersection points on the mesh. Concerning the progressive hull construction, we propose a new formula for assigning edge collapse priorities that significantly accelerates the simplification process, and enhance the existing algorithm with several conditions aimed at producing higher quality hulls. Using progressive hulls has the added advantage that they can be used instead of the enclosed object when a lower resolution of display can be tolerated, thus speeding up the rendering process.

ACM CSS: I.3.3 Computer Graphics—Picture/Image Generation, I.3.5 Computer Graphics—Computational Geometry and Object Modeling, I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism
Recent Developments and Applications of Haptic Devices
Authors: Laycock S. D. , Day A. M.
Published: July 2003

Over recent years a variety of haptic feedback devices have been developed and are being used in a number of important applications. They range from joysticks used in the entertainment industry to specialised devices used in medical applications. This paper will describe the recent developments of these devices and show how they have been applied. It also examines how haptic feedback has been combined with visual display devices, such as virtual reality walls and workbenches, in order to improve the immersive experience.

ACM CSS: H.5.2 Information Interfaces and Presentation—Haptic I/O; I.3.8 Computer Graphics—Applications; I.6 Simulation and Modelling—Applications
Local Exact Particle Tracing on Unstructured Grids
Authors: Kipfer Peter , Reck Frank , Greiner Günther
Published: July 2003

For analyzing and interpreting results of flow simulations, particle tracing is a well established visualization method. In addition, it is a preliminary step for more advanced techniques such as line integral convolution. For interactive exploration of large data sets, a very efficient and reliable particle tracing method is needed. For wind channel experiments or flight simulations, large unstructured computational grids have become common practice. Traditional approachs, based on numerical integration methods of ordinary differential equations however fail to deliver sufficiently accurate path calculation at the speed required for interactive use. In this paper we extend the local exact approach of Nielson and Jung in such a way that it can be used for interactive particle tracing in large data sets of steady flow simulation experiments. This will be achieved by sophisticated preprocessing using additional memory. For further visual enhancement of the streamline we construct an implicitly defined smooth Bézier curve that is used for ray tracing. This allows us to visualize additional scalar values of the simulation as attributes to the trajectory and enables the display of high‐quality smooth curves without creating any visualization geometry and providing a good impression of the spatial situation at the same time.

ACM CSS: I.3.3 Computer Graphics—Line and curve generation; I .3.7 Computer Graphics—Raytracing; G.1.2 Numerical Analysis—Spline and piecewise polynomial approximation
The Scale Method for Blending Operations in Functionally‐Based Constructive Geometry
Authors: Hsu P.‐C. , Lee C.
Published: July 2003

This paper presents a scale method for developing high dimensional scale functions to blend implicitly defined objects. Scale functions are differentiable on the entire domain except the origin, provide blending range control, and behave like Min/Max operators everywhere, so even a successive composition of blending operations containing overlapped blending regions can be generated smoothly. Because the scale method is a generalized method, implicit or parametric curves, such as cubic Bezier curves, rational conic curves, and implicit conics and hyper‐ellipsoids, can be used to develop scale functions. As a result, it can enhance the flexibility of generating the implicitly blending surfaces in Ricci's constructive geometry, soft objects modeling, and implicit sweep objects.

ACM CSS: I.3.5 Computer Graphics—Computational Geometry and Object Modeling ‐ Curve, surface, solid and object representations
Approximating Parametric Curves With Strip Trees Using Affine Arithmetic
Authors: Henrique de Figueiredo Luiz , Stolfi Jorge , Velho Luiz
Published: July 2003

We show how to use affine arithmetic to represent a parametric curve with a strip tree. The required bounding rectangles for pieces of the curve are computed by exploiting the linear correlation information given by affine arithmetic. As an application, we show how to compute approximate distance fields for parametric curves.

