bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐SAMS‐L100J‐01: Determination of Dose From CT Examinations
Authors: Boone J
Published: July 2007

The assessment of radiation dose from computed tomography has become an important issue due to the increased utilization of computed tomography in a large number of clinical applications, from CT urography to cardiac CT. The traditional metrics used for CT dose assessment (CTDI‐100) have come under assault from a number of investigators, because of its limitations in describing the radiation dose in realistic CT examinations. While there remains no real consensus in the field, a number of groups are working on the development of CT dose metrics which convey a better understanding of the radiation dose received by individual patients for specific CT examinations. In this presentation, the perspective of a number of groups will be presented. Primarily, the work of a committee of the International Commission of Radiological Units (ICRU) commissioned in 2005 will be discussed.

The ICRU committee has preliminarily defined a multi‐tier system for the assessment of radiation dose metrics in computed tomography. At the first level, machine‐dependent performance factors are described and measured, and these include the traditional CTDI‐100 metric for the 16 cm and 32 cm diameter polymethylmethacrylate dosimetry phantoms, at the center and at the periphery. There is a consensus amongst the ICRU community that radiation dose to patients undergoing CT examinations is best established using the known geometry of the CT examination, coupled with measured output characteristics of the specific CT scanner (including bow‐tie characteristics), combined with Monte Carlo computations. In the rare instance in which the CT dose to a specific patient needs to be computed, image‐based methodologies will be presented which enable these computations with a high degree of accuracy. It is emphasized that the effective dose (measured in milliseiverts) is not an appropriate measure for individual patient doses, as this metric includes population‐based radiation epidemiological data which may not be applicable to a specific individual. Therefore, the ICRU efforts towards radiation dosimetry of the individual patient focus on dosimetric units which are physical in nature, and describe the individual organ doses and the overall average dose to the patient, depending upon the specific CT examination and the patient's physical characteristics.

Educational Objectives:

1. Convey some of the issues in accurate dose assessment in CT.

2. Describe some of the ongoing efforts of the ICRU committee on CT towards dose assessment.
TU‐C‐L100J‐01: Commissioning of New Modalities for PACS
Authors: Walz‐Flannigan A , Langer S , Fetterly K
Published: July 2007

Purpose: Though equipment and software may claim to be DICOM compliant, interaction with a given electronic environment may result in unexpected problems from poor image quality to a disabled PACS. In order to prevent clinical disruption as a result of introducing a new modality into our electronic environment, we sought to institute a commissioning process that ensures rigor in testing and provides a record of outstanding issues. Methods: We developed a generic testing protocol which encompasses connectivity, workflow verification and image quality. The protocol is designed to be adaptable to the requirements of different modalities. First, analysis is done with images created in and sent through a “test” electronic environment which replicates the system used in production (RIS, PACS, worklist broker, clinical viewer and archive). Once the images have passed the “test” system, and we are confident that the modality will not disrupt clinical workflow, the same testing procedure is continued in the “production” system. In our case, testing is a coordinated effort amongst four groups (IT, Engineering, Radiology Systems Coordinators, and Medical Imaging Technology Specialists). A web based tool was set‐up to facilitate document sharing, multiple‐author‐editing of data collection forms and communication between groups. The testing protocol itself consists of five main categories each of which are detailed by each group according to their roles. Results: The testing protocol was used in the installation of a digital radiographic unit that was never before seen by our PACS. With this, problems were found and modifications to the modality and PACS were made. Conclusion: With the complex interdependent software systems involved in the practice of radiology, adding new systems to a network often results in unintended dire consequences. To mitigate clinical disruption, we've established a commissioning procedure that will be required for introducing new equipment or software into our electronic environment.
TU‐C‐M100F‐01: Development of a Linac‐MRI System for Real‐Time ART
Authors: Fallone B , Carlone M , Murray B , Rathee S , Stanescu T , Steciw S , Wachowicz K , Kirkby C
Published: July 2007

Purpose: To describe the novel design of the coupling an of MRI to a medical linac to provide real‐time tracking of the tumor and healthy tissues during irradiation by the treatment beam Method and Materials: Various embodiments are defined in our patents (Fallone, Carlone, Murray) to avoid mutual interference between the MR and the linac. Our method allows rotation of a linac with respect to the subject to allow irradiation of the subject from any angle without disturbing the magnet homogeneity. Magnetic shielding of the linac prevents disturbance from the MRI. RF signal shielding, modifications the RF‐signal triggering and pulse shaping are used to minimize linac interference of MRI RF read sequences. Various Monte Carlo calculations (EGS4 NRC and Penelope) and finite‐element analyses (Comsol) are performed in all design stages. Results: The initial design for the human system involves a bi‐planar MRI with 65 cm opening to allow rotation of the shoulders within the bore. A short 6 MV waveguide is coupled to one open end of the MR, and a beam‐stop and a projection imaging device (eg, flatpanel) is coupled to the other end. Rotation is provide by two concentric rings, and the permanent‐magnet design is preferred in the initial stage to provide stability and lack of electric wiring in the rotation process. Low fields allows very small fringe fields to minimize linac interference yet with adequate image quality of soft tissue for lungs, prostate, GBM, etc. Mutual interference issues and other issues arising externally are calculated and resolved. Conclusion: We have shown the design to be a practical, viable and realizable within a reasonable time frame. Our other presentations detail resolutions to mutual MRI‐linac interferences.
TU‐C‐M100F‐03: MRI‐Controlled Transurethral Ultrasound Therapy for Prostate Cancer
Authors: Bronskill M , Chopra R
Published: July 2007

