bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial distribution and temporal dynamics of high‐elevation forest stands in southern Siberia
Authors: Kharuk Vyacheslav I. , Ranson Kenneth J. , Im Sergey T. , Vdovin Alexander S.
Published: June 2010

Aim  To evaluate the hypothesis that topographic features of high‐elevation mountain environments govern spatial distribution and climate‐driven dynamics of the forest.

Location  Upper mountain forest stands (elevation range 1800–2600 m) in the mountains of southern Siberia.

Methods  Archive maps, satellite and on‐ground data from1960 to 2002 were used. Data were normalized to avoid bias caused by uneven distribution of topographic features (elevation, azimuth and slope steepness) within the analysed area. Spatial distribution of forest stands was analysed with respect to topography based on a digital elevation model (DEM).

Results  Spatial patterns in mountain forests are anisotropic with respect to azimuth, slope steepness and elevation. At a given elevation, the majority of forests occupied slopes with greater than mean slope values. As the elevation increased, forests shifted to steeper slopes. The orientation of forest azimuth distribution changed clockwise with increase in elevation (the total shift was 120°), indicating a combined effect of wind and water stress on the observed forest patterns. Warming caused changes in the forest distribution patterns during the last four decades. The area of closed forests increased 1.5 times, which was attributed to increased stand density and tree migration. The migration rate was 1.5 ± 0.9 m year–1, causing a mean forest line shift of 63 ± 37 m. Along with upward migration, downward tree migration onto hill slopes was observed. Changes in tree morphology were also noted as widespread transformation of the prostrate forms of Siberian pine and larch into erect forms.

Main conclusions  The spatial pattern of upper mountain forests as well as the response of forests to warming strongly depends on topographic relief features (elevation, azimuth and slope steepness). With elevation increase (and thus a harsher environment) forests shifted to steep wind‐protected slopes. A considerable increase in the stand area and increased elevation of the upper forest line was observed coincident with the climate warming that was observed. Warming promotes migration of trees to areas that are less protected from winter desiccation and snow abrasion (i.e. areas with lower values of slope steepness). Climate‐induced forest response has significantly modified the spatial patterns of high‐elevation forests in southern Siberia during the last four decades, as well as tree morphology.
In‐situ oxygen profiling and lignin modification in guts of wood‐feeding termites
Authors: Ke Jing , Sun Jian‐Zhong , Nguyen Hung D. , Singh Deepak , Lee Karmen C. , Beyenal Haluk , Chen Shu‐Lin
Published: June 2010

Abstract  Reports on the capability of wood‐feeding termites (WFTs) in degrading wood particles and on the existence of aerobic environment in the localized guts suggest that their high efficiency of cellulose utilization is not only caused by cellulase, but also by biochemical factors that pretreat lignin. We thus extend the hypothesis that for highly efficient accessibility of cellulose, there should be direct evidence of lignin modification before the hindgut. The lignin degradation/modification is facilitated by the oxygenated environment in intestinal microhabitats. To test our hypothesis, we conducted experiments using a dissolved oxygen microelectrode with a tip diameter < 10 μm to measure oxygen profiles in intestinal microhabitats of both Coptotermes formosanus (Shiraki) and Reticulitermes flavipes (Kollar). Lignin modification during passage through their three gut segments was also analyzed with pyrolysis gas chromatography/mass spectrometry. The data showed relatively high levels of oxygen in the midgut that could have promoted lignin oxidation. Consistent with the oxygen measurements, lignin modifications were also detected. In support of previously proposed hypotheses, these results demonstrate that lignin disruption, which pretreats wood for cellulose utilization, is initiated in the foregut, and continues in the midgut in both termites.
Molecular approaches to study the insect gut symbiotic microbiota at the ‘omics’ age
Authors: Shi Weibing , Syrenne Ryan , Sun Jian‐Zhong , Yuan Joshua S.
Published: June 2010