ACM CSS: I.3.3 Computer Graphics—Curve, surface, solid, and object representations, G.1.2 Numerical Analysis—Approximation of surfaces and contours, G.1.0 Numerical Analysis—Interval arithmetic
3D Video Recorder: a System for Recording and Playing Free‐Viewpoint Video†
Authors: Würmlin Stephan , Lamboray Edouard , Staadt Oliver G. , Gross Markus H.
Published: July 2003

We present the 3D Video Recorder, a system capable of recording, processing, and playing three‐dimensional video from multiple points of view. We first record 2D video streams from several synchronized digital video cameras and store pre‐processed images to disk. An off‐line processing stage converts these images into a time‐varying 3D hierarchical point‐based data structure and stores this 3D video to disk. We show how we can trade‐off 3D video quality with processing performance and devise efficient compression and coding schemes for our novel 3D video representation. A typical sequence is encoded at less than 7 Mbps at a frame rate of 8.5 frames per second. The 3D video player decodes and renders 3D videos from hard‐disk in real‐time, providing interaction features known from common video cassette recorders, like variable‐speed forward and reverse, and slow motion. 3D video playback can be enhanced with novel 3D video effects such as freeze‐and‐rotate and arbitrary scaling. The player builds upon point‐based rendering techniques and is thus capable of rendering high‐quality images in real‐time. Finally, we demonstrate the 3D Video Recorder on multiple real‐life video sequences.

ACM CSS: I.3.2 Computer Graphics—Graphics Systems, I.3.5 Computer Graphics—Computational Geometry and Object Modelling, I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism
Interactive Rendering of Translucent Objects†
Authors: Lensch Hendrik P.A. , Goesele Michael , Bekaert Philippe , Kautz Jan , Magnor Marcus A. , Lang Jochen , Seidel Hans‐Peter
Published: July 2003

This paper presents a rendering method for translucent objects, in which viewpoint and illumination can be modified at interactive rates. In a preprocessing step, the impulse response to incoming light impinging at each surface point is computed and stored in two different ways: The local effect on close‐by surface points is modeled as a per‐texel filter kernel that is applied to a texture map representing the incident illumination. The global response (i.e. light shining through the object) is stored as vertex‐to‐vertex throughput factors for the triangle mesh of the object. During rendering, the illumination map for the object is computed according to the current lighting situation and then filtered by the precomputed kernels. The illumination map is also used to derive the incident illumination on the vertices which is distributed via the vertex‐to‐vertex throughput factors to the other vertices. The final image is obtained by combining the local and global response. We demonstrate the performance of our method for several models.

ACM CSS:I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism Color Radiosity
Real‐Time Consensus‐Based Scene Reconstruction Using Commodity Graphics Hardware†
Authors: Yang Ruigang , Welch Greg , Bishop Gary
Published: July 2003

We present a novel use of commodity graphics hardware that effectively combines a plane‐sweeping algorithm with view synthesis for real‐time, online 3D scene acquisition and view synthesis. Using real‐time imagery from a few calibrated cameras, our method can generate new images from nearby viewpoints, estimate a dense depth map from the current viewpoint, or create a textured triangular mesh. We can do each of these without any prior geometric information or requiring any user interaction, in real time and online. The heart of our method is to use programmable Pixel Shader technology to square intensity differences between reference image pixels, and then to choose final colors (or depths) that correspond to the minimum difference, i.e. the most consistent color. In this paper we describe the method, place it in the context of related work in computer graphics and computer vision, and present some results.

ACM CSS: I.3.3 Computer Graphics—Bitmap and framebuffer operations, I.4.8 Image Processing and Computer Vision—Depth cues, Stereo
Elizabeth I as a Second Virgin Mary
Authors: McClure Peter , Wells Robin Headlam
Published: July 2003

Elizabethan poets and panegyrists found images of glorious, powerful virgins to exalt their queen in both classical literature – especially the Virgilian figure of Astraea – and Christian tradition. An examination of literature, drama, and the visual arts reveals substantial use of imagery traditionally used to describe the Virgin Mary: virgin mother, bride, and queen; the flower of the Tree of Jesse, merciful intercessor, walled garden, thornless rose. An Elizabethan cult imitated and replaced Marian devotion. This association and substitution provided Elizabethan propagandists and their audience with compelling ways to express, enhance, and justify the queen's authority and identity and her relations with her kingdom, her church, and the world beyond her realm.
Leonardo Da Vinci, the Hayward Gallery, London, 26 January‐16 April 1969
Authors: Rubin Patricia
Published: July 2003

Reviews an exhibition of the drawings of Leonardo da Vinci at the Hayward Gallery, London, that presents Leonardo as artist, scientist, and inventor and attempts to reveal his characteristic ways of seeing and patterns of creativity.
An Efficient Geometric Algorithm For Extracting Structural Elements to Facilitate Automated MEMS Extraction
Authors: Bellam and S. , Gupta S. K.
Published: July 2003