Purpose: To develop and test a transurethral ultrasound therapy system which uses quantitative real‐time MRI temperature feedback to control the shape of the coagulated region within the prostate while sparing surrounding structures from thermal damage. Method and Materials: An MRI‐compatible transurethral heating applicator comprised of planar ultrasound transducers that produce a directional heating pattern has been constructed. This device is rotated within a 1.5T MR imager to distribute energy to targeted regions of the prostate by an MRI‐compatible motor, concurrent with imaging. The region of the prostate to be treated is selected based on MR imaging information. Subsequent heating is controlled by MRI temperature images acquired every 5s and a complete prostate volume can be coagulated with a single rotation in about 20m. In‐vivo experiments have been performed in a canine model and the spatial accuracy of the coagulation patterns has been assessed using contrast‐enhanced MR images and a novel, quantitative whole‐mount histology technique with image registration to the MR temperature maps. Results: Sufficient spatial resolution and temperature accuracy can be obtained at 1.5T to provide accurate feedback control of the coagulation pattern within ±1.5mm of the targeted heating radius. Histological analysis indicates that, under these treatment conditions, the margin between completely coagulated tissue and apparently undamaged tissue is ⩽3mm in this acute assay. These histological boundaries, when registered carefully with the quantitative MRI temperature histories, provide a good estimate of the temperature threshold (54.6±1.7°C) for complete coagulation. The contrast‐enhanced MR images clearly show the coagulated region but register less accurately with the histological boundaries. Conclusion: Successful control of transurethral ultrasound therapy using quantitative, real‐time MRI temperature images has been demonstrated in vivo. This technology offers good potential for an effective treatment for localized prostate cancer with reduction in morbidity.
TU‐C‐M100F‐05: Automated Classification of Substructures of White Matter Via Anisotropic Water Diffusion
Authors: Cao Y
Published: July 2007

Purpose: Diffusion tenor imaging (DTI) has been shown to be a valuable technology for in vivo assessment of white matter (WM) diseases, and has potential for monitoring the effect of radiation on WM structures. The aim of this work is to develop an automated method for classification of substructures of normal‐appearing and disease‐affected white matter (NA and DAWM) from diffusion tenor images. Methods: The methodology is based upon the fuzzy c‐means clustering algorithm with nearest‐neighbor spatial constraint to enhance spatial continuity and overcome intensity inhomogeneity. To resolve substructures of WM and grey matter (GM), which are obscured by large diffusion coefficients and variations in cerebral‐spinal fluid (CSF), a two‐layer hierarchical tree of fuzzy classification was developed. In the first level of classification, tissue is segmented from CSF or a fluid‐like class. Then, tissue is further partitioned into subclasses based upon their characteristic anisotropic water diffusion. We tested which feature space could result in better classification, in which the DTI data were presented as diffusion‐weighted data, elements of the diffusion tenor, and eigen‐diffusivities. We applied the method to DTI data from patients with normal‐appearing WM, low grade glioma, meningioma, and benign brain tumors. Resolved structures of NAWM and GM were compared to a brain atlas. Results: Eigen‐diffusivities resulted in most robust classification of substructures than other forms of data. Resolved substructures included genu and splenium of corpus callosum, corticospinalfibers, subinsular WM, optical radiation WM, internal capsule, caudate nucleus, lenticular nucleus, and thalamus. Necrotic tumor and edema regions of WM were identified with either a fluid‐like or sub‐tissue class, depending upon the water content, and viable tissue. Conclusion: We have developed a robust method for classification of substructures of NA and DA WM and GM using DTI. The differentiated substructures could be useful for radiation treatment planning, and for monitoring radiation effect.
TU‐C‐AUD‐08: A Web‐Based and Database‐Centric Radiotherapy Treatment Plan Review and Reporting System
Authors: Khullar D , Mullen D , Deasy J
Published: July 2007

Purpose: The typical current treatment plan approval process is to assemble the planner and the reviewing physician at the planning workstation and review the plan using the planning software system. We are developing a new web‐based and database‐centric tool to address these problems, called WEBTREV (Web‐based TReatment EValuation). Method: WEBTREV utilizes several development tools, including the object oriented web development platform Ruby‐on‐Rails (ROR), the open‐source database MySQL, and CERR, the Matlab‐based open‐source treatment planning research system. CERR is used to extract DICOM‐RT data from planning systems and to generate customized views and reports. The corresponding extracted plan images and plan evaluation parameters are stored in the MySQL database. Ruby‐on‐Rails dynamically defines views and serves data over web pages via the Apache web‐server system.