Abstract  Insect gut symbiotic microbiota play essential roles in the growth, development, pathogenesis and environmental adaptation of host insects. The molecular and systems level analysis of insect gut symbiotic microbial community will allow us to discover novel biocatalysts for biomass deconstruction and to develop innovative strategies for pest management. We hereby review the various molecular biology techniques as applied to insect gut symbiont analysis. This review aims to serve as an informative resource for experimental design and research strategy development in the field. We first discuss various strategies for sample preparation and their pros and cons. The traditional molecular techniques like DGGE, RFLP and FISH are covered with respect to how they are applied to study the composition, diversity and dynamics of insect gut symbiotic microbiota. We then focus on the various ‘omics’ techniques. The metagenome analysis together with the recent advancements in next‐generation sequencing will provide enormous sequencing information, allowing in‐depth microbial diversity analysis and modeling of pathways for biological processes such as biomass degradation. The metagenome sequencing will also enable the study of system dynamics and gene expression with metatranscriptome and metaproteome methods. The integration of different ‘omics’ level data will allow us to understand how insect gut works as a system to carry out its functions. The molecular and systems‐level understanding will also guide the reverse design of next‐generation biorefinery.
Mining diversity of the natural biorefinery housed within Tipula abdominalis larvae for use in an industrial biorefinery for production of lignocellulosic ethanol
Authors: Cook Dana M. , Doran‐Peterson Joy
Published: June 2010

Abstract  Although they are the largest taxonomic group of animals, relatively few insects have been examined for symbiotic relationships with micro‐organisms. However, this is rapidly changing because of the potential for examination of the natural insect–microbe–lignocellulose interactions to provide insights for biofuel technology. Micro‐organisms associated with lignocellulose‐consuming insects often facilitate the digestion of the recalcitrant plant diet; therefore these microbial communities may be mined for novel lignocellulose‐degrading microbes, or for robust and inexpensive biocatalysts necessary for economically feasible biofuel production from lignocellulose. These insect–microbe interactions are influenced by the ecosystem and specific lignocellulose diet, and appreciating the whole ecosystem–insect–microbiota–lignocellulose as a natural biorefinery provides a rich and diverse framework from which to design novel industrial processes. One such natural biorefinery, the Tipula abdominalis larvae in riparian ecosystems, is reviewed herein with applications for biochemical processes and overcoming challenges involved in conversion of lignocellulosic biomass to fuel ethanol. From the dense and diverse T. abdominalis larval hindgut microbial community, a cellulolytic bacterial isolate, 27C64, demonstrated enzymatic activity toward many model plant polymers and also produced a bacterial antibiotic. 27C64 was co‐cultured with yeast in fermentation of pine to ethanol, which allowed for a 20% reduction of commercial enzyme. In this study, a micro‐organism from a lignocellulose‐consuming insect was successfully applied for improvement of biomass‐to‐biofuel technology.
Analysis of cellulolytic and hemicellulolytic enzyme activity within the Tipula abdominalis (Diptera: Tipulidae) larval gut and characterization of Crocebacterium ilecola gen. nov., sp. nov., isolated from the Tipula abdominalis larval hindgut
Authors: Rogers Theresa E. , Doran‐Peterson Joy
Published: June 2010

Abstract  In forested stream ecosystems of the north and eastern United States, larvae of the aquatic crane fly Tipula abdominalis are important shredders of leaf litter detritus. T. abdominalis larvae harbor a dense and diverse microbial community in their hindgut that may aide in the degradation of lignocellulose. In this study, the activities of cellulolytic and hemicellulolytic enzymes were demonstrated from hindgut extracts and from bacterial isolates using model sugar substrates. One of the bacterial isolates was further characterized as a member of the family Microbacteriaceae. Taxonomic position of the isolate within this family was determined by a polyphasic approach, as is commonly employed for the separation of genera within the family Microbacteriaceae. The bacterial isolate is Gram‐type positive, motile, non‐sporulating, and rod‐shaped. The G + C content of the DNA is 64.9 mol%. The cell wall contains B2γ type peptidoglycan, D‐ and L‐diaminobutyric acid as the diamino acid, and rhamnose as the predominant sugar. The predominant fatty acids are 12‐methyltetradecanoic acid (ai‐C15:0) and 14‐methylhexadecanoic acid (ai‐C17:0). The isolate forms a distinct lineage within the family Microbacteriaceae, as determined by 16S rRNA sequence analysis. We propose the name Crocebacterium ilecola gen. nov., sp. nov., to accommodate this bacterial isolate. The type species is T202T (ATCC BAA‐1359; GenBank Accession DQ826511).
Up to D[eb]ate on Raising and Control Part 2: The Empirical Range of the Constructions and Research on their Acquisition
Authors: Kirby Susannah , Davies William D. , Dubinsky Stanley
Published: June 2010

