bluuebunny/crossref_metadata_2025 huggingface dataset:
Hardisty Cavern Storage Facility: Maximizing Process Equipment Utilization Through Innovative Automation Techniques
Authors: Neufeld Melvin , Miller Bruce A.
Published: December 2008

The Hardisty Cavern Facility at Hardisty, Alberta — consists of four underground salt caverns totalling 3.0 million barrels of petroleum products storage — was recently completed. This project is unique in that it integrates existing underground salt caverns into a significant North American crude oil transportation hub. Approximately 400 million barrels of oil move through this hub annually. This project utilizes existing caverns developed in the late 1960’s with significant upgrades and new infrastructure to integrate the Hardisty Cavern Facility into the crude oil transportation hub. This paper discusses the automation related innovations implemented and the challenges encountered during the course of the project. One example of innovation involves utilizing a single variable frequency drive (VFD) to perform multiple functions. Due to process requirements, the VFD was required to operate one or two cavern injection pumps. Electrical power grid constraints dictated that the VFD be used for starting and stopping the 1500 horsepower (1119 kW) pump motors. Process conditions also required that the pump motor loads be automatically transferred from VFD to the utility power grid without interruption to production. Operational flexibility was another key component of the facility automation requirements. Storage requirements for multiple petroleum products necessitated operator-selectable flow paths within the automation system. In addition, flexibility, safety, efficiency and maintainability requirements resulted in a distributed process philosophy across three separate process areas.
Simulation Tool to Select the Most Optimum Route for Pipeline Projects
Authors: Hirst Gary , Ruwanpura Janaka Y.
Published: December 2008

The decisions made during the process of selecting the route of pipeline are very critical to the project. Unfortunately, the decision is often complicated by the numerous variables that must be considered and the uncertainty of estimated costs. When choosing the pipeline route a project manager must balance the likely capital cost of the pipeline with the risks inherent in the chosen route. Ideally, a project manager would investigate numerous alternatives to fully explore the merits of various pipeline routes (including the level of risk) prior to making his final decision. This paper presents a project manager with a simulation tool to effectively and efficiently model the costs associated with various pipeline routes. The model is designed to be user friendly by replicating the usual decision-making process as much as possible. The model uses a graphical interface that promotes the rapid analysis of numerous alternatives and provides opportunities to investigate in detail the various aspects of a pipeline route. The model output includes a calculation of the costs of the alternative, a statistical analysis of the risks of the project and information that can be used to establish the confidence level of a pipeline target price.
Prediction of Corrosion Defect Failure Pressure for Finite Length Defects
Authors: Cronin Duane S.
Published: December 2008

Corrosion defects commonly occur on operating pipelines due to a loss of protection in a corrosive environment. These defects require practical and accurate assessment, particularly for older pipeline systems, to determine the need for remediation or allow for continued operation. Previous research has shown that appropriate application of full three-dimensional finite element analysis, and newly developed analytical approaches, can provide very accurate predictions of failure pressure but require detailed material and geometric data. Although this is important, a simpler method that allows for efficient evaluation of large amounts of data is also desirable. A method has been developed from an existing analytical solution by assuming a defect can be characterized in terms of the total defect length, and a constant defect depth equal to the maximum defect depth. In general this produces a conservative estimate of the material loss. This finite-length defect solution is in good agreement with experimental data for idealized defects, and provides reasonable predictions of burst pressure, with a minimum amount of data, when applied to real corrosion defects.
Prediction of Ductile Failure in Metal Structures Based on Thermodynamics of Irreversible Process
Authors: Lukyanov Alexander A.
Published: December 2008

The objective of the work presented in this paper is to generate a thermodynamically consistent coupled thermoelastic-plastic damage model of solid media at a macroscopic level. The model is based on the thermodynamics of irreversible processes and the assumption that damage within a continuum can be represented as a damage tensor ωij [1], [4]. This allows for definition of two scalars that are ω = ωkk / 3 (the volume damage) [2], [3] and α = ωij′ωij′ (a norm of the damage tensor deviator ωij′ = ωij − ωδij [4]. The parameter ω describes the accumulation of micro-pore type damage (which may disappear under compression) and the parameter α describes the shear related damage. The parameter ω may be considered as a volume content of micropores in the material. In the damage-free material we have ω = α = 0; if damage is accumulated, ω and α increase in such a manner that they remain less than one. The prediction of void growth is based on work by Tuler-Butcher [4]. This damage evolution is then coupled to a rate and temperature dependent deviatoric plasticity model. The criterion for failure is the entropy criterion based on a critical value of a specific dissipation function [4]. Performance of the model is illustrated by few numerical examples.
Re-Assessment Survey of Large Diameter Pipelines Using Compact Multi-Purpose Inline Inspection Tools
Authors: Bekker Mikhail Viktorovich , Beuker Thomas , Thuenemann Uwe , Paeper Steffen
Published: December 2008

