bluuebunny/crossref_metadata_2025_split huggingface dataset:
TU‐C‐ValA‐04: Deformable Registration Using Regularization That Accommodates Local Tissue Rigidity
Authors: Ruan D , Fessler J , Roberson M , Balter J , Kessler M 
Published: July 2006

Purpose: Existing methods for deformable image registration typically use homogeneous regularization to encourage global smoothness. Less work has been done to incorporate voxel‐level tissue‐specific elasticity information. Ignoring differences in elasticity can, however, result in non‐physiological registrations, such as bone warping. We propose an approach to incorporate tissue rigidity information using a spatial variant regularization. Method and Materials: Regularized image registration algorithms estimate the deformation by minimizing a cost function, consisting of a dis‐similarity metric and regularization. To account for tissue‐type‐dependent rigidity information, we incorporate into the cost function a non‐rigidity penalty: an integral of stiffness index for local deformation weighted by spatial variant regularization factor depending on tissue type. For CT data, a simple monotonic increasing function of the CT number is used as a rigidity index for local tissue type. A necessary and sufficient condition for stiff local deformation is derived, and the local non‐stiffness is measured by the deviation of local Jacobian from orthnormality using the Frobenius norm. Tensor B‐Splines are used to parameterize the deformation field. A multi‐resolution scheme and gradient‐based approach are applied for optimization. Performance was accessed by registering 3D thorax CT‐images obtained from different breathing phases. Results: Experiments with clinical data demonstrate higher accuracy for inhale‐exhale thorax CT registration with the proposed approach. We observe comparable intensity match as the unregularized approaches, but more physiologically reasonable results with respect to different tissue types; in particular bone warping phenomena is eliminated in general. Conclusion: This work provides a way to incorporate tissue‐type‐dependent information into deformable registration framework with regularization design. Inference from image intensity avoids explicit segmentation, and is robust to partial volume effect. Our formulation based on local Jacobian and Frobenius norm provides analytical expression for the regularization and its derivative. More physiological results are achieved with minor computation expense.Supported by NIH P01‐CA59827.
TU‐C‐230A‐02: Error Analysis/reduction Philosophy/theory
Authors: Pawlicki T 
Published: July 2006

The purpose of this presentation is to discuss the philosophy and theory of error analysis and reduction. This talk will be equal parts conveyance of technical information and provocation to action on the important issue of medical errors. Although a somewhat obvious connection, we begin by providing a sound framework that relates errors and quality assurance. The scope of technical information within this presentation will be an attempt to wade through the myriad of theories and philosophy related to errors and quality, much of which is new to our field. For example, the JCAHO Lexicon describes quality as, “Designing a product or service as well as controlling its production so well that quality is inevitable.” What does it actually mean to control a product or service? This will be described. The leadership of the AAPM has taken the ambitious step to change the emphasis of quality assurance from simply checking specifications to investigating processes via the new quality assurance task group (TG100). This is a significant and necessary paradigm shift in our approach to medical errors and quality that deserves a detailed discussion. An understanding of how to reduce errors and improve quality begins with an appreciation of two realities: 1) everything we do involves a process, and 2) every process has unavoidable variation. If one controls variation in a process, then one will reduce errors and improve quality. The implementation of process identification and control to clinical practice will be discussed in detail and by example where appropriate. Furthermore, there is a significant history of error reduction and quality research and this context will be maintained throughout the presentation. In addition to specific techniques of error analysis and reduction such as failure modes and effects analysis (FMEA), root cause analysis (RCA), pareto charts, fishbone diagrams and statistical process control (SPC) we will discuss the philosophies of define, measure, analyze, improve, control (DMAIC) and total quality management by the six‐sigma approach.Error analysis and reduction (and quality assurance in general) are built on a mature body of research from other fields. There is much work to do toward implementing these techniques in radiotherapy practices to minimize errors and optimize quality. There are no turn‐key solutions to quality. As will be described, the business world has become fanatical about quality to stay competitive. Why should the medical world be any different with our patients' well‐being at stake? Medical physicists, above anyone else in the typical department, have the analytical ability to understand and implement these techniques. We must accept the challenge and as a first step, future AAPM meetings should have a research session specific for quality, error analysis/reduction and cost analysis/reduction.
WE‐C‐330A‐07: Radiofrequency Ablation Electrode Displacement Elastography
Authors: Bharat S , Zagzebski J , Madsen E , Varghese T 
Published: July 2006