Results: The resulting workflow is: A dosimetrist uses a secure login via ROR at the planning system to push DICOM to a receiver where CERR is used to generate static images of overlaid scans, doses, and structures. As soon as this process is complete, ROR sends an e‐mail to the dosimetrist to confirm the upload. Once confirmed, a physician can log into a personal database work queue and select the patient to review. The dynamic webpage contains standard views of slices and structures, as well as dose‐volume‐histogram data and customized reports giving plan metric values (e.g., D95 and minimum dose to target volumes). Approval or a request for further modifications is transmitted back to the dosimetrist, who may view comments linked to graphics. Conclusions: WEBTREV provides a promising platform for reviewing treatment planning data remotely. This framework provides a tool for generating consistent representations and reports of dose characteristics, images, and structure data, as well as plan evaluation parameters, across different planning systems.
TU‐C‐AUD‐09: Comprehensive Assessment Methodology for Radiation Oncology Information Systems
Authors: Fong L , Herman M
Published: July 2007

Purpose: To develop a comprehensive methodology to systematically assess the information flow and the performance of radiation oncology information systems (ROIS). Method and Materials: Radiation oncology information objects were classified into Clinical Processes, Information Management and Technological Innovation Integration. Comprehensive maps of the IS/IT infrastructure, processes and information flow were generated by a team of experts. These maps served as the basis for testing and evaluating connectivity and process flow and to guide the development of a quantitative survey to assess the performance of an ROIS. Performance was defined as a measure of how the ROIS matches the site‐specific clinical practice and IS/IT infrastructure. Each group of tasks, activities and processes, associated with the three areas classified above, were hierarchically controlled according to importance in patient care and scored by the team members. The survey was applied and experiential feedback recorded in a sample of clinical areas for two test ROIS. Results: Practice specific process and infrastructure maps were generated. Functional and interoperability problems were identified and some resolved during the mapping process. The developed survey was applied and initial results indicate a range of ROIS compatibility with clinical process. While different, each ROIS demonstrated above adequate performance. Experiential feedback provided suggestions to improve ROIS integration and site‐specific processes. Conclusion: This work attempts to provide an objective tool to understand and analyze information flow and its compatibility with a given ROIS in a clinic specific patient care setting. Mapping provides insight into process communication, interoperability and efficiency. The hierarchy and importance of various characteristics are customizable to a given clinical practice and thus allow the tool's broad applicability. Proper assessment of information flow and matching to an ROIS will provide a more efficient and more effective care delivery setting. Conflict of Interest: Supported in part by Varian Medical Systems.
TU‐D‐L100J‐03: Initial Phantom Evaluation of a Surface Imaging System (GateCT®) for 4‐D CT
Authors: Zhao H , Hubenschmidt J , Malinowski K , Parikh P
Published: July 2007

Purpose: Many external surrogates exist for 4‐D CT, but all require some device attached to the patient. We evaluated a markerless optical surface imaging system for use with 4‐D CT. Method and Materials: A prototype of the GateCT optical surface imaging system (VisionRT, London, UK) was installed with a Philips Brilliance 64 CT simulator (Philips Medical, Cleveland, OH). The system is similar to the AlignRT product, but only contains one camera pod which is focused on the bore of the CT scanner. It also monitors the x‐ray on signal and sends regular pulses to the scanner similar to other external respiratory surrogates. First, a static plate was imaged to detect any drift in the measured motion. Next, the 4D phantom was used to create sinusoidal motion with simultaneous longitudinal motion to model breathing whilst the patient was scanned, and the motion measured by GateCT was compared with the phantom motion. Next, the 4‐D phantom moved a 2 cm marble in a sinusoidal pattern, and the scanner was operated in retrospective helical mode. The respiratory waveform was exported from the GateCT program to the scanner, and the inspiration and exhalation image sets were reconstructed and compared. Results: When the phantom was still, the GateCT point track gave a stable reading with a noise level of 0.5 mm. When the phantom was moving in one or two dimensions, the GateCT point track accurately recorded the amplitude, phase and frequency of the motion. For the 4‐D CT scans, the reconstructed CT images indicated that the amplitude, phase, and frequency of the marble motion were recorded accurately by GateCT. Conclusion: GateCT hold potential as a markerless respiratory surrogate. More work is necessary to determine the optimal patient selection for this technique.
TU‐D‐L100J‐06: Detector Technologies for Photon Counting/energy Resolving X‐Ray and CT Imaging
Authors: Shikhaliev PM
Published: July 2007

Purpose: To evaluate existing and a new detector technologies for photon counting/energy resolving x‐ray and CT imaging. Materials and Methods: Digital mammography with photon counting Si and gaseous Xe detectors is now available. Although CZT and CdTe detectors are more attractive for photon counting x‐ray and CT imaging, they suffer from hole trapping and charge sharing between pixels, which decrease energy resolution, count rate, and spatial resolution. We have proposed using CZT/CdTe crystals in a tilted angle configuration when the x‐ray hits the crystal surface at a small angle. This allows decreasing crystal thickness significantly while maintaining high photon absorption. The tilted angle CZT/CdTe was simulated for 0.3–1 mm crystal thickness, 10°–90° tilting angles, and 50–150 keV photon energies. The results were compared to a crystal with 3 mm thickness used in normal irradiation. Experiments were performed with a tilted angle CZT with 2 mm crystal thickness using 59 keV and 122 keV photons and 110 kVp x‐ray. Results: The count rate of the tilted angle CZT detector was higher by 10–20 times for 0.3–1 mm crystal thickness and 50–150 keV photon energies compared to CZT with normal irradiation. The electron collection time was shorter by 3–6 times. The charge diffusion and charge sharing between pixels was decreased correspondingly. The experiments have shown significant decrease in tailing of the energy spectrum with tilted angle detector. The peak/tail ratio of the measured energy spectrum was increased by 2.4 and 2 times for 59 keV and 122 keV photons, respectively, when 20° tilting angle was used. Conclusion: The proposed tilted angle CZT/CdTe detector allows significant increase in count rate, energy resolution, and spatial resolution, as compared to currently used CZT/CdTe detectors. This potentially enables using tilted angle CZT/CdTe detectors for photon counting/energy resolving x‐ray and CT imaging.
TU‐D‐L100F‐02: PET Biomarkers in Radiation Oncology
Authors: Pugachev A
Published: July 2007