This is the second part of a two‐part article that reviews a number of the current debates regarding raising and control constructions. The issues addressed in this part include the spectrum of related raising (e.g. possessor raising, further raising) and control (partial, split, generic, super‐equi) phenomena; cross‐linguistic typology, including backward and copy constructions; and their acquisition in child language.
Sociolinguistics and Perception
Authors: Campbell‐Kibler Kathryn
Published: June 2010

The social perception and evaluation of language are key elements in sociolinguistic phenomena. While perceptual studies have long played a role in the study of linguistic variation, they have not enjoyed central status, in contrast to their widespread use in the field of language attitudes. Recently, however, interest in the perceptual study of variation has grown. Three threads of research on sociolinguistic perception are discussed: the social and affective evaluation of language, the identification of social information from speech and the influence of social information on linguistic comprehension. Finally, methodological and theoretical developments within the field of variation are explored that place perceptual studies at the heart of the variationist enterprise.
Secular Sediment Waves, Channel Bed Waves, and Legacy Sediment
Authors: Allan James L.
Published: June 2010

The concept of sediment waves is reviewed and clarifications are proposed for nomenclature concerning vertical channel responses to large fluvial sediment fluxes over a period of a decade or longer. Gilbert’s (1917) original sediment waves are re‐evaluated at their type locale and used to develop a consistent set of definitions. A ‘sediment wave’ represents a transient sediment flux that includes but is not necessarily identical to a ‘channel bed wave’ that represents the rise and fall of the bed in response to sedimentation. A large‐scale sediment wave results when a major sediment‐delivery event generates an aggradation–degradation episode (ADE). It may leave a legacy of sediment deposited on valley bottoms. Gilbert’s classic sediment‐wave model was empirically based on changes in bed elevations but was described as a sediment flux. He described downstream translation of an attenuating symmetrical wave although it was too large and disjointed to have a coherent waveform. Rapid return of bed elevations to pre‐sedimentation levels in Gilbert’s wave should not be mistaken for exhaustion of sediment. The common concept of a symmetrical sediment wave representing the time series of sediment loads is not accurate for large‐scale sedimentation events that store and slowly release sediment on floodplains. Large sediment waves composed of relatively fine material and limited bed armoring tend to be right‐skewed owing to rapid vertical readjustments relative to slow lateral recruitment of stored sediment. A revised right‐skewed conceptual model of large sediment and bed waves is presented that fits modern observations and incorporates stochastic elements of flood events. Large sediment waves may be linked to legacy sediment; that is, large repositories of anthropogenic alluvium stored on valley bottom floodplains, wetlands, mill ponds, and reservoirs. This illustrates the ubiquity and importance of secular sediment waves to river management.
Revisiting the Medieval Black Death of 1347–1351: Spatiotemporal Dynamics Suggestive of an Alternate Causation
Authors: Welford Mark , Bossak Brian H.
Published: June 2010

Recent research points to multiple inconsistencies regarding modernYersinia pestis(in Bubonic, Pneumonic, or Septicemic Plague variants) as a causative agent for the Medieval Black Death (MBD). Published arguments at odds with aY. pestis‐caused epidemic include differences in recorded periodicity, seasonal mortality peaks, relevant biogeographical details, genetic findings, and spatiotemporal dynamics, among other inconsistencies. Here, we describe and expand on some of the recent literature noting these items. In addition, we discuss preliminary research related to our recently published theory, in which we agree with research suggesting that the MBD was caused by a virus, not a bacterium, and elucidate our contention that seasonal changes and medieval human trade patterns controlled the timing of peak mortality during the MBD and subsequent ‘plagues’. Epidemic evidence from the first epidemic wave and later outbreaks is presented in support of our hypothesis.
The Design and Experimental Validation of an Ultrafast Shape Memory Alloy ResetTable (SMART) Latch
Authors: Redmond John A. , Brei Diann , Luntz Jonathan , Browne Alan L. , Johnson Nancy L. , Strom Kenneth A.
Published: June 2010