Purpose: Elastography can be used to image the position and location of thermal lesions created using radiofrequency (RF) ablation. A challenge, however, when applying this technique to guide treatment of liver tumors is that of producing a controlled compression of the tissue. We are testing a new method, ‘electrode displacement elastography’, for producing elasticity images of ablation therapy treatments. This paper presents results of tests in a custom elastography phantom. Method and Materials: An elastography phantom containing a stiff inclusion (50 kPa) embedded in a soft (11kPa) background was used. A discarded RF electrode was mounted firmly into the inclusion with the handle extending outside the phantom container. A stepper motor applied small (0.1mm) displacements while the phantom was imaged using an ultrasound machine equipped with a research interface, acquiring raw echo data before and after small perturbations of the electrode. One‐dimensional cross correlation was used to estimate displacements. Finite element analyses were also performed to characterize the contrast‐transfer efficiency (CTE) of the conversion from the underlying modulus domain to the observed strain domain. Results: On elastograms the inclusion has a characteristic halo appearance, similar to that observed in in‐vivo tests of this technique. Strain contrast is consistently higher than the underlying modulus contrast, confirmed by a study of the CTE. On simulated strain images, stiffer inclusions in softer backgrounds have CTE values in excess of 0 dB. Conclusions: Feasibility of electrode displacement elastography is shown. The strain contrast observed exceeds the underlying modulus contrast, for stiffer inclusions. This characteristic of the method may provide RF ablation practitioners with added lesion contrast in situations where the actual stiffness ratio between the lesion and surrounding normal tissue is not significantly greater than 1:1.This work is supported by Whitaker Foundation grant RG‐02‐0457.
WE‐C‐330A‐09: Dynamic, MultiModality Imaging: Temporal Precision and US Artifact Reduction
Authors: Oldham S , Molloy J 
Published: July 2006

Purpose: Herein we describe the development of a dynamic fusion technology for ultrasound (US) and other static 3D data sets. We tested whether the high US frame rate is sufficient to accurately track objects subject to respiratory motion. In addition, we used the spatial registration functions of the system to test whether aggressive compounding of US images would be efficacious in terms of artifact reduction and boundary detection. Materials/Methods: The system's dynamic spatial accuracy was tested using a phantom translated at a velocity of either 4 or 16 mm/s. To test inaccuracies due to video processing we offset the arm and video frame data in single frame increments. Static 3D US data sets were acquired incorporating an acoustic obstruction. Data sets were reconstructed using images from multiple angles of interrogation. Similar experiments were performed to assess the system's ability to reduce reverberation artifacts and tested on a human subject. Results: By correcting for video processing latency, the system was able to track object motion to 0.2 and 0.5 mm for speeds of 4 and 16 mm/s, respectively. Aggressive image compounding was able to reveal objects that were otherwise obstructed from a single view. Reverberation artifacts were reduced, in addition to enhancing certain object boundaries . These results were present although less obvious in early human testing. Conclusions: Our imaging system is spatially accurate over a range that permits interrogation of an adult abdomen from a wide range of angles. The system's ability to track respiratory motion has been demonstrated. Aggressive compounding demonstrated that obstructed test objects could be visualized by non‐intelligently summing images from varying angles. Soft tissue boundaries and other US artifacts may also benefit from application of the technology.Supported by NIH R01EB002899.
WE‐C‐330D‐01: The Future of Image Science
Authors: Cunningham I 
Published: July 2006

The characterization and classification of image quality in radiographic imaging is a complex and illusive goal. It involves understanding the physics of x‐ray interactions and how these influence statistical properties of image signals and noise. It requires an understanding of how observers can extract non‐random structures from random (and sometimes not random) image details. Finally, it requires an understanding of how observers are able to extract clinically meaningful information from the complicated clutter of background structural information. As processes responsible for producing image signals are often non‐linear, non‐stationary, multi‐dimensional and task dependent, simpler metrics of image quality and detector performance are at best idealized approximations.Scientists have attacked this multi‐faceted problem from a number of directions. As a result, a wide spectrum of terminology and concepts have become commonplace. This talk will address some aspects of how far “image science” has come and where it may be going. It will highlight accomplishments that have become established in both academic and commercial fields, and problems that have not been solved. Hopefully, improved understanding of these issues will enable the development of better detectors and systems and improved patient outcomes.Educational Objectives:1. Understand issues that influence image quality and observer performance for simple tasks.2. Understand limitations of simple metrics.3. Understand some directions being followed to better understand what determines image quality for the development of better detectors and systems.
WE‐C‐ValA‐04: Derivation of the Tumor Position From External Respiratory Surrogates with Periodical Updating of External/internal Correlation
Authors: Kanoulas E , Aslam J , Sharp G , Berbeco R , Nishioka S , Shirato H , Jiang S 
Published: July 2006