Micro-electro-mechanical systems (MEMS) are very small devices that contain both mechanical and electrical elements with sizes in the order of microns. Design cycle time is an important consideration in the development and introduction of MEMS devices in the market. To develop extraction tools for MEMS designs, we need geometric algorithms to analyze the spatial layout of the mechanical portion of the MEMS device and extract a net-list of mechanical components. Such extracted net-list of mechanical components can be combined with the electronic component net-list to provide the complete device schematic. A key step in the extraction of mechanical elements is classification of various portions of the layout into structural elements. Because MEMS designs consist of a large number of elements, computational efficiency of the underlying extraction algorithm is very important for it to work on complex devices. This paper describes an efficient geometric algorithm for extracting structural elements from spatial layout of MEMS designs.
Weight Sensation in Virtual Environments Using a Haptic Device With Air Jets
Authors: Gurocak Hakan , Jayaram , Sankar , Parrish , and Benjamin , Jayaram Uma
Published: July 2003

The research presented in this paper is the design and implementation of a force feedback hand master called AirGlove. The device uses six ports arranged in a Cartesian coordinate frame setting to apply a point force to the user’s hand. Compressed air is exhausted through the ports, creating thrust forces. The magnitude and direction of the resultant force are controlled by changing the flow rate of the air jets and by activating different ports. The AirGlove can apply an arbitrary point force to the user’s hand. However, the main goal of this research is to reflect gravitational forces to the user so that sensation of weight of a virtual object can be created. After introduction of the main concept of the AirGlove, the paper presents design and implementation details of the device. Integration of the AirGlove with a virtual assembly system called VADE is explained next. Finally, details of experiments with the device are presented and discussed. Results indicate that users wearing the AirGlove can feel a minimum mass of about 100 grams (∼1N weight) and the device can create a fairly realistic weight sensation.
Improved Display Methods of Single-valued Functions of Two Variables
Authors: Simionescu P. A.
Published: July 2003

Based on the depth-sorting hidden-line removal algorithm, new methods of producing silhouette and raised level-curve diagrams with the hidden-lines removed of single-valued functions of two variables are presented. An algorithm of generating accurate truncated representations over the z-axis of the same types of functions is also described. These methods are particularly advantageous when plotting multimodal functions, noisy data or penalized objective functions encountered in optimization problems. Since all the graphic operations are performed entirely in the 2D image-space, the methods presented are suitable for implementation in low memory hardware like hand-held calculators and field instruments.
A Survey of Shape Similarity Assessment Algorithms for Product Design and Manufacturing Applications
Authors: Cardone , Antonio , Gupta, Satyandra K. , Karnik Mukul
Published: July 2003

Shape similarity assessment is a fundamental geometric reasoning problem that finds application in several different product design and manufacturing applications. A computationally efficient way to assess shape similarity is to first abstract 3D object shapes into shape signatures and use shape signatures to perform similarity assessment. Several different types of shape signatures have been developed in the past. This paper provides a survey of existing algorithms for computing and comparing shape signatures. Our survey consists of a description of the desired properties of shape signatures, a scheme for classifying different types of shape signatures, and descriptions of representative algorithms for computing and comparing shape signatures. This survey concludes by identifying directions for future research.
Measuring the Effectiveness of Presence and Immersive Tendencies on the Conceptual Design Review Process
Authors: Banerjee Pat , Basu-Mallick Debraj
Published: July 2003

This is the second and final publication analyzing presence, immersive tendencies of individuals, and design comprehension. The effectiveness measurement problem is described in this article by means of a methodology to find the best design review process subject to certain criteria. The effectiveness measurement problem originates from our inability to logically understand the impact of a process or media differences on design comprehension; and it reconciles such differences in strengths of media that cannot be effectively covered by the relationship problem described in the first technical note. We illustrate the methodology with design review experiments where Computer Aided Virtual Environment (CAVE™2) is investigated as a possible virtual environment for product design reviews. Based on the measurable usability attributes of the design review process, the CAVE was considered to be a good solution achieving maximum utility. However, costs may hinder the ability to use CAVE as a tool.
CADDAC: Multi-Client Collaborative Shape Design System with Server-based Geometry Kernel
Authors: Ramani, Karthik , Agrawal, and Abhishek , Babu Mahendra , Hoffmann Christoph
Published: July 2003

