bluuebunny/crossref_metadata_2025 huggingface dataset:
Emergency Control of Vehicle Platoons: System Operation and Platoon Leader Control
Authors: Hoberock L. L. , Rouse R. J.
Published: July 2010

In the work herein and in [1], an automatic control concept is developed for both normal and emergency longitudinal regulation of high density strings of vehicles with velocities in the range 50 to 90 mph (80 to 144 km/hr). Under this concept, a vehicle string is formed into platoons of vehicles, the lead vehicles of which are governed by wayside-mounted controllers. Excluding platoon leaders, vehicles are controlled by on-board controllers, termed car-following or following-law controllers, which continuously regulate vehicle spacing and velocity with respect to the preceding vehicle, and velocity with respect to an external, desired velocity. Wayside controllers, which communicate with vehicles only when they cross discrete control points along the guideway, provide “modified block control” of lead vehicles, maintaining a safe stopping distance such that collisions under an instantaneous stop cannot occur between vehicles of separate platoons. The proposed control appears suitable for realistic guideway conditions and provides flexibility in performance tradeoffs among wayside hardware, safety, nominal guideway line speed, and guideway vehicle capacity. Spaces generated between platoons under normal operation afford capability for merging from off-line queues.
Performance and Stability Characteristics of an Electrodynamically Levitated Vehicle Over a Split Guideway
Authors: Wong J. Y. , Howell J. P. , Rhodes R. G. , Mulhall B. E.
Published: July 2010

The results of an investigation into the performance and stability characteristics of an electrodynamically levitated vehicle using an integrated magnet system over a flat split guideway are described. The effects of system parameters on the lift/drag ratio, guidance and directional stability are examined in detail.
Dynamics of Flexible Cables Under Combined Vortex and Parametric Excitation
Authors: Trogdon S. A. , Wilson J. F. , Munson B. R.
Published: July 2010

The response of a flexible cable under the combined effects of transverse fluid loading (vortex shedding) and parametric excitation (time varying tension) is considered. The theoretical transient responses are obtained from the solution of sets of uncoupled Mathieu equations. Experimental results are presented for steady-state cases. The cable responses are characterized by a complex coupling between the two modes of excitation. It is hypothesized that this coupling can be best understood by obtaining experimental measures of a new constant K˜, related to the amplitude of vortex shedding loads.
Identification of Papermaking Process From Closed Loop Data by Bivariate Time Series Analysis
Authors: Phadke M. S. , Wu S. M.
Published: July 2010

The data used by Tee and Wu [5] for identification of the transfer function and the noise of a Fourdrinier paper machine are reanalyzed taking into account the feedback of the skilled operator. The identification procedure consists of fitting a bivariate time series to the input and output observations. The transfer function and the noise of the paper machine as well as those of the skilled operator are obtained by simple manipulations of the fitted bivariate model. The resulting model is physically interpreted and an attempt is made to locate the primary source of disturbance.
A Preliminary Analysis of Ski Release Binding Dynamic Properties
Authors: Mote C. D. , Hull M. L.
Published: July 2010

A piecewise, linear, two degree of freedom, ski release binding dynamic system model is presented for an elementary analysis of binding performance. Dynamic performance criteria and techniques for quantitative evaluation of ski release binding properties are discussed. Desirable binding properties along the loading path, where the ski and boot are separating, and desirable binding properties along the return path where the boot is returning to the ski centerline are discussed separately. General characteristics of the loading and return paths have practical application for binding function.
A Nonlinear Dynamic Model of a Once-Through Subcritical Steam Generator
Authors: Ray A. , Bowman H. F.
Published: July 2010

A dynamic thermal-hydraulic model of a once-through subcritical steam generator is presented which allows the investigation of power plant system transients. The three-section (economizer, evaporator, and superheater) model with time-varying phase boundaries is described by a set of nonlinear differential and algebraic equations derived from the fundamental equations of conservation of mass, momentum, and energy. The transient response of 8 process variables, due to 5 percent independent step disturbances in 5 input variables at 100 percent load, is discussed.
Closed Loop Control of Spark Advance Using a Cylinder Pressure Sensor
Authors: Hubbard M. , Dobson P. D. , Powell J. D.
Published: July 2010

The objective of the spark advance control technique discussed in this paper is to provide a schedule which is optimum in the presence of changing engine and environmental conditions. The paper shows the benefits of adaptable spark control, describes the ability of a cylinder pressure based system to adapt to optimum spark on a single cylinder laboratory engine and describes the transient performance of a controller mechanized in the laboratory. Averaged over the entire engine speed-load operating regime, the closed loop system yields average brake horsepower within 0.1 percent of optimum based solely on the cylinder pressure information. The system has demonstrated a transient settling time of 0.1 second.
A generic geometric calibration method for tomographic imaging systems with flat‐panel detectors—A detailed implementation guide
Authors: Li Xinhua , Zhang Da , Liu Bob
Published: July 2010

Purpose

To present a generic geometric calibration method for tomographic imaging systems with flat‐panel detectors in a very detailed manner, in the aim to provide a useful tool to the public domain.