Large diameter pipelines of 48” and 56” traverse the Ukraine. These pipelines are the life-line for the Russian gas transit to high demand European Union (EU) markets. The high economic impact to several European regions and the complicated legislation of these pipeline systems reduces the operators’ ability to change operating conditions to better suit in-line inspection. Ukrtransgaz requested a reliable and compact inspection tool able to negotiate 1.5D bends. Thirty degree (30°) mitre bends and demanding elevation changes in the range of 1500m (4921ft) also had to be considered. The high economic impact of the pipeline systems did not allow Ukrtransgaz to reduce the high flow speed of the gas, which is more than 10 m/s (22.2mph), during the inspection. In combination with the before-mentioned elevation profile, an inspection tool with active speed control was required. As part of the planned re-assessment survey, an XYZ mapping inspection relying on an inertial navigation system was also required. The inspection solutions provided by ROSEN were multipurpose tools providing MFL technology, an XYZ mapping module and active speed control in a single body. It will be discussed in this paper how the miniaturization of electronics and computer technology is not only a key point for small diameter tools, but also essential to meet the demanding targets of inspecting large diameter gas lines. Breaking with the paradigm, that large pipe provides enough internal space, was the basis in accomplishing the demands of the operator.
Application of Brillouin Fiber Optic Sensors to Monitor Pipeline Integrity
Authors: Tennyson R. C. , Morison W. D. , Colpitts B. , Brown A.
Published: December 2008

This paper describes the application of Brillouin fiber optic sensors to monitor pipeline integrity in terms of third party intrusion, leak detection, and ground movement. Brillouin sensors provide a means for continuous monitoring of strain and temperature distributions over distances of about 25km. The optical fibers can be bonded to the pipeline or buried in close proximity to the pipe. Third party intrusion is detected by strain anomalies caused by vehicles or persons in close proximity to the sensor located at some depth below the surface. Leaks from oil or gas pipelines are detected by thermal anomalies in the temperature profiles. Pipeline movement can also be detected using this system for existing and new pipeline installations. Applications include northern pipelines, high consequence areas, river crossings and fault lines.
Petroleum Pipe Leakage Detection and Location Embeded in SCADA
Authors: Wang Likun , Li Jian , Peng Ke , Jin Shijiu , Li Zhuang
Published: December 2008

With the increase of the age of the transport oil pipeline and the man-made destruction to pipeline, leaks are often found. The system for pipeline leakage detection and location must be established to find leakage and locate the leak positions to reduce serious environmental pollution and economic loss caused by leakage. The negative pressure wave method is an effective way to locate the leak position, because over 98 percent pipe leakage in China is paroxysmal. There is a SCADA (supervisory control and data acquisition) system to monitor operation for long transport petroleum pipe, but the function of leakage detection and location is not included in existing SCADA system in China. This paper used Dynamic Data Exchange (DDE) method to obtain pipe operation parameters such as pressure, flow rate, temperature, bump current, valve position and so on from the SCADA system. That takes full advantage of the abundant data collection function of the SCADA system to provide data for leakage detection and location. The wavelet packet analysis-based fault diagnosis method can directly use the change of parameters such as energy of frequency component to detect faults without system model. In the paper, a wavelet packet analysis-based characteristic extraction method is used to extract the characteristic information of leak pressure signals. The eigenvector indexes along with the parameters obtained from the SCADA system can be used to avoid false alarms. Wavelet analysis was used to locate leak positions accurately in this paper. Such a wavelet analysis-based leakage detection and location scheme embedded in the SCADA system has been successfully applied to a pipeline in PetroChina. Practical run demonstrated its well effect.
The Design of an Ultrasonic Phased Array System on Pipelines’ Weld Inspection
Authors: Chen Shili , Song Guangde , Jin Shijiu , Zhan Xianglin
Published: December 2008

Phased arrays generate ultrasonic waves by using recisely-defined time delays for each element in an ultrasonic array group, this permits constructive and destructive interference of the wavefronts to form the pre-defined beam. So, ultrasonic phased arrays are well suited to weld inspections. First, beams can be multiplexed across the array, in what is called “electronic scanning”. This permits very rapid inspections of components, typically an order of magnitude faster than a single transducer raster scan. Second, the beam can be swept through a range of angles without moving the array; this is called “beam steering”, and the inspections are typically called “azimuthal” scans or “sectorial” scans. Before weld inspecting, the time delays between elements were computed using a specific model and compared to experimental delays obtained using through transmission tests. This paper describes the application of phased array on pipelines’ weld inspection. The detail hardware designs of linear phased arrays system and the summary of system performance are presented. This inspection system includes eight ultrasonic signal transmitting and receiving circuit units, which are used to control time sequence of ultrasonic beam and select channel used for waves construction, and amplify the received ultrasonic signal. Each unit is connected with 16 probe elements (total 128 elements in this system), and can receive 4-way ultrasonic signals (channel selection is done by RF switching). Additional performance is gained by intensively using FPGA (Field Programmable Gate Arrays) technology for memory and delay counters. Since the working frequency or FPGA is 100MHz, the delay time less than 10 ns is realized by analogue delay line. This system not only has the functions of conventional ultrasonic inspector, but also can display the defect shape and its size on the screen.
A Simple Two-Phase Frictional Multiplier Calculation Method
Authors: Awad M. M. , Muzychka Y. S.
Published: December 2008