New and efficient paradigms for web-based collaborative product design in a global economy will be driven by increased outsourcing, increased competition, and pressures to reduce product development time. We have developed a three-tier (client-server-database) architecture based collaborative shape design system, Computer Aided Distributed Design and Collaboration (CADDAC). CADDAC has a centralized geometry kernel and constraint solver. The server-side provides support for solid modeling, constraint solving operations, data management, and synchronization of clients. The client-side performs real-time creation, modification, and deletion of geometry over the network. In order to keep the clients thin, many computationally intensive operations are performed at the server. Only the graphics rendering pipeline operations are performed at the client-side. A key contribution of this work is a flexible architecture that decouples Application Data (Model), Controllers, Viewers, and Collaboration. This decoupling allows new feature development to be modular and easy to develop and manage.
Assessing the Impact of Graphical Design Interfaces on Design Efficiency and Effectiveness
Authors: Ligetti Christopher , Simpson Timothy W. , Frecker Mary , Barton Russell R. , Stump Gary
Published: July 2003

Despite the apparent advantages of and recent advances in the use of visualization in engineering design and optimization, we have found little evidence in the engineering literature that assesses the impact of fast, graphical design interfaces on the efficiency and effectiveness of engineering design decisions or the design optimization process. In this paper we discuss two examples—the design of an I-beam and the design of a desk lamp—for which we have developed graphical and text-based design interfaces to assess the impact of having fast graphical feedback on design efficiency and effectiveness. Design efficiency is measured by recording the completion time for each design task, and design effectiveness is measured by calculating the error between each submitted design and the known optimal design. The impact of graphical feedback is examined by comparing user performance on the graphical and text-based design interfaces while the importance of rapid feedback is investigated by comparing user performance when response delays are introduced within each design interface. Experimental results indicate that users of graphical design interfaces perform better (i.e., have lower error and faster completion time) on average than those using text-based design interfaces, but these differences are not statistically significant. Likewise, we found that a response delay of 0.5 seconds increases error and task completion time, on average, but these increases are not always statistically significant. Trials using longer delays of 1.5 seconds did yield significant increases in task completion time. We also found that the perceived difficulty of the design task and using the graphical interface controls were inversely correlated with design effectiveness—designers who rated the task more difficult to solve or the graphical interface more difficult to use actually performed better than those who rated them easy. Finally, a significant “playing” effect was observed in our experiments: those who played video games more frequently or rated the slider bars and zoom controls easy to use took more time to complete the design tasks.
On site evaluation of three flat panel detectors for digital radiography
Authors: Borasi Giovanni , Nitrosi Andrea , Ferrari Paolo , Tassoni Davide
Published: July 2003

During a tender we evaluated the image performance of three commercially available active matrix flat panel imagers (AMFPI) for general radiography, one based on direct detection method (Se photoconductor) the other two on indirect detection method (CsI phosphor). Basic image quality parameters (MTF, NNPS, DQE) were evaluated with particular attention to dose and energy dependence. As it is known, presampling modulation transfer function (MTF) of selenium based detector is very high (at 70 kV, 2 cycles/mm, 2.5 μGy, about 0.80). Indirect detection panels exhibit a comparable (lower) resolution (at 70 kV, 2 cycles/mm, 2.5 μGy, MTF is about 0.34 for both the systems analyzed) and a more pronounced energy and dose dependence could also be noted in one of them. As a consequence of the very high resolution, the normalized noise power spectrum (NNPS) of the direct system is substantially flat, very similar to a white noise. Considering that the sensitive layer of all detectors is the same (0.5 mm), the relatively higher NNPS values are related to selenium absorption properties (lower Z respect to CsI:Tl) and detector inherent noise. NNPSs of the other systems, at low frequencies, are comparable but the frequency dependence is significantly different. At 70 kV, 2.5 μGy, 0.5 cycles/mm detective quantum efficiency (DQE) is about 0.35 for the direct detection system, and about the same (0.6) for the indirect ones. The combined effect of additive and multiplicative noise components makes DQE dependence on dose not monotonic. DQE present a maximum for an intermediate exposure. This complex behavior may be useful to characterize the systems in terms of the monodimensional integral over the frequency of DQE (IDQE). Both visual contrast‐detail experiment and the direct evaluation of the signal‐to‐noise ratio confirmed, at least in a qualitative way, the system performances predicted by IDQE.
Development and application of efficient portal imaging solutions
Authors: de Boer J. C. J.
Published: July 2003