Methods

The method is based on a projection matrix which represents a mapping from 3D object coordinate system to 2D projection image plane. The projection matrix can be determined experimentally through the imaging of a phantom of known marker geometry. Accurate implementation was accomplished through direct computation algorithms, including a novel ellipse fitting using singular value decomposition and data normalization. Benefits of the method include: (1) It is capable of being applied to systems of different scan trajectories, source‐detector alignments, and detector orientations; (2) projection matrices can be utilized in image reconstructions or in the extraction of explicit geometrical parameters; and (3) the method imposes minimal limits on the design of calibration phantom. C++ programs that calculate projection matrices and extract geometric parameters from them are also provided. For validation, the calibration method was applied to the computer simulation of a cone‐beam CT system, as well as to three tomosynthesis prototypes of different source‐detector movement patterns: Source and detector rotating synchronizedly; source rotating and detector wobbling; and source rotating and detector staying stationary.

Results

Projection matrices were computed on a view by view basis. Geometric parameters extracted from projection matrices were consistent with actual settings. Images were reconstructed by directly using projection matrices, and were compared to virtual Shepp–Logan image for CT simulation and to central projection images of CIRS breast phantoms for tomosynthesis prototypes. They showed no obvious distortion or blurring, indicating the high quality of geometric calibration results. When the computed central ray offsets were perturbed with Gaussian noises of 1 pixel standard deviation, the reconstructed image showed apparent distortion, which further demonstrated the accuracy of the geometric calibration method.

Conclusions

The method is suitable for tomographic imaging systems with flat‐panel detectors.
The energy dependence of lithium formate and alanine EPR dosimeters for medium energy x rays
Authors: Waldeland Einar , Hole Eli Olaug , Sagstuen Einar , Malinen Eirik
Published: July 2010

Purpose

To perform a systematic investigation of the energy dependence of alanine and lilthium formate EPR dosimeters for medium energy x rays.

Methods

Lithium formate and alanine EPR dosimeters were exposed to eight different x‐ray beam qualities, with nominal potentials ranging from 50 to 200 kV. Following ionometry based on standards of absorbed dose to water, the dosimeters were given two different doses of approximately 3 and 6 Gy for each radiation quality, with three dosimeters for each dose. A reference series was also irradiated to three different dose levels at a unit. The dose to water energy response, that is, the dosimeter reading per absorbed dose to water relative to that for ‐rays, was estimated for each beam quality. In addition, the energy response was calculated by Monte Carlo simulations and compared to the experimental energy response.

Results

The experimental energy response estimates ranged from 0.89 to 0.94 and from 0.68 to 0.90 for lithium formate and alanine, respectively. The uncertainties in the experimental energy response estimates were typically 3%. The relative effectiveness, that is, the ratio of the experimental energy response to that following Monte Carlo simulations was, on average, 0.96 and 0.94 for lithium formate and alanine, respectively.

Conclusions

This work shows that lithium formate dosimeters are less dependent on x‐ray energy than alanine. Furthermore, as the relative effectiveness for both lithium formate and alanine were systematically less than unity, the yield of radiation‐induced radicals is decreased following x‐irradiation compared to irradiation with ‐rays.
Fast‐marching segmentation of three‐dimensional intravascular ultrasound images: A pre‐ and post‐intervention study
Authors: Cardinal Marie‐Hélène Roy , Soulez Gilles , Tardif Jean‐Claude , Meunier Jean , Cloutier Guy
Published: July 2010

Purpose: Intravascular ultrasound (IVUS) is a vascular imaging technique that is used to study atherosclerosis since it has the ability to show the lumen and the vessel wall. Cross‐sectional images of blood vessels are produced and they provide quantitative assessment of the vascular wall, information about the nature of atherosclerotic lesions, as well as the plaque shape and size. Due to the ultrasound speckle, catheter artifacts, or calcification shadows, the automated analysis of large IVUS data sets represents an important challenge.

Methods: A multiple interface 3D fast‐marching method is presented for the detection of the lumen and external vessel wall boundaries. The segmentation is based on a combination of region and contour information, namely, the gray level probability density functions of the vessel structures and the intensity gradient. The detection of the lumen boundary is fully automatic. The segmentation method includes an interactive initialization procedure of the external vessel wall border. The segmentation method was applied to 20 in vivo IVUS data sets acquired from femoral arteries. This database contained three subgroups: Pullbacks acquired before balloon angioplasty , after the intervention , and at a 1 yr follow‐up examination . Results were compared to validation contours that were manually traced by two experts on more than 1500 individual frames.

Results: For all subgroups, no significant difference was found between the area measurements of the segmentation and validation contours for the lumen and external vessel wall. Moreover, high intraclass correlation coefficients between the area of the manually traced contours and detected boundaries with the fast‐marching method were obtained for both vessel layers over the whole database. The segmentation performance was also evaluated with point‐to‐point contour distances between segmentation results and manually traced contours. A good overall accuracy was obtained with average distances and maximum distances , indicating a good performance in regions lacking information or containing artifacts. Only small differences of less than a pixel (0.02 mm) were observed between the average distance metrics of each subgroup, which prove the segmentation consistency.