Purpose: To develop techniques that can derive the tumor position from external respiratory surrogates through periodically updated internal/external correlation. Method and Materials: A simple linear function is used to express the correlation between tumor and surrogate motion. The function parameters are established during patient setup session with both tumor and surrogate positions measured at 30Hz rate. During treatment, the surrogate position, constantly acquired at 30Hz, is used to derive the tumor position. Occasionally, a tumor image is acquired to enable the updating of the correlation function. Four update methods are investigated. (a) Line shift. (b) Fit model — through point. (c) Fit model — extra weight. (d) Function difference — fit point. Results: Tumor and external surrogate motion demonstrates a high degree of correlation however it dynamically changes over time. Occasionally updating the correlation function leads to more accurate predictions than using external surrogates alone. At the lowest tumor imaging rate tested in this work (0.1Hz) an accuracy improvement of 10% over the prediction by the mere use of external surrogate was observed for the best update method. Update methods (a) and (b) derive the tumor position with larger accuracy than (c) and (d) in case of high imaging rates. The opposite is observed in case of low imaging rates. Conclusion: Occasional calibration of the tumor/external surrogate correlation during treatment substantially increases the accuracy of the tumor localization compared to tumor position derivation by using the external surrogate alone.This work is partially supported by CenSSIS.
WE‐C‐224C‐03: Analysis of Technical Failures in 1000 Clinical Applications of Pulsed Dose Rate Brachytherapy
Authors: Koedooder C , van Herten Y , van der Grient H , van Wieringen N , van de Kamer J 
Published: July 2006

Purpose: Investigation of safety and reliability of Pulsed Dose Rate brachytherapy within and outside office hours.Method and Materials: More than 1000 patients were treated with two first generation (1996–2004) and three second generation (starting 2004) PDR afterloaders (Nucletron, The Netherlands). The most frequently treated tumorsites were breast, esophagus, gynecology, prostate and bladder. The number of pulses and the overall treatment time ranged from 4 pulses in 30 minutes for esophagus to 62 pulses in 135 hours for anal carcinoma. Apart from treatment‐related parameters the type and frequency of technical failures, e.g. source obstruction, were registered for each treatment. From these data the fractions of disturbed pulses and treatments were determined for all tumor sites. Also the behavior of these fractions over time was studied. Results: Error frequency depended strongly on treated tumor site. For breast 149 out of 5936 pulses were disturbed (2.5%). For prostate the error fraction decreased from 16% in 11 patients to 11.7% after 49 patients. Gynecology scored well with only 28 disturbed pulses out of 2002 pulses given (1.4%).For breast the first error most often occurred in the first pulse. For prostate and bladder the first error occurred in a further stadium of treatment. By applying dummy checkwire runs, errors with the active source occurred only rarely. Our experience is that 98% of the patients received the intended dose correctly. Only in 2% of the treatments an adjustment of implant geometry or planned dose or a cancellation of part of the treatment was necessary. Of these 2% however, about half was caused by medical rather than technical reasons. No significant difference was seen between the first and second generation afterloader type. Conclusion: Errors do occur and are tumor site dependent. Our experience however shows that PDR can be safely applied, also outside office hours.
WE‐C‐224C‐09: Calculation of the Dose Distribution Around a High Dose‐Rate 192Ir Brachytherapy Source Via a Multi‐Group Discrete Ordinates Method
Authors: Gifford K , Price M , Failla G , Wareing T , Horton J , Mourtada F 
Published: July 2006

Purpose: To calculate the dose distribution around a high dose‐rate (HDR) 192Ir brachytherapy source in water by a multi‐group discrete ordinates code and compare with a benchmarked Monte Carlo calculated dose distribution. Methods and Materials: The multi‐group discrete ordinates code, Attila™ version 5.0.2 (Transpire Inc., Gig Harbor, WA) was used to calculate the dose distribution around the Nucletron microSelectron HDR source (Nucletron B.V., Veenendaal, The Netherlands). MCNPX 2.4.k was used to benchmark the deterministic calculations. The source was constructed with Solidworks (Solidworks Corp., Concord, MA), a mechanical design software. The constructed geometry of the source, dose scoring plane and sphere were exported in Parasolid® file format so that it could be imported into Attila.MCNPX 2.4.k was used to compute the Monte Carlo dose distribution. 50 million histories were simulated resulting in standard errors of the mean of less than 5% at a point 7 cm from the center of the source. The source geometry was identical to that of the Attila run except for minor differences in modeling the source due to limitations of the MCNPX code.Dose rate matrices were exported from both codes and imported into an in‐house data analysis software. This software overlaid the matrices and quantified the percent dose difference and distance‐to‐agreement for all points in the matrices. The number of points passing a 2%/2mm criterion were reported. Results: Attila calculated dose to within ±2% or 2mm for 99% of the points. The Attila calculations required approximately 38 minutes of CPU versus 568 minutes for MCNPX on the same CPU. Conclusions: The Attila multi‐group discrete ordinates code accurately calculated the anisotropy from the microselectron HDR source. Attila accurately calculated dose in an efficient manner.
WE‐D‐330A‐01: 3D Optical Imaging of Tumor Microvasculature and Viable Cell Distribution
Authors: Sakhalkar H , Wang Y , Oliver T , Dewhirst M , Oldham M 
Published: July 2006