This thesis describes the theoretical derivation and clinical application of methods to measure and improve patient setup in radiotherapy by means of electronic portal imaging devices (EPIDs). The focus is on methods that (1) are simple to implement and (2) add minimal workload. First, the relation between setup errors and treatment planning margins is quantified in a population‐statistics approach. A major result is that systematic errors (recurring each treatment fraction) require about three times larger margins than random errors (fluctuating from fraction to fraction). Therefore, the emphasis is on reduction of systematic setup errors using off‐line correction protocols. The new no action level (NAL) protocol, aimed at significant reduction of systematic errors using a small number of imaged fractions, is proposed and investigated in detail. It is demonstrated that the NAL protocol provides final distributions of residue systematic errors at least as good as the most widely applied comparable protocol, the shrinking action level (SAL) protocol, but uses only 3 imaged fractions per patient instead of the 8–10 required by SAL. The efficacy of NAL is demonstrated retrospectively on a database of measured setup errors involving 600 patients with weekly set‐up measurements and prospectively in a group of 30 patients. The general properties of NAL are investigated using both analytical and Monte Carlo calculations. As an add‐on to NAL, a correction verification (COVER) protocol has been developed using computer simulations combined with a risk analysis. With COVER, a single additional imaged fraction per patient is sufficient to reduce the detrimental effect of possible systematic mistakes in the execution of setup corrections to negligible levels. The high accuracy achieved with off‐line setup corrections (yielding SDs of systematic errors is demonstrated in clinical studies involving 60 lung cancer patients and 31 head‐and‐neck patients. Furthermore, potential problems arising from nonrigid body anatomy are quantified in large cervix treatment fields. Finally, the suitability of our in‐house developed (and currently commercially available) CCD‐camera‐based EPID for portal dosimetry is described. An algorithm is developed to transform EPID images into accurate dose images (SD of dose based on fundamental properties of the EPID.
Thermoluminescent dosimetry of the SourceTech Medical model STM1251 seed
Authors: Chiu‐Tsao Sou‐Tung , Duckworth Tamara L. , Hsiung Chih‐Yun , Li Zuofeng , Williamson Jeffrey , Patel Neil S. , Harrison Louis B.
Published: July 2003

Many new models of seeds are being introduced, mainly due to the increase in prostate seed implants. We have evaluated the SourceTech Medical (STM), model STM1251, seed using thermoluminescent dosimeters (TLDs) in a solid water phantom. TLD cubes, LiF TLD‐100, with dimension 1 mm on each edge, were irradiated at various distances, 1, 2, 3, and 5 cm, at angles ranging from 0° to 90° in 10° increments. Sensitivity calibration of the TLDs was achieved by irradiation to 10 cGy with 6 MV x rays from a clinical linear accelerator, Clinac 600C. Concurrent with the seed exposures, several TLDs were also exposed to 10 cGy with the 600C as a control set. Dose rates per unit air kerma strength were determined based on the 1999 NIST traceable standard for the STM1251 seed. They are presented as a function of distance r and angle θ. The TG‐43 parameters, including the dose rate constant, Λ, anisotropy function, radial dose function, anisotropy factor, and anisotropy constant, were obtained for use in radiation treatment planning software. The value of Λ was determined as 1.07±5.5% cGy which is comparable to model 6702 and to the value determined using the point extrapolation method by Kirov and Williamson. We also find agreement between our TLD data and their Monte Carlo results for and φ. Additionally, agreement is found with the TLD data of Li and Williamson for Λ and
Effect of ethmoid sinus cavity on dose distribution at interface and how to correct for it: Magnetic field with photon beams
Authors: Wadi‐Ramahi Shada J. , Bernard Damian , Chu James C. H.
Published: July 2003