Conclusions: This new IVUS segmentation method provides accurate results that correspond well to the experts’ manually traced contours, but requires much less manual interactions and is faster.
Evaluation of two‐dimensional bolus effect of immobilization/support devices on skin doses: A radiochromic EBT film dosimetry study in phantom
Authors: Chiu‐Tsao Sou‐Tung , Chan Maria F.
Published: July 2010

Purpose

In this study, the authors have quantified the two‐dimensional (2D) perspective of skin dose increase using EBT film dosimetry in phantom in the presence of patient immobilization devices during conventional and IMRT treatments.

Methods

For 6 MV conventional photon field, the authors evaluated and quantified the 2D bolus effect on skin doses for six different common patient immobilization/support devices, including carbon fiber grid with Mylar sheet, Orfit carbon fiber base plate, balsa wood board, Styrofoam, perforated AquaPlast™ sheet, and alpha‐cradle. For 6 and 15 MV IMRT fields, a stack of two film layers positioned above a solid phantom was exposed at the air interface or in the presence of a patient alpha‐cradle. All the films were scanned and the pixel values were converted to doses based on an established calibration curve. The authors determined the 2D skin dose distributions, isodose curves, and cross‐sectional profiles at the surface layers with or without the immobilization/support device. The authors also generated and compared the dose area histograms (DAHs) and dose area products from the 2D skin dose distributions.

Results

In contrast with 20% relative dose [(RD) dose relative to on central axis] at 0.0153 cm in the film layer for 6 MV open field, the average RDs at the same depth in the film layer were 71%, 69%, 55%, and 57% for Orfit, balsa wood, Styrofoam, and alpha‐cradle, respectively. At the same depth, the RDs were 54% under a strut and 26% between neighboring struts of a carbon fiber grid with Mylar sheet, and between 34% and 56% for stretched perforated AquaPlast™ sheet. In the presence of the alpha‐cradle for the 6 MV (15 MV) IMRT fields, the hot spot doses at the effective measurement depths of 0.0153 and 0.0459 cm were 140% and 150% (83% and 89%), respectively, of the isocenter dose. The enhancement factor was defined as the ratio of a given DAH parameter (minimum dose received in a given area) with and without the support device. For 6 MV conventional field, the enhancement factor was the highest (3.4) for the Orfit carbon fiber plate. As for the IMRT field, the enhancement factors varied with the size of the area of interest and were as high as 3.8 (4.3) at the hot spot of area in the top film layer (0.0153 cm) for 6 MV (15 MV) beams.

Conclusions

Significant 2D bolus effect on skin dose in the presence of patient support and immobilization devices was confirmed and quantified with EBT film dosimetry. Furthermore, the EBT film has potential application forin vivo monitoring of the 2D skin dose distributions during patient treatments.
Wide field array calibration dependence on the stability of measured dose distributions
Authors: Simon Thomas A. , Simon William E. , Kahler Darren , Li Jonathan , Liu Chihray
Published: July 2010

Purpose

The aim of this work was to simulate the effect of dose distribution changes on detector array calibrations and to explore compensatory methods that are used during calibration measurements.

Methods

The array calibration technique that was investigated is known as wide field (WF) calibration. Using this method, a linear array [‐axis (65 detectors) of the IC PROFILER™ (Sun Nuclear Corporation, Melbourne, FL)] is calibrated with three measurements (, , and ); each measurement uses the same radiation field, which is larger than the array. For measurement configuration , the array is rotated by 180° from its position in ; for , the array is shifted by one detector from its position in . The relative detector sensitivities are then determined through ratios of detector readings at the same field locations (using and ). This method results in error propagation that is proportional to the number of detectors in the array. During the procedure, the calibration protocol operates under three postulates, which state that (a) the beam shape does not change between measurements; (b) the relative sensitivities of the detectors do not change; and (c) the scatter to the array does not change as the array is moved. The WF calibration's sensitivity to a postulate (a) violation was quantified by applying a sine shaped perturbation (of up to 0.1%) to , , or , and then determining the change relative to a baseline calibration. Postulate (a) violations were minimized by using a continuous beam and mechanized array movement during and . A continuously on beam demonstrated more stable beam symmetry as compared to cycling the beam on and off between measurements. Additional side‐scatter was also used to satisfy postulate (c).

Results

Simulated symmetry perturbations of 0.1% to or resulted in calibration errors of up to 2%; was relatively immune to perturbation ( error). Wide field calibration error on a linear accelerator with similar symmetry variations was ±1.6%. Using a continuous beam during and with additional side‐scatter reduced the calibration error from ±1.6% to ±0.48%.

Conclusions

This work increased the reproducibility of WF calibrations by limiting the effect of measurement perturbations primarily due to linear accelerator symmetry variations. The same technique would work for any array using WF calibration.
Total skin electron therapy (TSET): A reimplementation using radiochromic films and IAEA TRS‐398 code of practice
Authors: Schiapparelli P. , Zefiro D. , Massone F. , Taccini G.
Published: July 2010

Purpose

The aim of this work is to present an updated implementation of total skin electron therapy (TSET) using IAEA TRS‐398 code of practice for absolute dosimetry and taking advantage of the use of radiochromic films. The optimization of quality control tests is also included.