Latches are essential machine elements utilized by all sectors (military, automotive, consumer, manufacturing, etc.) with a growing need for active capabilities such as automatic release and reset, which require actuation. Shape memory alloy (SMA) actuation is an attractive alternative technology to conventional actuation (electrical, hydraulic, etc.) because SMA, particularly in the wire form, is simple, inexpensive, lightweight, and compact. This paper introduces a fundamental latch technology, referred to as the T-latch, which is driven by an ultrafast SMA wire actuator that employs a novel spool-packaged architecture to produce the necessary rotary release motion within a compact footprint. The T-latch technology can engage passively, maintain a strong structural connection in multiple degrees of freedom with zero power consumption, actively release within a very short timeframe (<20 ms, utilizing the SMA spooled actuator), and then repeat operation with automatic reset. The generic architecture of the T-latch and governing operational behavioral models discussed within this paper provide the background for synthesizing basic active latches across a broad range of applications. To illustrate the utility and general operation of the T-latch, a proof-of-concept prototype was designed, built, and experimentally characterized regarding the basic functions of engagement, retention, release, and reset for a common case study of automotive panel lockdown. Based on the successful demonstration and model validation presented in this study, the T-latch demonstrates its promise as an attractive alternative technology to conventional technologies with the potential to enable simple, low-cost, lightweight, and compact active latches across a broad range of industrial applications.
Calculation of General Static Load-Carrying Capacity for the Design of Four-Contact-Point Slewing Bearings
Authors: Aguirrebeitia Josu , Avilés Rafael , Fernández de Bustos Igor , Abasolo Mikel
Published: June 2010

This paper presents a calculation of the general static load-carrying capacity of four-contact-point slewing bearings under axial, radial, and tilting-moment loads. This calculation is based on a generalization of Sjoväll and Rumbarger’s equations and provides an acceptance surface in the load space. This acceptance surface provides a solid basis to compute acceptance curves for the design and selection of bearings of this kind.
Variable Sensitivity-Based Deterministic Robust Design for Nonlinear System
Authors: Lu XinJiang , Li Han-Xiong , Chen C. L. Philip
Published: June 2010

In this paper, a novel robust design approach is proposed to design the robustness of the nonlinear system under large uncontrollable variation. First, a variable sensitivity approach is proposed to formulate the nonlinear effect into the variable sensitivity matrix. Then, a variable sensitivity-based robust design is developed to minimize the variable sensitivity matrix so that the influence of the uncontrollable variation to the performance will be minimized. Since the proposed robust design considers the influence of the nonlinear term in a large design region, it can effectively improve the robustness of the nonlinear system despite large uncontrollable variation. Simulation examples have demonstrated the effectiveness of the proposed design method.
Investigation of three radiation detectors for accurate measurement of absorbed dose in nonstandard fields
Authors: Chung Eunah , Bouchard Hugo , Seuntjens Jan
Published: June 2010

Purpose

To establish accurate experimental dosimetry techniques for reference dose measurements in nonstandard composite fields.

Methods

A cylindrical PMMA phantom filled with water was constructed, at the center of which reference absorbed dose to water for a head and neck IMRT delivery was measured. Based on the proposed new formalism for reference dosimetry of nonstandard fields [Alfonso et al., Med. Phys. 35, 5179–5186 (2008)], a candidate plan‐class specific reference (pcsr) field for a typical head and neck IMRT delivery was created on the CT images of the phantom. The absorbed dose to water in the pcsr field normalized to that in a reference field was measured using three radiation detectors: Gafchromic® EBT films, a diamond detector, and a guarded liquid‐filled ionization chamber developed in‐house (GLIC‐03). Pcsr correction factors were determined for five different types of air‐filled ionization chambers (Exradin A12, NE2571, Exradin A1SL, Exradin A14, and PinPoint® 31006) in a fully rotated delivery and in a delivery with the same MLC settings and weights but from a single gantry angle (a collapsed delivery).