Recently, the role of PET and PET/CT imaging in oncology has grown dramatically. The following characteristics of PET make it an ideal imaging modality for providing functional information that can be incorporated into radiation treatment planning:

1. Ability to image nanomolar tracer concentrations.

2. Excellent tissue penetration.

3. Ability to use tracers analogous from the chemical point of view to their naturally‐occurring counterparts.

However, while general paradigm of biologically‐conformal radiation therapy has been proposed long time ago, we are still far from its implementation in routine clinical radiation treatment planning. Even in the case of such a well established tracer as 18FDG, we are still not certain of how to incorporate the information content of an FDG PET image into radiation treatment plan. While multiple approaches to FDG PET image segmentation designed to allow for tumor delineation have been proposed, all of them are failing to take into account the following factors:

1. Complexity of the tumor boundary (even assuming that the boundary does exist).

2. Highly heterogeneous morphology of the lesion.

3. Variability of intratumoral FDG uptake even in homogeneous animal tumor models.

We believe that in order to facilitate further incorporation of PET imaging in radiation treatment planning, the following developments have to take place:

1. Implementation of higher standards of tracer validation. It is not sufficient to show that a tracer designed to image a certain function, like cell division, or an environmental parameter, like hypoxia, is characterized by high tumor uptake. Instead, it is necessary to demonstrate and in‐vivo that the tracer is in fact binding to the desired target. This can be done by performing carefully designed validation studies utilizing animal tumor models and patient tumor tissue specimens.

2. Discrete approaches to PET image segmentation (tumor vs. normal tissue, hypoxia vs. normoxia) have to be dropped in favor of probabilistic approaches. For example, gradual change of FDG uptake from low level in normal tissue to high level in the lesion has to be interpreted as a gradual change in probability of finding a tumor cell, rather than used to randomly assign location of a step‐like target boundary.

The overall goal of this presentation is to provide a short overview of the role of PET in radiation therapy treatment planning and to outline some of the research directions that should allow for the development of PET‐based biologically‐conformal radiation therapy.
TU‐D‐L100F‐03: Quantification of PET and SPECT Biomarkers
Authors: Saffer J
Published: July 2007

The metabolic information provided by PET and SPECT has great potential for diagnosing and staging disease, customizing treatment doses for a particular patient, and tracking a patients' response to treatment. However, quantifying the information in these images remains challenging. This presentation will review the sources of variability in the data, grouped into three broad categories: patient — related factors (e.g. body habitus, medications); scanner‐related factors (spatial and energy resolution, sensitivity, data acquisition mode (2D or 3D), attenuation and scatter correction method, image reconstruction algorithm, respiratory and cardiac motion‐correction method); and operator‐related factors such as acquisition and reconstruction protocols, instrument and image quality control, instrument calibrations, and method of image analysis. The impact of these variables on quantification will be discussed, along with methods for minimizing those that are controllable.

The presentation will conclude with a review of current efforts by government agencies, professional organizations, academic institutions, and sponsors of multicenter trials to grapple with the additional complexities that arise from combining data from multiple patients at multiple sites. Particular emphasis will be placed on the author's experience as a member of the PET Quality Assurance Committee at the American College of Radiology Imaging Network (ACRIN) PET Core Lab, which has credentialed more than 100 PET scanners for participation in quantitative PET multicenter trials.

Research partially supported by ACRIN. ACRIN is sponsored by the National Cancer Institute and receives additional support from industry partners, other governmental agencies and the ACRIN Fund for Imaging Innovation.

NOTE: ACRIN is sponsored by the National Cancer Institute and receives additional support from industry partners, other governmental agencies and the ACRIN Fund for Imaging Innovation.

Educational Objectives:

1. Understand the factors that affect the variability and accuracy of PET and SPECT biomarker quantification, with particular emphasis on scanner‐related parameters.