Methods

A Varian 2100 C/D linear accelerator equipped with the special procedure (high dose rate total skin electron mode, ) was employed to perform TSET irradiations using the modified Stanford technique. The commissioning was performed following the AAPM report 23 recommendations. In particular, for dual‐field beams irradiation, the optimal tilt angle was investigated and the dose distribution in the treatment plane was measured. For a complete six dual‐field beams irradiation, the treatment skin dose on the surface of a cylindrical phantom was evaluated by radiochromic films and the factor which relates the single dual‐field skin dose to the six dual‐field skin dose was assessed. Since the TRS‐398 reference conditions do not meet the requirements of TSET absolute dosimetry, GafChromic EBT films were also employed to check and validate the application of the protocol. Simplified procedures were studied to verify beam constancy in PMMA phantoms without the more difficult setup of total skin irradiation.

Results

The optimized geometrical setup for dual‐field beams was: Tilt , , and the beam degrader placed at 320 cm from the source. As regards to dose homogeneity in the treatment plane, for dual‐field beams irradiation, the mean relative dose value was (normalizing to 100% at the calibration point level). For six dual‐field beams irradiation, the multiplication factor was 2.63. In addition, beam quality, dose rate, and bremsstrahlung contribution were also suitable for TSET treatments. The TRS‐398 code of practice was used for TSET dosimetry, as dose measurements performed by ionization chamber and radiochromic film agreed within 2.5%. Simplified quality control tests and baseline values were presented in order to check flatness, symmetry, and field size with radiochromic films and output and beam quality constancy with ionization chamber. Short‐term reproducibility and MU linearity tests were also included.

Conclusions

Commissioning parameters met the requirements of TSET treatments and the matching of AAPM guidelines with the IAEA code of practice was successful. Frequent beam performance controls can be easily performed through the presented quality assurance tests. Radiochromic dosimetry facilitated the TSET commissioning and played a major role to validate the application of TRS‐398.
A symmetric nonrigid registration method to handle large organ deformations in cervical cancer patients
Authors: Bondar Luiza , Hoogeman Mischa S. , Vásquez Osorio Eliana M. , Heijmen Ben J. M.
Published: July 2010

Purpose

Modern radiotherapy requires assessment of patient anatomical changes. By using unidirectional registration methods, the quantified anatomical changes are asymmetric, i.e., depend on the direction of the registration. Moreover, the registration is challenged by the large and complex organ deformations that can occur in, e.g., cervical cancer patients. The aim of this work was to develop, test, and validate a symmetric feature‐based nonrigid registration method that can handle organs with large‐scale deformations.

Methods

A symmetric version of the unidirectional thin plate spline robust point matching (TPS‐RPM) algorithm was developed, implemented, tested, and validated. Tests were performed by using the delineated cervix and uterus and bladder in CT scans of five cervical cancer patients. For each patient, five CT scans with a large variability in organ shape, volume, and deformations were acquired. Both the symmetric and the unidirectional algorithm were employed to calculate the registration geometric accuracy (surface distance and surface coverage errors), the inverse consistency, the residual distances after transforming anatomical landmarks, and the registration time. Additionally, to facilitate the further use of our symmetric method, a large set of input parameters was tested.

Results

The developed symmetric algorithm handled successfully the registration of bladders with extreme volume change for which TPS‐RPM failed. Compared to the unidirectional algorithm the symmetric algorithm improved, for the registration of organs with large volume change, the inverse consistency by 78% and the surface coverage by 46%. Similarly, for organs with small volume change, the symmetric algorithm improved the inverse consistency by 69% and the surface coverage by 13%. The method allowed for anatomically coherent registration in only 35 s for cervix‐uterus and 151 s for bladder, while keeping the inverse consistency errors around 1 mm and the surface matching errors below 1 mm. Compared to rigid alignment the symmetric method reduced the residual distances between anatomical landmarks from a range of to a range of .

Conclusions

The developed symmetric method could be employed to perform fast, accurate, consistent, and anatomically coherent registration of organs with large and complex deformations. Therefore, the method is a useful tool that could support further developments in high precision image guided radiotherapy.
Contrast detection in fluid‐saturated media with magnetic resonance poroelastography
Authors: Perriñez Phillip R. , Pattison Adam J. , Kennedy Francis E. , Weaver John B. , Paulsen Keith D.
Published: July 2010

Purpose

Recent interest in the poroelastic behavior of tissues has led to the development of magnetic resonance poroelastography (MRPE) as an alternative to single‐phase MR elastographic image reconstruction. In addition to the elastic parameters (i.e., Lamé's constants) commonly associated with magnetic resonance elastography (MRE), MRPE enables estimation of the time‐harmonic pore‐pressure field induced by external mechanical vibration.

Methods

This study presents numerical simulations that demonstrate the sensitivity of the computed displacement and pore‐pressure fields toa priori estimates of the experimentally derived model parameters. In addition, experimental data collected in three poroelastic phantoms are used to assess the quantitative accuracy of MR poroelastographic imaging through comparisons with both quasistatic and dynamic mechanical tests.