In this paper, a simple method for calculating two-phase frictional multiplier for total flow assumed liquid in the pipe φlo2 is presented. The homogeneous model is used to calculate the fluid properties (density and viscosity). The Churchill model is used to define the Fanning friction factor to take into account the effect of the mass flux on φlo2. Effect of stream pressure on φlo2 is also investigated. It is found that φlo2 decreases with increasing the stream pressure at a given mass quality and reaches 1 at the critical pressure. On the other hand, it is found that φlo2 increases with increasing the mass flux at a given mass quality. Comparison with other existing correlations for calculating φlo2 such as the Wallis correlation based on the homogeneous model without mass effect on φlo2, the Martinelli-Nelson correlation, the Chisholm correlation, and the Friedel correlation is presented. When the mass flux value becomes low, the effect of mass flux on φlo2 becomes small and present correlation approaches the Wallis correlation. Both the present correlation and the Wallis correlation approach the maximum two-phase frictional multiplier in a smooth consistent manner while the other correlations show a peaking effect at high mass qualities. The Friedel correlation shows better agreement with the present correlation than both the Martinelli-Nelson correlation and the Chisholm correlation. Comparison with results from other experimental test facilities for calculating φlo2 is also presented. Comparison with other experimental data shows better agreement with the present correlation than the Martinelli-Nelson correlation.
Simulation of Cold Bends by Finite Element Method
Authors: Behbahanifard M. , Cheng J. J. R. , Murray D. W. , Zhou Joe , Adams K. , Yoshizaki K. , Fukuda N. , Como M. , Cerelli E.
Published: December 2008

A composite finite element model for cold bend simulation of energy pipelines is presented in this paper. Four-node shell elements with material and geometric nonlinearity are used to model a pipe in straight condition. An elastic pipe, having the same nodal coordinates as the main pipe along with elastic radial links are used as a tool to prevent local buckling and ovalization of the main pipe during the cold bend process. By dividing the elastic pipe into series of rings along the axis of the pipe and by conducting a four-step procedure, residual curvature is developed in a specific segment of a pipe. Based on the proposed concept, different methods of cold bending are discussed and the results are presented. University of Alberta cold bend trials were used to validate the proposed finite element model. The moment-curvature response, pattern of imperfections, and distribution of maximum residual strains are obtained by the finite element model and compared with the test results.
Telluric Compensation for Pipeline Test Station Survey on the Alliance Pipeline System
Authors: Carlson Lorne , Dorman Brent , Place Trevor
Published: December 2008

Geomagnetically induced currents (GIC’s), or telluric currents, can have a profound effect on pipe-to-soil measurements during close interval and test station surveys. Previous studies have investigated how to improve close interval survey data with excellent results. This paper discusses a study on improving test station survey data collected on the Alliance pipeline system and the limitations of the methods used.
Monitoring Leakages on Oil Production Offloading at Open Seas Using Statistics Associated With Mass Balance Methods
Authors: Moura Carlos H. W. , Sampaio Dirceu S. , de Lacerda Igor M. , Selli Marcelo F.
Published: December 2008

With the increasing number of former VLCC (Very Large Crude Cargos) transformed into FPSOs worldwide, and its associated inherent oil production exportation characteristics to shuttle tankers, where very large flow rates are combined to the use of short and large diameters exporting lines, in many cases involving the use of hoses instead of flexible pipelines, and the obviously very sensitive environment, considering the execution of this transference in open seas, where losses for even a small period, regarded the involved exportation capacity means a huge spillage, with all its legal and image associated impacts, the challenge to identify and test technologies able to carry out the most effective leakage detection in this scenario was placed to PETROBRAS technical team, as consequence of rules demanding the installation of such systems stated by Brazilian Environmental Agencies. The proposal of this paper is to show the leakage detection solution based on a hybrid method combining mass balance along with statistical treatment adopted for monitoring the oil production offloading from the FPSO - MARLIM SUL, in the Campos Basin, Brazil, to a dynamically positioned shuttle vessel throughout a 150 meters, 20” diameter hose designed for a flow rate of 8.000 m3 per hour. A short description of this production system is provided, the operational principles of the adopted leakage system are depicted, its architecture is detailed, and the reasons that ended up leading PETROBRAS to adopt this technology amongst those others also considered are presented. Finally, comments about the installation, start-up and tuning, and considerations about the system observed behavior are made.
Commissioning and implementation of a stereotactic conformal radiotherapy technique using a general‐purpose planning system
Authors: Mosleh‐Shirazi M. Amin , Hansen Vibeke N. , Childs Peter J. , Warrington Alan P. , Saran Frank H.
Published: December 2008