2. Understand the importance of minimizing variability in order to enhance the ability to distinguish signal from noise.

3. Understand the efforts currently underway to standardize acquisition and processing protocols and to monitor equipment performance through credentialing and periodic quality control checks.
TU‐D‐M100F‐01: A Novel Quality Assurance Monitor for Real‐Time Verification of IMRT and IGART
Authors: Islam M , Norrlinger B , Fan C , Smale J , Galbraith D , Heaton R , Jaffray D
Published: July 2007

Purpose: To develop an independent treatment verification method which can validate radiation field delivery in real‐time throughout the treatment course. The system is designed to capture common treatment delivery errors, and is intended to eliminate the need for pre‐treatment dosimetric quality assurance of intensity modulated radiation therapy (IMRT) and enable the implementation of image guided adaptive radiation therapy. Method and Materials: A monitoring system, termed Integral Quality Monitor (IQM), has been developed that utilizes an area integrated energy fluence monitoring sensor (AIMS) positioned after the final beam shaping device (i.e. multileaf collimator (MLC)) and a signal prediction algorithm, IQM_Calc. The AIMS consists of a novel large area ionization chamber with a gradient oriented along the direction of the MLC motion. The measured signal from the AIMS can be compared in real‐time with the IQM_Calc predicted values. A prototype AIMS has been built with 2 mm thick Aluminum plates, an area of 22 cm × 22 cm and continuously varying electrode separation of 2 to 22 mm. The IQM_Calc uses a modified sector integration of MLC defined apertures and accounts for MLC characteristics such as: rounded leaf ends, transmission, and relative output factor. Testing of the IQM system was performed on Varian and Elekta linear accelerators. Results: Initial results for prostate IMRT fields show an average agreement of 2% between the measured IQM signals and the IQM_Calc results. For a 3 mm simulated MLC leaf positioning error, the signal of a prostate IMRT field changed by 2%. Conclusion: It is demonstrated that the prototype IQM system has the capability of verifying the accuracy of treatment delivery in real‐time. The system is also capable of capturing common treatment errors. The IQM system has the potential of playing an important role in the challenging QA environment of modern radiation therapy.
TU‐D‐M100F‐04: Characterisation, Commissioning and Evaluation of DELTA4 IMRT QA System
Authors: Sadagopan R , BenComo J , Martin R , Balter P , Vedam S , Nilsson G
Published: July 2007

Purpose: Characterize, commission and evaluate a dual plane diode matrix IMRT QA device. Method and Materials: A novel device consisting of diode matrices in two orthogonal planes inserted in a cylindrical acrylic phantom of 22cm diameter is characterized, commissioned and evaluated for radiotherapy quality assurance. The system interfaces readily with a networked computer making the whole IMRT QA process very efficient in multi accelerator and multi physicist department. It detects charge per accelerator pulse, computes and displays measured dose distribution in 3D space. The temperature dependence of the diode is corrected. The precision, stability, pulse rate dependence, dose rate dependence, angular dependence, linear response, energy response of the system and the calculation accuracy at non detector locations are evaluated in addition to comparing multiple simple and complex iso‐dose distributions from TPS to measured distributions. The software readily analyses dose profiles in any orientations, %dose, DTA and gamma index of the entire 3D distributions. Results: The precision and the day‐to‐day reproducibility of measured data of a single field are excellent, making additional ion chamber measurement unnecessary. The measured data indicated excellent dose linearity and pulse rate independence. Comparison of simple and complex treatment plans with delivered treatment showed good agreement considering the error bars. Conclusions: The Delta 4 system is highly efficient, accurate and reproducible. The instantaneous and automatic data acquisition combined with the error analysis, report and database capability built into the system make it easy, convenient and efficient to use in a busy clinic. Conflict of Interest Statement: One of the co‐author is President and CEO of ScandiDos AB Company, which supplied Delta4 at no cost for evaluation.
TU‐D‐M100F‐05: Pre‐Treatment Verification of Large‐Field IMRT Dose Painting Plans for Head and Neck Cancer Using a Commercial QA Device
Authors: Song Y , Obcemea C , Muller B , Mychalczak B , Burman C
Published: July 2007

Objective: To develop a practical procedure for routine pre‐treatment verification of large dose painting fields using a commercial IMRT QA device, MapCheck. Materials and Methods: Optimized dose painting intensity maps were applied to a 40×40×40 cm3 digital phantom. With a voxel size of 1 mm3, the dose distributions were re‐calculated for a coronal plane at a depth of 5 cm. The DMLC files were then transferred to a Varian Clinac for plan verification. We first delivered a beam with MapCheck at isocenter. The isocenter was then shifted superiorly and inferiorly by 4 cm, respectively. Two more exposures were made. The isocenter was shifted to the left and right by 4 cm, respectively. Two more exposures were made. To detect accurately the steep dose gradient regions, we doubled the effective detector surface density by shifting the isocenter by 5 mm along the X and Y axes. Two more exposures were made. Finally, we merged all these files to yield a desirable dose distribution. We used three different criteria for data analysis: percent difference, distance to agreement (DTA), and γ index. We set the percent difference threshold to 3% and the DTA to 3 mm. Results: Using these criteria, 99% ∼ 99.5% dose points passed the test for most of our IMRT dose painting plans. For a ten‐field plan, it took about 35 minutes to complete the data acquisition and post‐analysis. Conclusions: The proposed procedure not only improves the efficiency, but also enhances the accuracy of measured dose distribution in the steep dose gradient regions. MapCheck is a handy, fast, and practical tool for routine pretreatment verification of large‐field dose painting plans.
TU‐EE‐A4‐03: A Comparison of Anatomical Noise Properties Between Breast CT and Projection Breast Imaging
Authors: Metheany K , Boone J , Abbey C , Packard N
Published: July 2007