Results

The results indicate hydraulic conductivity to be the dominant parameter influencing the deformation behavior of poroelastic media under conditions applied during MRE. MRPE estimation of the matrix shear modulus was bracketed by the values determined from independent quasistatic and dynamic mechanical measurements as expected, whereas the contrast ratios for embedded inclusions were quantitatively similar (10%–15% difference between the reconstructed images and the mechanical tests).

Conclusions

The findings suggest that the addition of hydraulic conductivity and a viscoelastic solid component as parameters in the reconstruction may be warranted.
Automatic image guidance for prostate IMRT using low dose CBCT
Authors: Wierzbicki Marcin , Schaly Bryan , Peters Terry , Barnett Rob
Published: July 2010

Purpose

Varian's On‐Board Imager is a linac‐integrated cone‐beam CT (CBCT) system used at the authors’ institution to acquire images prior to delivering each fraction of prostate intensity modulated radiotherapy. The images are used to determine a couch shift that realigns the tumor with the position obtained in the planning CT. However, this manual image‐guided radiotherapy (IGRT) technique is operator dependent, time consuming, offers limited degrees of freedom, and requires significant imaging dose over the course of treatment. To overcome these problems, the authors propose two fully automatic IGRT techniques that require significantly less imaging dose.

Methods

Dose is reduced by lowering the x‐ray tube mA s during CBCT acquisition at the cost of increasing image noise. In “forward” IGRT, the CBCT image is automatically registered to the planning CT to obtain the necessary couch shift. The “reverse” technique offers additional degrees of freedom as it involves nonrigid registration of the planning CT to the CBCT. Both techniques were evaluated using images of an anthropomorphic phantom with simulated motion and by retrospectively analyzing data from ten prostate cancer patients.

Results

IGRT error for the phantom data at 100% relative imaging dose was , , and for setup only, forward, and reverse techniques, respectively. For patient images acquired at 100% relative imaging dose, the errors were , , , and for setup only, manual forward (performed clinically), automatic forward, and reverse IGRT, respectively. Furthermore, imaging dose could be reduced to 20% without a significant loss in image guidance accuracy.

Conclusions

The presented image guidance methods are accurate while requiring only 20% of the standard imaging dose. The combination of low dose, automation, and accuracy enables frequent corrections during treatment, possibly leading to reduced margins and improved treatment outcomes.
Multibeam field emission x‐ray system with half‐scan reconstruction algorithm
Authors: Lu Yang , Yu Hengyong , Cao Guohua , Zhao Jun , Wang Ge , Zhou Otto
Published: July 2010

Purpose

In this article, the authors propose a multibeam field emission x‐ray (MBFEX) system along with a half‐scan fan‐beam reconstruction algorithm.

Methods

The proposed system consists of a linear CNT‐based MBFEX source array, a single large area detector that is divided into same number of segments as the number of x‐ray beams, a multihole collimator that aligns each beam with a corresponding detector segment, and a sample rotation stage. The collimator is placed between the source and the object to restrict the x‐ray radiations through the target object only. In this design, all the x‐ray beams are activated simultaneously to provide multiple projection views of the object. The detector is virtually segmented and synchronized with the x‐ray exposure and the physiological signals when gating is involved. The transmitted x‐ray intensity from each beam is collected by the corresponding segment on the detector. After each exposure, the object is rotated by a step angle until sufficient data set is collected. The half‐scan reconstruction formula for MBFEX system is derived from the conventional filtered backprojection algorithm. To demonstrate the advantages of the system and method in reducing motion artifacts, the authors performed simulations with both standard and dynamic Shepp–Logan phantoms.

Results

The numerical results indicate that the proposed multibeam system and the associated half‐scan algorithm can effectively reduce the scanning time and improve the image quality for a time‐varying object.

Conclusions

The MBFEX technique offers an opportunity for the innovation of multisource imaging system.
Efficient generation of a magnetic field‐free line
Authors: Knopp Tobias , Erbe Marlitt , Biederer Sven , Sattel Timo F. , Buzug Thorsten M.
Published: July 2010

Purpose

Signal encoding in magnetic particle imaging (MPI) is achieved by moving a field‐free point (FFP) through the region of interest. One way to increase the sensitivity of the method is to scan the region of interest with a field‐free line (FFL) instead of the FFP. Recently, the first feasible FFL coil setup was introduced. The purpose of this article is to improve the efficiency of the FFL coil geometry even further.

Methods

In order to reduce the electrical power loss of the setup, an additional Maxwell coil pair is introduced that is tailored to generate the static part of the FFL field.

Results

Using the proposed coil assembly, the electrical power loss for the generation of a rotating FFL is considerably reduced compared to previously known coil setups. Furthermore, the quality of the generated FFL is significantly increased.