Recent work proposed the use of magnetic field as a solution to reduce the undesirable effect of air cavities on dose after the air/tissue interface. In contrast to the published work that looks into the problem with slab geometries, in this work we use actual anatomy based on CT images and the magnetic flux from a Helmholtz coil‐pair configuration to investigate the problem and to evaluate the efficacy of the proposed solution. The EGS4 phantom was created using CT scans of the head at the level of the ethmoid sinus. The sinus measures 1.95×2.18×2.00 cm3. The grid size used is 0.15×0.15×0.4 cm3. Three different radiation beams, 1×1, 2×2, and 4×4 cm2, all 6 MV irradiate the phantom in two different configurations: single beam and parallel opposed. The magnetic field has three different strengths: 0.0, 0.5, and 1.0 T. These represent the maximum strength achieved in the middle of the configuration, between the two coils. The depth of the second buildup region in the absence of the magnetic field was used as the normalization point for the purpose of analysis. Dose was then scored at 0.23 cm after the air/tissue interface. A second phantom, very similar to the CT‐based phantom, was created, but with the sinus cavity filled with unit‐density tissue; everything else remained the same. This phantom provides a base to investigate the effect of the air cavity on dose. The phantom was termed the phantom without air, or PWA for short. We use the terms “dose reduction ratio” (DRR), defined as one minus the ratio of the dose in PWA to the dose with the presence of the cavity multiplied by 100% and the “dose improvement ratio” (DIR), defined as the ratio of dose with B to that without B, to evaluate the reduction in dose due to the cavity and the improvement in dose with magnetic field, respectively. For single beam geometry, the reduced dose ranged from 41% (1×1 cm2 beam) to less than 2% (4×4 cm2 beam). For the same single beam geometry, DIR ranged from 1.13 to 1.00 (DIR=1 indicates no change) with 0.5 T, whereas it ranged from 1.44 to 1.05 for 1.0 T magnets. When an opposing beam was used, the reduced dose was not as severe, such that DRR ranged from 24% to less than 2%. Whereas the dose improvement ranged from 1.08 to 1.00 for 0.5 T, and from 1.23 to 1.01 for 1.0 T.
The effects of intra‐fraction organ motion on the delivery of intensity‐modulated field with a multileaf collimator
Authors: Chui Chen‐Shou , Yorke Ellen , Hong Linda
Published: July 2003

Intensity‐modulated radiation therapy can be conveniently delivered with a multileaf collimator. With this method, the entire field is not delivered at once, but rather it is composed of many subfields defined by the leaf positions as a function of beam on time. At any given instant, only these subfields are delivered. During treatment, if the organ moves, part of the volume may move in or out of these subfields. Due to this interplay between organ motion and leaf motion the delivered dose may be different from what was planned. In this work, we present a method that calculates the effects of organ motion on delivered dose. The direction of organ motion may be parallel or perpendicular to the leaf motion, and the effect can be calculated for a single fraction or for multiple fractions. Three breast patients and four lung patients were included in this study, with the amplitude of the organ motion varying from to and the period varying from 4 to 8 seconds. Calculations were made for these patients with and without organ motion, and results were examined in terms of isodose distribution and dose volume histograms. Each calculation was repeated ten times in order to estimate the statistical uncertainties. For selected patients, calculations were also made with conventional treatment technique. The effects of organ motion on conventional techniques were compared relative to that on IMRT techniques. For breast treatment, the effect of organ motion primarily broadened the penumbra at the posterior field edge. The dose in the rest of the treatment volume was not significantly affected. For lung treatment, the effect also broadened the penumbra and degraded the coverage of the planning target volume (PTV). However, the coverage of the clinical target volume (CTV) was not much affected, provided the PTV margin was adequate. The same effects were observed for both IMRT and conventional treatment techniques. For the IMRT technique, the standard deviations of ten samples of a 30‐fraction calculation were very small for all patients, implying that over a typical treatment course of 30 fractions, the delivered dose was very close to the expected value. Hence, under typical clinical conditions, the effect of organ motion on delivered dose can be calculated without considering the interplay between the organ motion and the leaf motion. It can be calculated as the weighted average of the dose distribution without organ motion with the distribution of organ motion. Since the effects of organ motion on dose were comparable for both IMRT and conventional techniques, the PTV margin should remain the same for both techniques.
Image quality in two phosphor‐based flat panel digital radiographic detectors
Authors: Samei Ehsan
Published: July 2003