Purpose: To compare the statistical properties of the anatomical noise present in breast images. Images from a dedicated breast CT scanner are compared with mammographic projection images. Method and Materials: A dedicated breast CT (bCT) scanner was used to image the breasts of volunteers and patients. Twenty‐five of the available 105 patient datasets were selected for analysis. Noise power spectra (NPS) calculations were performed on the datasets for the right breast of the 25 patients in order to examine the statistical nature of the anatomical background of the breast. The projection images acquired at 80 kVp during the cone beam breast CT acquisition were analyzed using NPS calculations. Approximately 50 projection images and 50 bCT slice images were analyzed per patient. Three regions of interest (ROIs) were used per image. The ROIs were randomly distributed within the boundary of the breast. The 2D NPS was calculated for each ROI and the average 2D NPS was computed and averaged radially yielding a 1D NPS. A power law expression of the form αf−β was computed from the results of the projection and bCT images, and the β values were compared. Theoretical development suggests that the β for bCT should be one less than that of the projection images, i.e. β [bCT] = β [proj] − 1. Results: The β values for the bCT slice images were consistently less than those for the projection images. The difference ranged from 0.90 to 2.15, with the average difference being 1.34. The β values for projection images were consistent with the 2.8 value described by Burgess (2001). Conclusion: Lower β values from the NPS results of the bCT images could quantitatively indicate potential improvement in detection ability. More work is needed to conclusively say if this is the case.
TU‐EE‐A3‐03: Performing Concurrent Kilovoltage Imaging While Delivering Megavoltage Treatment Beams
Authors: Yin F , Yoo S , Wu Q
Published: July 2007

Purpose: To investigate the clinical feasibility of performing concurrent kilovoltage (kV) x‐ray imaging while the patient at the treatment position was irradiated by megavoltage (MV) beams. Method and Materials: Anatomical visibility and contrast details in kV images acquired with and without concurrent MV irradiations were compared. An on‐board imager (OBI) mounted to the gantry of a Varian 21EX Linac with an electronic portal imager (EPI) was used in this study. A pelvis (Rando) and a contrast (Vegas) phantoms were placed near the treatment isocenter with a detector‐to‐isocenter distance of 50 cm. The effect of MV beam and its dose rate on noise‐to‐signal ratio (NSR), defined as the ratio of the standard deviation to the mean pixel value in a region‐of‐interest (ROI), and relative contrast, defined as the ratio of mean pixel values between the signal ROI and the background ROI, were studied based on Vegas phantom. Results: Scattering MV beams and electronic noises due to kV detector scanning rate and MV beam pulse rate are two major factors affect the concurrent kV image quality. The calculated NSR increases as dose rate increases. Compared to kV images without concurrent MV irradiation, the NSRs of the contrast phantom were increased by a factor of 2.6 with 300MU/min MV beams and 4.5 with 600MU/min MV beams. However, the relative contrasts were increased by a factor of 1.02 with 300MU/min MV beam and 1.06 with 600MU/min MV beam. Conclusion: It is clinically feasible to acquire concurrent kV images during treatment with MV beams. The kV image quality may be improved by minimizing MV scattering effect and by correcting electronic noises. The ability to take kV images with concurrent MV irradiation allows real‐time verification and tracking of moving target during the gated treatment.

Partially supported by a research grant from Varian Medical Systems.
TU‐EE‐A1‐01: Validation of a Prototype Deterministic Solver for Photon Beam Dose Calculations On Acquired CT Data in the Presence of Narrow Beams and Heterogeneities
Authors: Wareing T , Vassiliev O , Failla G , Davis I , McGhee J , Barnett D , Horton J , Mourtada F
Published: July 2007

Purpose: To evaluate a deterministic method for solving the neutral and charged particle transport equations in cases where electron disequilibrium is significant. Methods and Materials: A prototype deterministic solver, Acuros®, has been developed and validated for photon beam radiotherapy. Acuros is based on the Attila® radiation transport code, which solves the differential form of the linear Boltzmann transport equation for neutral particles, and the linear Boltzmann‐Fokker‐Plank transport equation for charged particles. The angular and energy dependent photon and electron flux is solved at every spatial unknown in the computational domain, and quantities such as dose‐to‐medium (DM) are obtained by multiplying the energy dependent particle flux by the energy dependent energy deposition cross section for the associated image pixel material. Comparisons were made with the Monte Carlo code EGSnrc (DOSXYZnrc) for a head‐and‐neck case having eight 1.5×1.5 cm2 photon beams with a 6 MV photon spectrum. The Acuros calculation used 123,000 elements. Since four spatial unknowns were solved in each element, this equated to 492,000 spatial degrees of freedom.The DOSXYZnrc calculation used 2.5×2.5×2.5 mm3 voxels. Results: Results were compared at 95,183 image pixels where dose > 5% of Dmax. 99.02% of pixels satisfied the 3%/3mm criteria (94,251 out of 95,183 pixels). Computational times for the Acuros and DOSXYZnrc calculations were approximately 19.6 CPU minutes (2.2 GHz Opteron processor)and 2,890 CPU minutes (0.4% avg. uncertainty in voxels > Dmax/2), respectively. Through a rewritten, radiotherapy specific solver, Acuros computational times were further reduced to 7.45 CPU minutes without affecting accuracy. When only doses in regions greater than 20% of Dmax are of interest, computational times are further reduced to 3.08 CPU minutes. Conclusions: A clinically viable combination of dose calculation speed and accuracy has been achieved using a radiotherapy specific deterministic solver.