The purpose of this paper is to report on commissioning and clinical implementation of a customized system for pediatric stereotactic conformal radiotherapy (SCRT). The system is based on the Pinnacle treatment‐planning system and its interfaces with other equipment: (1) Beam models were optimized for our compact blocking system and a new LINAC. (2) Three CT‐to‐density conversion tables were evaluated, one using tabulated data for a commercial phantom, the second including additional points from the manufacturer's data for the inserts in an in‐house phantom, and the third using measured densities for the in‐house phantom materials combined with tabulated data for the commercial phantom. (3) Blocks were transferred to a computerized block cutter using in‐house software that extracted the block shape from the export file and custom‐fitted the additional necessary shapes. (4) In the absence of a DICOM RT Image link, a method based on screen data capture was used to export digitally reconstructed radiographs (DRRs) to two portal imaging systems for treatment verification. Lens shielding by multileaf collimation in the anterior‐posterior isocenter verification field was investigated. (1) Computed dose distributions using the beam models agreed with measurements well within published acceptability criteria. A difference of up to 1.0 mm was measured between the beam's eye views of aperture blocks and computed 50% isodose contours for a dose calculation grid. (2) The third table, which included measured densities, improved the accuracy of the calculated isocenter dose by up to 0.5% in typical patient SCRT treatments and up to 1.0% in a phantom with 5‐cm diameter inhomogeneity inserts. (3) The block export and customization process was shown to introduce no additional uncertainty. A 1‐mm block production uncertainty was measured using film dosimetry on six blocks. (4) The DRR transfer method did not introduce uncertainty into the process. Verification field shielding reduced lens dose by 12 to 15 times. In conclusion, this customized system for planning and verification of pediatric SCRT provides a high level of precision as well as reasonable practical efficiency.

PACS numbers: 87.53.Kn, 87.53.Ly, 87.53.Oq, 87.53.Tf, 87.53.Uv
Clinical validation of the normalized mutual information method for registration of CT and MR images in radiotherapy of brain tumors
Authors: Veninga Theo , Huisman Henkjan , van der Maazen Richard W. M. , Huizenga Henk
Published: December 2008

Image registration integrates information from different imaging modalities and has the potential to improve determination of target volume in radiotherapy planning. This paper describes the implementation and validation of a 3D fully automated registration procedure in the process of radiotherapy treatment planning of brain tumors. Fifteen patients with various brain tumors received computed tomography (CT) and magnetic resonance (MR) brain imaging before the start of radiotherapy. First, the normalized mutual information (NMI) method was used for image registration. Registration accuracy was estimated by performing statistical analysis of coordinate differences between CT and MR anatomical landmarks along the x‐, y‐ and z‐axes. Second, a visual validation protocol was developed to validate the quality of individual registration solutions, and this protocol was tested in a series of 36 CT‐MR registration procedures with intentionally applied registration errors. The mean coordinate differences between CT and MR landmarks along the x‐ and y‐axes were in general within 0.5 mm. The mean coordinate differences along the z‐axis were within 1.0 mm, which is of the same magnitude as the applied slice thickness in scanning. In addition, the detection of intentionally applied registration errors by employment of a standardized visual validation protocol resulted in low false‐negative and low false‐positive rates. Application of the NMI method for the brain results in excellent automatic registration accuracy, and the method has been incorporated into the daily routine at our institution. A standardized validation protocol ensures the quality of individual registrations by detecting registration errors with high sensitivity and specificity. This protocol is proposed for the validation of other linear registration methods.

PACS numbers: 87.53.Xd, 87.57.Gg
Compensators: An alternative IMRT delivery technique
Authors: Chang Sha X. , Cullip Timothy J. , Deschesne Katharin M. , Miller Elizabeth P. , Rosenman Julian G.
Published: December 2008

Seven years of experience in compensator intensity‐modulated radiotherapy (IMRT) clinical implementation are presented. An inverse planning dose optimization algorithm was used to generate intensity modulation maps, which were delivered via either the compensator or segmental multileaf collimator (MLC) IMRT techniques. The in‐house developed compensator‐IMRT technique is presented with the focus on several design issues. The dosimetry of the delivery techniques was analyzed for several clinical cases. The treatment time for both delivery techniques on Siemens accelerators was retrospectively analyzed based on the electronic treatment record in LANTIS for 95 patients. We found that the compensator technique consistently took noticeably less time for treatment of equal numbers of fields compared to the segmental technique. The typical time needed to fabricate a compensator was 13 min, 3 min of which was manual processing. More than 80% of the approximately 700 compensators evaluated had a maximum deviation of less than 5% from the calculation in intensity profile. Seventy‐two percent of the patient treatment dosimetry measurements for 340 patients have an error of no more than 5%. The pros and cons of different IMRT compensator materials are also discussed. Our experience shows that the compensator‐IMRT technique offers robustness, excellent intensity modulation resolution, high treatment delivery efficiency, simple fabrication and quality assurance (QA) procedures, and the flexibility to be used in any teletherapy unit.