Purpose: The ability to image 3D global structure (e.g. microvasculature) and function (e.g. gene expression) in whole unsectioned tumors, in high‐resolution and with high‐contrast, is of significant present interest in cancer research. We have developed novel optical imaging techniques capable of reconstructing the 3D distribution of absorbance or fluorescence‐emitting sources in tumor tissue. Primary advantages include high spatial resolution and contrast, and ability to image a wide range of molecular probes.Method and Materials: Constitutive RFP expressing HCT116 (human colon carcinoma) xenograft tumors were implanted in hind legs of nude BALBC mice. The tumor microvasculature was dual‐stained by in vivo tail vein injections of light attenuating isotonic ink and FITC lectin. The tumor was excised post‐staining and subjected to a fluorescence‐friendly clearing procedure to render it amenable for optical imaging. Quantitative images of microvascular density and viable‐cell distribution were reconstructed using tomographic algorithms from a set of transmission and fluorescent projection images acquired at multiple angles using appropriate filters, focusing optics and a CCD camera.Results: Co‐registered, multimodal, high‐resolution and high‐contrast 3D reconstructions were achieved through large, (∼1cm) whole mount, murine tumor samples. Quality assurance tests indicated encouraging accuracy of reconstructed attenuation coefficients and geometry. The 3D reconstructed slices were juxtaposed with histological slices of the same tumor to reveal striking correlation between viable‐cell distribution and well‐perfused regions. A fluorescence friendly clearing procedure was identified.Conclusion: We present a novel technique for multi‐modality optical imaging of 3D microvasculature and/or viable cell distribution in tumor tissue with unprecedented image resolution and contrast. The technique has potential to image a wide variety of tumor and normal tissue structure and function. Of particular interest is the potential to analyze the effect of anti‐angiogenic agents and radiation therapy on the response of the entire 3D tumor microvasculature network.
Po‐Thur Eve General‐11: Data for Intensity Modulated Radiotherapy Planning with Pinnacle for a 6MV Siemens Primus Beam
Authors: Ozard S 
Published: July 2006

Background and purpose: Intensity‐modulated radiation therapy (IMRT) with a Siemens Primus linear accelerator and the Pinnacle V7.6c (IMRT V2.0) treatment planning system requires additional measurements and quality assurance (QA). This study presents the small field data for a 6MV beam and results of the additional QA for small monitor unit (MU) fields and the multi‐leaf collimator (MLC).Materials and methods: Beam measurements included relative output factors, MLC transmission and MLC interleaf transmission, percentage depth doses, and dose profiles. Beam modeling in Pinnacle is discussed. QA measurements included MU linearity and stability, MLC leaf position and abutment, and small MU field symmetry and flatness.Results and discussion: For field sizes 2×2cm2 and larger, ROFs for the two linacs were well within 0.6% of one another. MLC transmission and MLC interleaf transmission agreed with published values. The penumbral width was larger for the upper Y jaws compared to the lower MLC collimator by 1.4mm for the 2×2cm2 field. The Pinnacle model parameters that were adjusted to improve the fit to measured data were C2, K and ECD10×10, as well as the source size. MU linearity was adjusted to reduce the linearity error introduced for small MU IMRT segments. MLC leaf abutment test results are consistent with results at other centres with the same MLC.Conclusions: MU stability and MLC leaf position calibration have an important influence over the accuracy of the delivered dose for small MU segments. Field flatness in the inplane direction will also degrade dose accuracy for small MU segments.
Po‐Thur Eve General‐35: Official statistics generated using a commercial R&V system in the Canadian context
Authors: Gelinas D , Tanguay M 
Published: July 2006

In Quebec every radiotherapy department has to present official statistics to the government known has technical units. All actions taken by therapists generate technical units roughly related to the amount of time needed to complete the task. Technical units are defined per category and task by the officials.A commercial record and verify system, VARiS version 7.2 from Varian Medical Systems, has successfully been configured to automatically capture the required technical units in Quebec. VARiS is normally installed preconfigured to collect charges in the United States using Medicare codes and charges through the application Activity Capture. This program interacts with other applications of the R&V system to greatly ease the process of confirming chargeable activities as they are completed. Replacing the Medicare codes with the Quebec codes in the administration module was the most demanding task.At treatment machines, a window will automatically appear when a treatment session is completed to confirm the activity to be charged. The application will suggest the same codes that were completed the last time. In the case portal images were acquired, the configured code will be suggested even though the code was not used in the prior session.Technical units generated elsewhere, for example in dosimetry, are computed using a single predefined template attached to every patient. The therapist searches the template for the proper code and manually completes it so that it is taken in to account in the patient's statistics.