Research funded in part by NIH grant 1R43 CA105806‐01A1.
WE‐E‐BRA‐02: Use of the 4D Phantom to Test Real‐Time Targeted Radiation Therapy Device Accuracy
Authors: Malinowski K , Lechleiter K , Hubenschmidt J , Low D , Parikh P
Published: July 2007

Purpose: To create a motion fixture capable of testing real‐time targeted radiation therapy delivery systems. Method and Materials: The 4D Phantom is a custom positioning system with stages for accurate reproduction of 3D internal tumor motion and 1D external surrogate motion. A standard film box filled with solid water was sent through two 3D lung tissue trajectories, one from 4DCT and spirometry data and the other measured from a fiducial marker that had been bronchoscopically implanted in a canine lung. An external trigger synchronized motion with the beginning of therapy, and the 4D Phantom gated the linear accelerator via a reed relay based on the real‐time longitudinal position of treatment isocenter. The gating windows, 3mm and 4mm long, encompassed end‐expiration for each motion trajectory. A four‐field, 6MV, 3DCRT plan from a randomly chosen lung cancer patient was delivered and measured for static and for gated and ungated treatments with each motion trajectory. The distance from the edge of the film to the edge of the treatment field was used to align pairs of films for analysis in RIT. Results: The dose distributions' relative positions varied within 2–6mm. Post‐alignment comparisons between static and motion films revealed large misdosed regions. The gated films had fewer areas and smaller magnitudes of dosimetric error than did the ungated films, but hot spots of 10% error were present even in the gated films. Conclusion: The experiment revealed a systematic shift in that the dose was centered at an average phantom position rather than the planned treatment isocenter. Additionally, although gating reduces dosimetric errors due to tissue motion, they can occur during gated radiation delivery. Further work is needed to determine if static film dosimetry is sufficient for QA of gated therapy. The 4D Phantom is capable of improved real‐time targeted radiation therapy QA.
TH‐C‐M100E‐09: Assessment of Skin Dose for Breast Chest Wall Radiotherapy as a Function of Bolus Material
Authors: Hsu S , Chen Y , Roberson P , Marsh R , Pierce L , Moran J
Published: July 2007

Purpose: Skin dose assessment to the chest wall is important to ensure sufficient dose to the near‐surface target volume without undue skin reaction. Bolus is often used for a portion of the treatment course, but removed if clinically necessary because of skin toxicity. This study quantifies changes to the surface dose as a function of bolus material for conventional and IMRT techniques using a thermoluminescent dosimeter (TLD) extrapolation technique. Methods and Materials: Three types of bolus materials (2mm solid, 2mm fine mesh, and 3.2mm large mesh aquaplasts) were compared with Superflab (Med‐Tec). Surface dose measurements were performed using the Attix (parallel‐plate) chamber in a flat solid water phantom with the bolus materials for 10×10 cm2 and 10×20 cm2 jaw fields at 00, 450 and 700 incident angles. The Attix chamber measurements were used to validate the TLD extrapolation technique (0.89, 0.38, 0.15 mm thicknesses). TLDs were used to measure the surface dose on an anthropomorphic phantom for conventional and IMRT tangential fields. Results: Surface dose increased with increasing angles and field sizes. Oblique incidence has a larger influence on the surface when no bolus is present (from 20% to 48% for 10×10 cm2). The skin dose of solid 2mm aquaplast was larger than that of fine mesh aquaplast (22% for 10×10cm2−00 incidence, and 11% for 10×10cm2−700 incidence). Compared to conventional tangential fields, the skin dose for IMRT decreased ∼5%. For the conventional tangential fields, skin doses of fine mesh, solid, and large mesh aquaplasts were 21%, 11% and 9% less than that of superflab, respectively. For IMRT fields, skin doses were 22%, 12% and 10% less than that of superflab, respectively. Conclusion: For chest wall radiotherapy, the bolus type can be selected to compromise near‐skin target dose vs skin tolerance dose for optimal clinical outcome.
FAILURE-SENSITIVE ANALYSIS OF PARALLEL ALGORITHMS WITH CONTROLLED MEMORY ACCESS CONCURRENCY
Authors: GEORGIOU CHRYSSIS , RUSSELL ALEXANDER , SHVARTSMAN ALEXANDER A.
Published: July 2007

The abstract problem of using P failure-prone processors to cooperatively update all locations of an N-element shared array is called Write-All. Solutions to Write-All can be used iteratively to construct efficient simulations of PRAM algorithms on failure-prone PRAMS. Such use of Write-All in simulations is abstracted in terms of the iterative Write-All problem. The efficiency of the algorithmic solutions for Write-All and iterative Write-All is measured in terms of work complexity where all processing steps taken by the processors are counted. This paper considers determinitic solutions for the Write-All and iterative Write-All problems in the fail-stop synchronous CRCW PRAM model where memory access concurrency needs to be controlled. A deterministic algorithm of Kanellakis, Michailidis, and Shvartsman [16] efficiently solves the Write-All problem in this model, while controlling read and write memory access concurrency. However it was not shown how the number of processor failures f affects the work efficiency of the algorithm. The results herein give a new analysis of the algorithm [16] that obtain failure-sensitive work bounds, while retaining the known memory access concurrency bounds. Specifically, the new result expresses the work bound as a function of N, Pandf. Another contribution in this paper is the new failure-sensitive analysis for iterative Write-All with controlled memory access concurrency. This result yields tighter bounds on work (vs. [16]) for simulations of PRAM algorithms on fail-stop PRAMS.
ASPECTS OF BIOMOLECULAR COMPUTING
Authors: NAGY NAYA , AKL SELIM G.
Published: July 2007