Two general types of phosphor screens are currently used in indirect digital radiographic systems: structured phosphor screens and turbid phosphor screens. The purpose of the study was to experimentally compare the image quality characteristics of two flat‐panel digital radiography detectors with similar electronics and pixel sizes (0.127 mm), but otherwise equipped with the two types of screens (0.6‐mm‐thick structured CsI and Lanex Regular). The presampled modulation transfer functions (MTFs) of the detectors were assessed using an edge method. The noise power spectra (NPS) were measured by two‐dimensional Fourier analysis of uniformly‐exposed radiographs at 50–100 kVp with 19 mm added Al filtration. The detective quantum efficiencies (DQEs) were assessed from the MTF, the NPS, and estimates of the ideal signal‐to‐noise ratio. The MTF measures of the two detectors were generally similar above a spatial frequency of 2 mm−1, with ∼2.5 and ∼3.8 mm−1 spatial frequencies corresponding to 0.2 MTF and 0.1 MTF, respectively. Below 2 mm−1, the MTF for the CsI‐based detector was slightly higher by an average of 0.07. At 70 kVp, the measured DQE values in the diagonal (and axial) direction(s) at spatial frequencies of 0.15 mm−1 and 2.5 mm−1 were 78% (78%) and 26% (20%) for the CsI‐based detector, and 20% (20%) and 7% (6%) for the Lanex‐based detector, respectively. The comparative findings experimentally confirm that in indirect flat‐panel detectors, structured phosphor screens provide a more favorable tradeoff between resolution and noise compared to turbid‐phosphor screens, effectively increasing the detection efficiency of the detector without a negative impact on the detector's spatial resolution response.
The design of a new insert for calibration of LDR and HDR sources in a well‐type ionization chamber
Authors: Pineda A. E. C. , Alcón E. P. Q. , deAlmeida C. E.
Published: July 2003

Some well‐type ionization chambers, present a very small sweet spot that are sufficient for small HDR sources. However, if a longer HDR source or LDR wires are calibrated, the positional uncertainty increases and an approximated correction factor must be applied, resulting in an increased uncertainty. One of the ways to avoid this problem would be to flatten the well chamber response by increasing its sweet spot region. This work uses the Monte Carlo code PENELOPE to simulate the response of a well‐type chamber HDR‐1000, with its original insert, by using an HDR source and proposes a new insert design that increases its flatness region from 1.0 cm to approximately 4.0 cm about the peak response).
Segmental and dynamic intensity‐modulated radiotherapy delivery techniques for micro‐multileaf collimator
Authors: Agazaryan Nzhde , Solberg Timothy D.
Published: July 2003

A leaf sequencing algorithm has been implemented to deliver segmental and dynamic multileaf collimated intensity‐modulated radiotherapy (SMLC–IMRT and DMLC–IMRT, respectively) using a linear accelerator equipped with a micro‐multileaf collimator (mMLC). The implementation extends a previously published algorithm for the SMLC–IMRT to include the dynamic MLC–IMRT method and several dosimetric considerations. The algorithm has been extended to account for the transmitted radiation and minimize the leakage between opposing and neighboring leaves. The underdosage problem associated with the tongue‐and‐groove design of the MLC is significantly reduced by synchronizing the MLC leaf movements. The workings of the leaf sequencing parameters have been investigated and the results of the planar dosimetric investigations show that the sequencing parameters affect the measured dose distributions as intended. Investigations of clinical cases suggest that SMLC and DMLC delivery methods produce comparable results with leaf sequences obtained by root‐mean‐square (RMS) errors specification of 1.5% and lower, approximately corresponding to 20 or more segments. For SMLC–IMRT, there is little to be gained by using an RMS error specification smaller than 2%, approximately corresponding to 15 segments; however, more segments directly translate to longer treatment time and more strain on the MLC. The implemented leaf synchronization method does not increase the required monitor units while it reduces the measured TG underdoses from a maximum of 12% to a maximum of 3% observed with single field measurements of representative clinical cases studied.
Incorporation of a laser range scanner into image‐guided liver surgery: Surface acquisition, registration, and tracking
Authors: Cash David M. , Sinha Tuhin K. , Chapman William C. , Terawaki Hiromi , Dawant Benoit M. , Galloway Robert L. , Miga Michael I.
Published: July 2003