PACS numbers: 87.53Mr, 87.53Tf
LINAC‐based stereotactic radiosurgery for treatment of trigeminal neuralgia
Authors: Gerbi Bruce J. , Higgins Patrick D. , Cho Kwan H. , Hall Walter A.
Published: December 2008

Trigeminal neuralgia (TN) is a disabling pain condition that has classically been treated using either surgical or medical techniques. Several researchers have shown that stereotactically delivered radiation can be an effective tool in the amelioration of this condition. For these studies, the Gamma Knife was used to deliver the radiation treatment. The target location was designated as the proximal nerve at the root entry zone, and doses greater than 70 Gy to the maximum point in a single fraction were found to be effective in controlling pain in 80% of the patients treated. LINAC‐based stereotactic radiosurgery has been notably absent from the treatment of TN, even though it has many similarities to Gamma Knife‐based stereotactic radiosurgery.

The aim of this paper is to describe our LINAC‐based stereotactic technique for treatment of TN. We also compare treatment of TN using our technique to that using the Gamma Knife. We found that a LINAC‐based treatment of TN can be accomplished with accuracy comparable to treatments delivered using the Gamma Knife. The dose distributions are essentially equivalent for the two treatment approaches. The LINAC‐based system is easy to plan and offers the ability to reduce the involvement of sensitive structures from the treatment fields as well as the Gamma Knife system does. A disadvantage of the LINAC‐based system is the time involved for treatment.

PACS number: 87.53.Tf 87.56.Da
Quality assurance: Fundamental reproducibility tests for 3D treatment‐planning systems
Authors: Able Charles M. , Thomas Michael D.
Published: December 2008

The use of image‐based 3D treatment planning has significantly increased the complexity of commercially available treatment‐planning systems (TPSs). Medical physicists have traditionally focused their efforts on understanding the calculation algorithm; this is no longer possible. A quality assurance (QA) program for our 3D treatment‐planning system (ADAC Pinnacle3) is presented. The program is consistent with the American Association of Physicists in Medicine Task Group 53 guidelines and balances the cost‐versus‐benefit equation confronted by the clinical physicist in a community cancer center environment. Fundamental reproducibility tests are presented as required for a community cancer center environment using conventional and 3D treatment planning. A series of nondosimetric tests, including digitizer accuracy, image acquisition and display, and hardcopy output, is presented. Dosimetric tests include verification of monitor units (MUs), standard isodoses, and clinical cases. The tests are outlined for the Pinnacle3 TPS but can be generalized to any TPS currently in use. The program tested accuracy and constancy through several hardware and software upgrades to our TPS. This paper gives valuable guidance and insight to other physicists attempting to approach TPS QA at fundamental and practical levels.

PACS numbers: 87.53.Tf, 87.53.Xd
Effects of field parameters on IMRT plan quality for gynecological cancer: A case study
Authors: Fung Albert Y.C. , Enke Charles A. , Ayyangar Komanduri M. , Thompson Robert B. , Zhen Weining , Raman Natarajan V. , Djajaputra David , Li Sicong , Nehru Ramasamy M. , Pillai Sushakumari , Sourivong Paul , Headley Mary , Yager Ann L.
Published: December 2008

Traditional external beam radiotherapy of gynecological cancer consists of a 3D, four‐field‐box technique. The radiation treatment area is a large region of normal tissue, with greater inhomogeneity over the treatment volume, which could benefit more with intensity‐modulated radiation therapy (IMRT). This is a case report of IMRT planning for a patient with endometrial cancer. The planning target volume (PTV) spanned the intrapelvic and periaortic lymph nodes to a 33‐cm length. Planning and treatment were accomplished using double isocenters. The IMRT plan was compared with a 3D plan, and the effects of field parameters were studied. Delineated anatomical contours included the intrapelvic nodes (PTV), bone marrow, small bowel, bladder, rectum, sigmoid colon, periaortic nodes (PTV), spinal cord, left kidney, right kidney, large bowel, liver, and tissue (excluding the PTVs). Comparisons were made between IMRT and 3D plans, 23‐MV and 6‐MV energies, zero and rotated collimator angles, different numbers of segments, and opposite gantry angle configurations. The plans were evaluated based on dose‐volume histograms (DVHs). Compared with the 3D plan, the IMRT plan had superior dose conformity and spared the bladder and sigmoid colon embedded in the intrapelvic nodes. The higher energy (23 MV) reduced the dose to most critical organs and delivered less integral dose. Zero collimator angles resulted in a better plan than “optimized” collimator angles, with lower dose to most of the normal structures. The number of segments did not have much effect on isodose distribution, but a reasonable number of segments was necessary to keep treatment time from being prohibitively long. Gantry angles, when evenly spaced, had no noticeable effect on the plan. The patient tolerated the treatment well, and the initial complete blood count was favorable. Our results indicated that large‐volume tumor sites may also benefit from precise conformal delivery of IMRT.

PACS numbers: 87.53.Kn, 87.53.Tf
Density scaling artifacts in dosimetry calculations
Authors: Dickof Peter
Published: December 2008

Quality assurance dosimetry often requires the comparison of measured doses with those calculated by a treatment‐planning system for phantoms of density other than 1.000 g/cm3. The presence of an artifact in the Pinnacle3 treatment‐planning system can lead to systematic errors in such cases.a These errors are also present, although reduced in magnitude, in heterogeneous media.