This paper is intended as a survey of the state of the art of some branches of Biomolecular Computing. Biomolecular Computing aims to use biological hardware (biomare), rather than chips, to build a computer. We discuss the following three main research directions: DNA computing, membrane systems, and gene assembly in ciliates. DNA computing combines practical results together with theoretical algorithm design. Various search problems have been implemented using DNA strands. Membrane systems are a family of computational models inspired by the membrane structure of living cells. The process of gene assembly in ciliates has been formalized as an abstract computational model. Biomolecular Computing is a field in full development, with the promise of important results from the perspective of both Computer Science (models of computation) and Biology (understanding biological processes).
RADIATIVE QUARKONIUM DECAYS AND THE NMSSM HIGGS INTERPRETATION OF THE HyperCP Σ+→pμ+μ- EVENTS
Authors: MANGANO MICHELANGELO L. , NASON PAOLO
Published: July 2007

We study the potential of radiative decays of the ϒ1S and of the ϕ mesons to search for a light pseudoscalar Higgs boson, proposed as a possible interpretation of Σ+→pμ+μ- events observed by the HyperCP collaboration at Fermilab. We conclude that the detection of this signal should certainly be possible with the current CLEO ϒ1S data, and is within the reach of KLOE in at least part of the range of couplings suggested by the HyperCP findings.
QES SYSTEMS, INVARIANT SPACES AND POLYNOMIALS RECURSIONS
Authors: BRIHAYE YVES , NDIMUBANDI JEAN , MANDAL BHABANI PRASAD
Published: July 2007

Let us denote [Formula: see text], the finite-dimensional vector spaces of functions of the form ψ(x) = pn(x)+f(x)pm(x), where pn(x) and pm(x) are arbitrary polynomials of degree at most n and m in the variable x while f(x) represents a fixed function of x. Conditions on m, n and f(x) are found such that families of linear differential operators exist which preserve [Formula: see text]. A special emphasis is accorded to the cases where the set of differential operators represents the enveloping algebra of some abstract algebra. These operators can be transformed into linear matrix valued differential operators. In the second part, such types of operators are considered and a connection is established between their solutions and series of polynomials-valued vectors obeying three terms recurrence relations. When the operator is quasi-exactly solvable, it possesses a finite-dimensional invariant vector space. We study how this property leads to the truncation of the polynomials series.
Novel Use of Legendre Transformation in Field Theory and Many Particle Systems
Authors: Fukuda Reijiro , Komachiya Masahiro , Yokojima Satoshi , Suzuki Yoko , Okumura Ko , Inagaki Takeshi
Published: July 2007

The Legendre transformation is one of the ways to rewrite the theory by small number of selected variables. It leads naturally to the generalized action functional called the effective action and everything starts from this generating functional. It is applied to various problems of physics ranging from the relativistic field theory to the condensed matter physics. The main techniques used here are the on-shell expansion and the inversion method.

The scheme presented in this article is thus a generating functional formalism of the many particle systems.
Glassforming Liquids with Microscopic to Macroscopic Two-State Complexity
Authors: Angell C. A.
Published: July 2007

We review briefly the Adam-Gibbs-Goldstein approach to understanding the phenomenology of glassforming liquids and note three ways of scaling viscosity or relaxation time data which emphasize different aspects of the relationship between fragile and strong behavior in supercooling liquids. In all these cases, evolution from high temperature mobile to low temperature glassy states is smooth, the α-relaxation process being unimodal after the initial separation from the microscopic rattling mode. We then consider a series of cases where additional complexity enters in the form of new structural degrees of freedom which may be excited separately from the background structure modes and which are more slowly relaxing than the background modes. In first approximation, these may be considered as two-state systems superimposed on the normal glassformer background, and they may vary from (i) microscopic intramolecular degrees of freedom (such as a gauche-transisomerism) and microscopic intermolecular (such as unilateral hydrogen bonding to form molecular pairs) through (ii) mesoscopic cases in which large molecules can fold into tertiary structures (and the molecules themselves — proteins, RNAs — are mesoscopic glassforming systems), to (iii) macroscopic cases in which the glassforming liquid actually changes liquid phase through a first order transition.
Ideal Three-Mode Model for the Dynamics of Supercooled Liquids
Authors: Higuchi Mariko , Odagaki Takashi
Published: July 2007

We propose an ideal three-mode model which consists of two types of stochastic motions, nontrapped and trapped dynamics, and of an oscillation to explain the characteristics of the dynamical behavior of supercooled liquids. We calculate the dynamical structure factor and the generalized susceptibility and show that (1) the nontrapped stochastic motion gives rise to an α peak of the susceptibility, (2) the oscillation represents the β peak and (3) the trapped stochastic motion shows the characteristics of the fast process.