Conclusions

The proposed coil assembly is almost as efficient as an equivalent FFP scanner. Furthermore, the assembly cannot only be used for FFL imaging but for FFP imaging as well. Hence, the findings of this article denote an important step toward the first practical implementation of the FFL coil geometry.
Light emission efficiency and imaging performance of powder scintillator under x‐ray radiography conditions
Authors: Michail C. M. , Fountos G. P. , Liaparinos P. F. , Kalyvas N. E. , Valais I. , Kandarakis I. S. , Panayiotakis G. S.
Published: July 2010

Purpose

To evaluate powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography. is nonhygroscopic, emitting red light with decay time close to that of .

Methods

The light intensity emitted per unit of x‐ray exposure rate (absolute luminescence efficiency) was measured for laboratory prepared screens with coating thicknesses of 33.1, 46.4, 63.1, 78.3, and and tube voltages ranging from 50 to 140 kVp. Parameters related to image quality such as the modulation transfer function (MTF) and the detective quantum efficiency (DQE) were also experimentally examined. In addition, a previously validated Monte Carlo code was used to estimate intrinsic x‐ray absorption and optical properties, as well as the MTF and the Swank factor of the scintillators.

Results

light intensity was found higher than that of single CsI:Tl crystal for tube voltages up to 100 kVp. The MTF and the DQE were found to be comparable with those of and CsI:Tl screens. MTF estimated by the Monte Carlo code was found very close to the experimental MTF values. showed peak emission in the wavelength range 620–630 nm. Its emission spectrum was excellently matched to various optical detectors (photodiodes, photocathodes, CCDs, and CMOS) employed in flat panel detectors.

Conclusions

is an efficient phosphor potentially well suited to radiography and especially to some digital detectors sensitive to red light.
Dosimetric characterization of the iBEAM evo carbon fiber couch for radiotherapy
Authors: Smith David W. , Christophides Damianos , Dean Christopher , Naisbit Mitchell , Mason Joshua , Morgan Andrew
Published: July 2010

Purpose

This study characterizes the dosimetric properties of the iBEAM evo carbon fiber couch manufactured by Medical Intelligence and examines the accuracy of the CMS XiO and Nucletron Oncentra Masterplan (OMP) treatment planning systems for calculating beam attenuation due to the presence of the couch.

Methods

To assess the homogeneity of the couch, it was CT scanned at isocentric height and a number of signal intensity profiles were generated and analyzed. To simplify experimental procedures, surface dose and central axis depth dose measurements were performed in a solid water slab phantom using Gafchromic film for 6 and 10 MV photon beams at gantry angles of 0° (normal incidence), 30°, and 60° with an inverted iBEAM couch placed on top of the phantom. Attenuation measurements were performed in a cylindrical solid water phantom with an ionization chamber positioned at the isocenter. Measurements were taken for gantry angles from 0° to 90° in 10° increments for both 6 and 10 MV photon beams. This setup was replicated in the XiO and OMP treatment planning systems. Dose was calculated using the pencil beam, collapsed cone, convolution, and superposition algorithms.

Results

The CT scan of the couch showed that it was uniformly constructed. Surface dose increased by for a 6 MV beam and for a 10 MV beam passing through the couch at normal incidence. Obliquely incident beams resulted in a higher surface dose compared to normally incident beams for both open fields and fields with the couch present. Depth dose curves showed that the presence of the couch resulted in an increase in dose in the build up region. For 6 and 10 MV beams incident at 60°, nearly all skin sparing was lost. Attenuation measurements derived using the ionization chamber varied from 2.7% (0°) to a maximum of 4.6% (50°) for a 6 MV beam and from 1.9% (0°) to a maximum of 4.0% (50°) for a 10 MV beam. The pencil beam and convolution algorithms failed to accurately calculate couch attenuation. The collapsed cone and superposition algorithms calculated attenuation within an absolute error of ±1.2% for 6 MV and ±0.8% for 10 MV for gantry angles from 0° to 40°. Some differences in attenuation were observed dependent on how the couch was contoured.

Conclusions

These results demonstrate that the presence of the iBEAM evo carbon fiber couch increases the surface dose and dose in the build up region. The inclusion of the couch in the planning scan is limited by the field of view employed and the couch height at the time of CT scanning.
Evaluating Auger electrons for targeted tumor radiotherapy by computational methods
Authors: Tavares Adriana Alexandre S. , Tavares João Manuel R. S.
Published: July 2010

Purpose

Technetium‐99m has been widely used as an imaging agent but only recently has been considered for therapeutic applications. This study aims to analyze the potential use of Auger electrons for targeted tumor radiotherapy by evaluating the DNA damage and its probability of correct repair and by studying the cellular kinetics, following Auger electron irradiation in comparison to iodine‐131 beta minus particles and astatine‐211 alpha particle irradiation.

Methods

Computational models were used to estimate the yield of DNA damage (fast Monte Carlo damage algorithm), the probability of correct repair (Monte Carlo excision repair algorithm), and cell kinetic effects (virtual cell radiobiology algorithm) after irradiation with the selected particles.

Results

The results obtained with the algorithms used suggested that CKMMX (all M‐shell Coster–Kroning—CK—and super‐CK transitions) electrons and Auger MXY (all M‐shell Auger transitions) have a therapeutic potential comparable to high linear energy transfer alpha particles and higher than beta minus particles. All the other electrons had a therapeutic potential similar to beta minus particles.