PACS: 87.53.Bn, 87.53.Xd
Treatment‐planning considerations for prostate implants with the new linear RadioCoil™ brachytherapy source
Authors: Meigooni Ali S. , Awan Shahid B. , Rachabatthula Venkata , Koona Rafiq A.
Published: December 2008

Recently, various linear source models, for example, RadioCoil™, have been introduced to overcome the shortcomings of traditional “seed” type interstitial prostate brachytherapy implants, such as migration and clumping of the seeds. However, the existing prostate treatment‐planning systems have not been updated to perform dose calculation for implants with linear sources greater than 1.0 cm in length. In these investigations, two new models are developed for 3D dose calculation for a prostate implant with linear brachytherapy sources using the commercially available treatment‐planning systems. The proposed models are referred to as the linear‐segmented source (LSS) model and the point‐segmented source (PSS) model. The calculated dose distributions obtained by these models for a single linear source have been validated by their comparison with the Monte Carlo–simulated data. Moreover, these models were used to calculate the dose distributions for a multilinear source prostate implant, and the results were compared to “seed” type implants. The results of these investigations show that the LSS model better approximates the linear sources than the PSS model. Moreover, these models have shown a better approximation of the dose distribution from a linear source for 0.5 cm source segments as compared to 1.0 cm source segments. However, for the points close to the longitudinal axis of the source located outside the region bounded by the active length, both models show differences of approximately . These deficiencies are attributed to the limitations of the TG43 formalism for elongated sources.

PACS number: 87.53.‐j
Evaluation of dose delivery accuracy of Gamma Knife by polymer gel dosimetry
Authors: Watanabe Yoichi , Akimitsu Tomohide , Hirokawa Yutaka , Mooij Rob B. , Perera G. Mark
Published: December 2008

The BANG™ polymer gel dosimeter was used to evaluate 3D absorbed dose distributions in tissue delivered with Gamma Knife stereotactic radiosurgery systems. We compared dose distributions calculated with Leksell GammaPlan (LGP) treatment‐planning software with dose distributions measured with the polymer gel dosimeter for single‐shot irradiations. Head‐sized spherical glass vessels filled with the polymer gel were irradiated with Gamma Knife. The phantoms were scanned with a 1.0T MRI scanner. The Hahn spin‐echo sequence with two echoes was used for the MRI scans. Calibration relations between the spin‐spin relaxation rate and the absorbed dose were obtained by using small cylindrical vials, which were filled with the polymer gel from the same batch as for the spherical phantom. We made voxel‐by‐voxel comparisons of measured and calculated dose distributions for dose matrix elements. With the 3D dose data we calculated the tumor control probability (TCP) and normal tissue complication probability (NTCP) for a simple model. For the maximum dose of 100 Gy, the mean and one standard deviation of differences between the measured and the calculated doses were the following: Gy, and for 8‐mm, 14‐mm, and 18‐mm collimators, respectively. Tumor control probability values for measurements were smaller than the calculations by 0% to 7%, whereas NTCP values were larger by 7% to 24% for four of six experiments.

PACS numbers: 87.53.‐j, 87.53.Dq, 87.53.Ly
Edge‐detection of the radiation field in double exposure portal images using a curve propagation algorithm
Authors: Lasserre Patricia , Cutt Bryce , Moffat James
Published: December 2008

An accurate detection of the radiation field is crucial to 3D conformal radiotherapy (3D‐CRT). Automated techniques to detect the field edges on double exposure portal images have previously focused on thresholding techniques. In this paper, we present a new approach based on a curve propagation technique (the Fast Marching method) which proves to be more effective at detecting the radiation field than its thresholding counterpart. The comparison of both techniques in terms of computational speed and effectiveness of the detection is presented using complex images with non‐homogeneous intensity levels inside the radiation field, and gradual variations in intensity level at the field boundaries. Results show that our Fast Marching method is easier to automate, and converges faster to the boundaries of the segmented radiation field. The computation time of the Fast Marching technique is five times faster in typical portal images.

PACS numbers: 87.53.Oq, 87.57.Nk, 87.57.‐s.
A novel algorithm for initial lesion detection in ultrasound breast images
Authors: Yap Moi Hoon , Edirisinghe Eran A. , Bez Helmut E.
Published: December 2008

This paper proposes a novel approach to initial lesion detection in ultrasound breast images. The objective is to automate the manual process of region of interest (ROI) labeling in computer‐aided diagnosis (CAD). We propose the use of hybrid filtering, multifractal processing, and thresholding segmentation in initial lesion detection and automated ROI labeling. We used 360 ultrasound breast images to evaluate the performance of the proposed approach. Images were preprocessed using histogram equalization before hybrid filtering and multifractal analysis were conducted. Subsequently, thresholding segmentation was applied on the image. Finally, the initial lesions are detected using a rule‐based approach. The accuracy of the automated ROI labeling was measured as an overlap of 0.4 with the lesion outline as compared with lesions labeled by an expert radiologist. We compared the performance of the proposed method with that of three state‐of‐the‐art methods, namely, the radial gradient index filtering technique, the local mean technique, and the fractal dimension technique. We conclude that the proposed method is more accurate and performs more effectively than do the benchmark algorithms considered.