As image guided surgical procedures become increasingly diverse, there will be more scenarios where point‐based fiducials cannot be accurately localized for registration and rigid body assumptions no longer hold. As a result, procedures will rely more frequently on anatomical surfaces for the basis of image alignment and will require intraoperative geometric data to measure and compensate for tissue deformation in the organ. In this paper we outline methods for which a laser range scanner may be used to accomplish these tasks intraoperatively. A laser range scanner based on the optical principle of triangulation acquires a dense set of three‐dimensional point data in a very rapid, noncontact fashion. Phantom studies were performed to test the ability to link range scan data with traditional modes of image‐guided surgery data through localization, registration, and tracking in physical space. The experiments demonstrate that the scanner is capable of localizing point‐based fiducials to within 0.2 mm and capable of achieving point and surface based registrations with target registration error of less than 2.0 mm. Tracking points in physical space with the range scanning system yields an error ofSurface deformation studies were performed with the range scanner in order to determine if this device was capable of acquiring enough information for compensation algorithms. In the surface deformation studies, the range scanner was able to detect changes in surface shape due to deformation comparable to those detected by tomographic image studies. Use of the range scanner has been approved for clinical trials, and an initial intraoperative range scan experiment is presented. In all of these studies, the primary source of error in range scan data is deterministically related to the position and orientation of the surface within the scanner's field of view. However, this systematic error can be corrected, allowing the range scanner to provide a rapid, robust method of acquiring anatomical surfaces intraoperatively.
Measurement of focal spot size with slit camera using computed radiography and flat‐panel based digital detectors
Authors: Rong Xiujiang J. , Krugh Kerry T. , Shepard S. Jeff , Geiser William R.
Published: July 2003

The purpose of this study was to evaluate the use of digital x‐ray imaging detectors for the measurement of diagnostic x‐ray tube focal spot size using a slit camera. Slit camera images of two focal spots for a radiographic x‐ray tube were acquired with direct‐exposure film (DF) (as specified by the National Electrical Manufacturers Association [NEMA] Standards Publication No. XR 5, 1992), computed radiography (CR) imaging plates, and an a‐Si:H/CsI:Tl‐based flat‐panel (FP) detector. Images obtained with the CR and the FP were acquired over a broad range of detector entrance exposure levels. The DF slit images were evaluated according to NEMA specifications (visually, using a 7× magnifying glass with reticule) by six medical physicists. Additionally, the DF images were digitized and the focal spot sizes obtained from the digital profiles of the slit. The CR and the FP images were analyzed in a manner similar to the digitized DF images. It took less than 20 minutes for a complete CR or FP measurement of focal spot size in two dimensions. In comparison, a typical DF measurement with visual evaluation takes at least 60 minutes, in our experience. In addition to a great reduction in measurement time achieved by using digital detectors, the tube loading requirements were reduced to ∼20 mAs compared with ∼1000 mAs when using the DF technique. The calculated focal spot sizes for CR and FP differed from those of digitized DF by −2.4% to +4.8% (σ=2.5%), far less than the −16.6% to +9.3% (σ=8.1%) variability introduced by the visual evaluation of the slit image. In addition, the calculated focal spot sizes for the CR and the FP images maintained a coefficient of variation <1.0% over the broad range of exposure levels. Based upon these results, we conclude that (1) FP and CR detectors yield consistent results in measurements of x‐ray tube focal spot sizes, (2) compared to DF, CR and FP significantly reduce measurement time and tube loading requirements, (3) CR and FP readily permit digital profile analysis, thereby eliminating observer error, and (4) unlike DF, CR and FP are independent of exposure level.
Reference dosimetry at the neutron capture therapy facility at Studsvik
Authors: Munck af Rosenschöld P. M. , Giusti V. , Ceberg C. P. , Capala J. , Sköld K. , Persson B. R. R.
Published: July 2003

The purpose of this publication was to present and evaluate the methods for reference dosimetry in the epithermal neutron beam at the neutron capture therapy facility at Studsvik. Measurements were performed in a PMMA phantom and in air using ionization chambers and activation probes in order to calibrate the epithermal neutron beam. Appropriate beam‐dependant calibration factors were determined using Monte Carlo methods for the detectors used in the present publication. Using the presented methodology, the photon, neutron and total absorbed dose to PMMA was determined with an estimated uncertainty of ±5.0%, ±25%, and ±5.5% (2 SD), respectively. The uncertainty of the determination of the photon absorbed dose was comparable to the case in conventional radiotherapy, while the uncertainty of the neutron absorbed dose is much higher using the present methods. The thermal neutron group fluence, i.e., the neutron fluence in the energy interval 0–0.414 eV, was determined with an estimated uncertainty of ±2.8% (2 SD), which is acceptable for dosimetry in epithermal neutron beams.