Conclusions

CKMMX electrons and Auger MXY presented a higher probability to induce apoptosis than beta minus particles and a probability similar to alpha particles. Based on the results here, CKMMX electrons and Auger MXY are useful electrons for targeted tumor radiotherapy.
The sensitivity of patient specific IMRT QC to systematic MLC leaf bank offset errors
Authors: Rangel Alejandra , Palte Gesa , Dunscombe Peter
Published: July 2010

Purpose

Patient specific IMRT QC is performed routinely in many clinics as a safeguard against errors and inaccuracies which may be introduced during the complex planning, data transfer, and delivery phases of this type of treatment. The purpose of this work is to evaluate the feasibility of detecting systematic errors in MLC leaf bank position with patient specific checks.

Methods

9 head and neck (H&N) and 14 prostate IMRT beams were delivered using MLC files containing systematic offsets (±1 mm in two banks, ±0.5 mm in two banks, and 1 mm in one bank of leaves). The beams were measured using bothMAPCHECK™ (Sun Nuclear Corp., Melbourne, FL) and the aS1000 electronic portal imaging device (Varian Medical Systems, Palo Alto, CA). Comparisons with calculated fields, without offsets, were made using commonly adopted criteria including absolute dose (AD) difference, relative dose difference, distance to agreement (DTA), and the gamma index.

Results

The criteria most sensitive to systematic leaf bank offsets were the 3% AD, 3 mm DTA forMAPCHECK™ and the gamma index with 2% AD and 2 mm DTA for the EPID. The criterion based on the relative dose measurements was the least sensitive to MLC offsets. More highly modulated fields, i.e., H&N, showed greater changes in the percentage of passing points due to systematic MLC inaccuracy than prostate fields.

Conclusions

None of the techniques or criteria tested is sufficiently sensitive, with the population of IMRT fields, to detect a systematic MLC offset at a clinically significant level on an individual field. Patient specific QC cannot, therefore, substitute for routine QC of the MLC itself.
Impact of source‐production revision on the dose‐rate constant of interstitial brachytherapy sources
Authors: Chen Zhe (Jay) , Bongiorni Paul , Nath Ravinder
Published: July 2010

Purpose

Since its introduction in 2004, the model CS‐1 Rev.1 source has been used in many radiation therapy clinics for prostate brachytherapy. In 2006, this source model underwent a Rev.2 production revision. The aim of this work was to investigate the dosimetric influences of the Rev.2 production revision using high‐resolution photon spectrometry.

Methods

Three CS‐1 Rev.1 and three CS‐1 Rev.2 sources were used in this study. The relative photon energy spectrum emitted by each source in the transverse bisector of the source was measured using a high‐resolution germanium detector designed for low‐energy photon spectrometry. Based on the measured photon energy spectrum and the radioactivity distribution in the source, the dose‐rate constant of each source was determined. The effects of the Rev.2 production revision were quantified by comparing the emitted photon energy spectra and the values determined for the sources manufactured before and after the production revision.

Results

The relative photon energy spectrum originating from the principal emissions of was found to be nearly identical before and after the Rev.2 revision. However, the portion of the spectrum originating from the production of fluorescent x rays in niobium, a trace element present in the source construction materials, was found to differ significantly between the Rev.1 and Rev.2 sources. The peak intensity of the and fluorescent x rays from the Rev.2 source was approximately 35% of that from the Rev.1 source. Consequently, the nominal value of the Rev.2 source was found to be greater than that determined for the Rev.1 source by approximately .

Conclusions

A significant reduction (65%) in relative niobium fluorescent x‐ray yield was observed in the Rev.2 sources. The impact of this reduction on the dose‐rate constant was found to be small, with a relative difference of less than 1%. This study demonstrates that photon spectrometry can be used as a sensitive and convenient tool for monitoring and for quantifying the dosimetric effects of brachytherapy source‐production revisions. Because production revision can change both the geometry and the atomic composition of brachytherapy sources, its dosimetric impact should be carefully monitored and evaluated for each production revision.
Computerized comprehensive data analysis of Lung Imaging Database Consortium (LIDC)
Authors: Tan Jun , Pu Jiantao , Zheng Bin , Wang Xingwei , Leader Joseph K.
Published: July 2010

Purpose

Lung Image Database Consortium (LIDC) is the largest public CT image database of lung nodules. In this study, the authors present a comprehensive and the most updated analysis of this dynamically growing database under the help of a computerized tool, aiming to assist researchers to optimally use this database for lung cancer related investigations.

Methods

The authors developed a computer scheme to automatically match the nodule outlines marked manually by radiologists on CT images. A large variety of characteristics regarding the annotated nodules in the database including volume, spiculation level, elongation, interobserver variability, as well as the intersection of delineated nodule voxels and overlapping ratio between the same nodules marked by different radiologists are automatically calculated and summarized. The scheme was applied to analyze all 157 examinations with complete annotation data currently available in LIDC dataset.