PACS numbers: 87.57.Nk
Radiographic film dosimetry for IMRT fields in the near‐surface buildup region
Authors: Roberson Peter L. , Moran Jean M. , Kulasekere Ravi
Published: December 2008

Radiographic film dosimetry provides fast, convenient 2‐D dose distributions, but is challenged by the dependence of film response on scatter conditions (i.e., energy dependence). Verification of delivered dose in the surface buildup region is important for intensity modulated radiation therapy (IMRT) when volumes of interest encroach on these regions (e.g., head/neck, breast). The current work demonstrates that film dosimetry can accurately predict the dose in the buildup region for IMRT, since 1) film dosimetry can be performed with sufficient accuracy for small fields and 2) IMRT is delivered by a series of “small” segments (step and shoot IMRT). This work evaluates the accuracy of X‐OMAT V (XV) and Extended Dose Range (EDR) film for measurements from 2 mm to 15 mm depths for small fields and clinical IMRT beams. Film measurements have been compared to single point measurements made with a stereotactic diode and parallel plate ionization chamber (P11) and thermoluminescent dosimeters (TLD) at various depths for square (diode, P11) and IMRT (diode, TLD) fields. Film calibration was performed using an 8‐field step exposure on a single film at 5 cm depth, which has been corrected to represent either small field or large field depth dependent film calibration techniques. Up to 10% correction for film response variation as a function of depth was required for measurements in the buildup region. A depth‐dependent calibration can sufficiently improve the accuracy for IMRT calculation verification (i.e., uncertainty). A small field film calibration technique was most appropriate for IMRT field measurements. Improved buildup region dose measurements for clinical IMRT fields promotes improved dose estimation performance for (inverse) treatment planning and allows more quantitative treatment delivery validation.

PACS numbers: 87.53.‐j, 87.53.Dq
FBX aqueous chemical dosimeter for measurement of virtual wedge profiles
Authors: Semwal Manoj K. , Bansal Anil K. , Thakur Pradeep K. , Vidyasagar Pandit B.
Published: December 2008

We investigated the ferrous sulfate–benzoic acid–xylenol orange (FBX) aqueous chemical dosimeter for measurement of virtual (dynamic) wedge profiles on a linear accelerator. The layout for irradiation of the FBX‐filled tubes mimicked a conventional linear detector array geometry. A comparison of the resulting measurements with film‐measured profiles showed that, in the main beam region, the difference between the FBX system and the film system was within and that, in the penumbra region, the difference varied from to in terms of positional equivalence, depending on the size of the dosimeter tubes. We thus believe that the energy‐independent FBX dosimetry system can measure virtual wedge profiles with reasonable accuracy at reasonable cost. However, efficiency improvement is required before this dosimetry system can be accepted into routine practice.

PACS numbers: 87.53.‐j, 87.53.Dq, 87.53.Mr, 87.53.Xd, 87.66.Ff
Optimal acquisition parameter selection for CT simulators in radiation oncology
Authors: Liu Ruijie Rachel , Prado Karl L , Cody Dianna
Published: December 2008

The purpose of this study was to identify optimal CT acquisition parameter settings for each make and model of scanners used in a large Radiation Oncology (RO) Department, considering the special requirements of CT simulation. Two CT phantoms were used to evaluate the image quality of the five different multichannel CT scanners using helical scan mode. We compared the effects of various pitch, detector configurations, and rotation time parameters on image artifacts, and on spatial and contrast resolution. We found that helical artifact was closely related to pitch and detector configuration settings. This artifact was scanner‐specific and generally more obvious when the channel width or detector collimation was equal to the image thickness. Different acquisition parameter settings produced slight differences in observed high‐ and low‐contrast resolution. Short rotation time degraded image quality for certain scanners, but only slightly, while other rotation times, such as 0.75 sec/rotation and above, had no obvious effect on resolution. An optimized combination of acquisition parameters was determined for each scanner make and model, based on phantom image quality and other considerations for clinical applications. This information may be directly useful for physicists whose CT simulation scanners match one of the five examined in this study. If not, the strategy reported here may be used as a guide to perform a similar evaluation of the scanner.