Results

The scheme summarizes the statistical distributions of the abovementioned geometric and diagnosis features. Among the 391 nodules, (1) 365 (93.35%) have principal axis length ; (2) 120, 75, 76, and 120 were marked by one, two, three, and four radiologists, respectively; and (3) 122 (32.48%) have the maximum volume overlapping ratios for the delineations of two radiologists, while 198 (50.64%) have the maximum volume overlapping ratios . The results also showed that 72.89% of the nodules were assessed with malignancy score between 2 and 4, and only 7.93% of these nodules were considered as severely malignant (malignancy ).

Conclusions

This study demonstrates that LIDC contains examinations covering a diverse distribution of nodule characteristics and it can be a useful resource to assess the performance of the nodule detection and/or segmentation schemes.
Evaluation of EBT‐2 model GAFCHROMIC™ film performance in water
Authors: Aldelaijan Saad , Devic Slobodan , Mohammed Huriyyah , Tomic Nada , Liang Li‐Heng , DeBlois Francois , Seuntjens Jan
Published: July 2010

Purpose

The authors present results of the measurements on the impact of radiochromic film immersion in water. The impact of film piece size, initial optical density, postimmersion waiting time prior to scanning, and the time film was kept in water has been investigated. The authors also investigated the pathways of water penetration into the film during the film immersion in water.

Methods

To study the impact of water immersion on change in optical density, the authors used various sizes of the latest EBT‐2 model GAFCHROMIC™ film: , , and . In addition, to test any existing dependence of the film's optical density on water diffusion, the authors used two sets of films: Unexposed (0 Gy) and film pieces exposed to a dose of 3 Gy. Times that film pieces were left in water ranged from 30 min to 24 h, and once the film was permanently removed from water, the authors also studied the impact of the scanning time that ranged from 0 (films scanned right after removal from water) to 72 h postimmersion.

Results

While the penetration depth can reach as much as 9 mm around the edges of the EBT‐2 GAFCHROMIC™ film, the anticipated dose error due to the change in optical density due to the water immersion appears to be negligible for the short immersions of the order of 30 min. However, as the immersion time increases, the anticipated dose error may reach 22 cGy on a piece of film, which corresponds to 7% dose error at 3 Gy of measured dose.

Conclusions

In this work, the authors report on an undoubted impact of radiochromic film immersion in water on the measured change in optical density, which may lead to systematic errors in dose measurements if the film is kept in water for longer periods of time. The magnitude of the impact depends on many parameters: Size of the film piece, initial optical density, postimmersion waiting time prior to scanning (defined by the current radiochromic film dosimetry protocol in place), and the time film was kept in water. The authors also suggested various approaches in correcting for the change in netOD due to water penetration into the film, but the authors believe that the use of the control film piece would be the most appropriate.
Quantitative microwave‐induced thermoacoustic tomography
Authors: Yao Lei , Guo Gaofeng , Jiang Huabei
Published: July 2010

Purpose

Microwave‐induced thermoacoustic tomography (MI‐TAT) is an imaging modality that exploits dielectric contrast while producing images with high ultrasound resolution. Existing reconstruction algorithms for MI‐TAT are qualitative and can image only the distribution of the absorbed microwave energy or power loss density. Here the authors describe a method for quantitative MI‐TAT and obtain the distribution of dielectric property which directly correlates with tissue structural and functional information.

Methods

The authors implement the quantitative MI‐TAT method based on the finite‐element (FE) solution to the Helmholtz equation for electromagnetic field coupled with the thermoacoustic wave equation. Regularization techniques are also used in the FE‐based reconstruction algorithm.

Results

Simulation results are obtained under various practical scenarios including different noise levels, different contrast levels between the heterogeneity and background region, and multiple targets with various sizes and shapes.

Conclusions

The quantitative MI‐TAT method described can provide accurate recovery of conductivity distribution in heterogeneous media and is insensitive to noise effect.
Regulation of Notch1 Signaling by Nrf2: Implications for Tissue Regeneration
Authors: Wakabayashi Nobunao , Shin Soona , Slocum Stephen L. , Agoston Elin S. , Wakabayashi Junko , Kwak Mi-Kyoung , Misra Vikas , Biswal Shyam , Yamamoto Masayuki , Kensler Thomas W.
Published: July 2010

The cell survival pathway mediated by the transcription factor Nrf2 facilitates tissue regeneration by promoting Notch1 signaling.
Signaling to Transcription Networks in the Neuronal Retrograde Injury Response
Authors: Michaelevski Izhak , Segal-Ruder Yael , Rozenbaum Meir , Medzihradszky Katalin F. , Shalem Ophir , Coppola Giovanni , Horn-Saban Shirley , Ben-Yaakov Keren , Dagan Shachar Y. , Rishal Ida , Geschwind Daniel H. , Pilpel Yitzhak , Burlingame Alma L. , Fainzilber Mike
Published: July 2010

Robustness in nerve injury responses results from control of axon-to-soma signaling networks by multiple regulatory components.
Radical Autonomic Insufficiency
Authors: Gough Nancy R.
Published: July 2010

Diabetic sympathetic dysfunction may result from an adaptive response to excess circulating glucose.