PACS numbers: 87.57.Ce, 87.57.qp, 87.55.Gh, 87.57.C‐
Glandular radiation dose in tomosynthesis of the breast using tungsten targets
Authors: Sechopoulosa Ioannis , D'Orsi Carl J.
Published: December 2008

With the advent of new detector technology, digital tomosynthesis imaging of the breast has, in the past few years, become a technique intensely investigated as a replacement for planar mammography. As with all other x‐ray–based imaging methods, radiation dose is of utmost concern in the development of this new imaging technology. For virtually all development and optimization studies, knowledge of the radiation dose involved in an imaging protocol is necessary. A previous study characterized the normalized glandular dose in tomosynthesis imaging and its variation with various breast and imaging system parameters. This characterization was performed with x‐ray spectra generated by molybdenum and rhodium targets. In the recent past, many preliminary patient studies of tomosynthesis imaging have been reported in which the x‐ray spectra were generated with x‐ray tubes with tungsten targets. The differences in x‐ray distribution among spectra from these target materials make the computation of new normalized glandular dose values for tungsten target spectra necessary. In this study we used previously obtained monochromatic normalized glandular dose results to obtain spectral results for twelve different tungsten target x‐ray spectra. For each imaging condition, two separate values were computed: the normalized glandular dose for the zero degree projection angle (), and the ratio of the glandular dose for non‐zero projection angles to the glandular dose for the zero degree projection (the relative glandular dose, RGD(α)). It was found thatis higher for tungsten target x‐ray spectra when compared withvalues for molybdenum and rhodium target spectra of both equivalent tube voltage and first half value layer. Therefore, thefor the twelve tungsten target x‐ray spectra and different breast compositions and compressed breast thicknesses simulated are reported. The RGD(α) values for the tungsten spectra vary with the parameters studied in a similar manner to that found for the molybdenum and rhodium target spectra. The surface fit equations and the fit coefficients for RGD(α) included in the previous study were also found to be appropriate for the tungsten spectra.

PACS numbers: 87.57.uq
ON THE UNIQUENESS OF D = 11 INTERACTIONS AMONG A GRAVITON, A MASSLESS GRAVITINO AND A THREE-FORM II: THREE-FORM AND GRAVITINI
Authors: CIOROIANU EUGEN-MIHĂIŢĂ , DIACONU EUGEN , SĂRARU SILVIU CONSTANTIN
Published: December 2008

The interactions that can be introduced between a massless Rarita–Schwinger field and an Abelian three-form gauge field in 11 space–time dimensions are analyzed in the context of the deformation of the "free" solution of the master equation combined with local BRST cohomology. Under the hypotheses of smoothness of the interactions in the coupling constant, locality, Poincaré invariance, Lorentz covariance, and the presence of at most two derivatives in the Lagrangian of the interacting theory (the same number of derivatives as in the free Lagrangian), we prove that there are neither cross-couplings nor self-interactions for the gravitino in D = 11. The only possible term that can be added to the deformed solution to the master equation is nothing but a generalized Chern–Simons term for the three-form gauge field, which brings contributions to the deformed Lagrangian, but does not modify the original, Abelian gauge transformations.
SOME BIANCHI TYPE COSMOLOGICAL MODELS IN LYRA GEOMETRY
Authors: SINGH J. K.
Published: December 2008

A class of nonstatic solutions for Einstein field equations has been investigated in the context of Bianchi type-V space–time in the theory based on Lyra's geometry in Gauss normal gauge and in the presence of an attractive massive scalar field. The results have been studied through various physical and geometrical parameters. The energy conditions of the model have also been verified.
NEW ACTIONS FOR SELF-DUAL FIELDS IN 2D AND 3D
Authors: ABREU E. M. C. , CALIL A. , GRIGORIO L. S. , GUIMARAES M. S. , WOTZASEK C.
Published: December 2008

New actions in D = 2 and D = 3 are proposed that are dual equivalent to known theories displaying well-defined chirality and helicity, respectively, along with new interpolating actions mapping continuously through the original dualities. The new chiral action in D = 2 is a second-order theory displaying the chiral constraint dynamically. In D = 3 the helicity constraint is imposed a la Siegel displaying a continuous mapping between the Maxwell–Chern–Simons and the self-dual model. It is also shown that the resulting theories introduce new versions of the Hull noton to take care of the symmetry aspects of the original models. The new interpolating formulation is then reexamined as a condensed phase for the discussion of duality under the light of the dual mechanisms — Julia–Toulouse and Higgs — establishing new interpolating actions in the dilute phase, according to these mechanisms.
Expressiveness and complexity of XML publishing transducers
Authors: Fan Wenfei , Geerts Floris , Neven Frank
Published: December 2008

A number of languages have been developed for specifying XML publishing, that is, transformations of relational data into XML trees. These languages generally describe the behaviors of a middleware controller that builds an output tree iteratively, issuing queries to a relational source and expanding the tree with the query results at each step. To study the complexity and expressive power of XML publishing languages, this article proposes a notion of
publishing transducers
, which generate XML trees from relational data. We study a variety of publishing transducers based on what relational queries a transducer can issue, what temporary stores a transducer can use during tree generation, and whether or not some tree nodes are allowed to be virtual, that is, excluded from the output tree. We first show how existing XML publishing languages can be characterized by such transducers, and thus provide a synergy between theory and practice. We then study the membership, emptiness, and equivalence problems for various classes of transducers. We establish lower and upper bounds, all matching, ranging from PTIME to undecidable. Finally, we investigate the expressive power of these transducers and existing languages. We show that when treated as relational query languages, different classes of transducers capture either complexity classes (e.g., PSPACE) or fragments of datalog (e.g., linear datalog). For tree generation, we establish connections between publishing transducers and logical transductions, among other things.