Results

The combined standard uncertainty in measuring the correction factor using the three dosimetry techniques was 0.3%. For all the air‐filled ionization chambers and the pcsr field tested, the correction factor was not different from unity by more than ±0.8%. For the fully rotated delivery, the correction factors were in a narrow range of 0.9955–0.9986, while in the collapsed delivery, they were in a slightly broader range of 0.9922–1.0048. In the collapsed delivery, the Farmer‐type chambers (Exradin A12 and NE2571) had very similar correction factors (0.9922 and 0.9931, respectively), whereas the correction factors for the smaller chambers showed more distinct chamber‐type dependence.

Conclusions

The authors have established three experimental dosimetry techniques that allow reference measurements of nonstandard field correction factors for air‐filled ionization chambers at the 0.3% uncertainty level. These techniques can be used to determine criteria for the selection of plan‐class specific reference fields and ultimately improve clinical reference dosimetry of nonstandard fields.
Generalized fractal dimensions of laser Doppler flowmetry signals recorded from glabrous and nonglabrous skin
Authors: Buard Benjamin , Mahé Guillaume , Chapeau‐Blondeau François , Rousseau David , Abraham Pierre , Humeau Anne
Published: June 2010

Purpose

The technique of laser Doppler flowmetry (LDF) is commonly used to have a peripheral view of the cardiovascular system. To better understand the microvascular perfusion signals, the authors herein propose to analyze and compare the complexity of LDF data recorded simultaneously in glabrous and nonglabrous skin. Glabrous zones are physiologically different from the others partly due to the presence of a high density of arteriovenous anastomoses.

Methods

For this purpose, a multifractal analysis based on the partition function and generalized fractal dimensions computation is proposed. The LDF data processed are recorded simultaneously on the right and left forearms and on the right and left hand palms of healthy subjects. The signal processing method is first tested on a multifractal binomial measure. The generalized fractal dimensions of the normalized LDF signals are then estimated. Furthermore, for the first time, the authors estimate the generalized fractal dimensions from a range of scales corresponding to factors influencing the microcirculation flow (cardiac, respiratory, myogenic, neurogenic, and endothelial).

Results

Different multifractal behaviors are found between normalized LDF signals recorded in the forearms and in the hand palms of healthy subjects. Thus, the variations in the estimated generalized fractal dimensions of LDF signals recorded in the hand palms are higher than those of LDF signals recorded in the forearms. This shows that LDF signals recorded in glabrous zones may be more complex than those recorded in nonglabrous zones. Furthermore, the results show that the complexity in the hand palms could be more important at scales corresponding to the myogenic control mechanism than at the other studied scales.

Conclusions

These findings suggest that the multifractality of the normalized LDF signals is different on glabrous and nonglabrous skin. This difference may rely on the density of arteriovenous anastomoses and differences in nerve supply or biochemical properties. This study provides useful information for an in‐depth understanding of LDF data and a more detailed knowledge of the peripheral cardiovascular system.
Monte Carlo calculation of dosimetry parameters for the IR08‐ brachytherapy source
Authors: Saidi Pooneh , Sadeghi Mahdi , Shirazi Alireza , Tenreiro Claudio
Published: June 2010

Purpose

For the treatment of some cancerous tumors using brachytherapy methods and low‐energy photon sources, such as and , the American Association of Physicists in Medicine Task Group No. 43U1 report recommends that the dosimetric parameters of a new brachytherapy source must be determined in two experimental and Monte Carlo theoretical methods before using each new source clinically. This study presents the results of Monte Carlo calculations of the dosimetric parameters for IR08‐ brachytherapy source design. IR08‐ seed has been manufactured at the Agricultural, Medical and Industrial Research School.

Methods

Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate the dosimetry parameters around the source. Three geometric models of the seed, based on different locations of beads inside the titanium capsule, were simulated. The seed contains five resin beads of 0.6 mm diameter having uniformly absorbed in the bead volume, which were contained within a cylindrical titanium capsule having 0.8 mm outside diameter and 4.8 mm length.

Results

The Monte Carlo calculated dose rate constant of the IR08‐ seed was found to be . Also in this study, the geometry function , line and point‐source radial dose functions and , and the anisotropy function , have been calculated at distances from 0.25 to 7 cm. The results of these calculations have been compared with measured values for an actual IR08‐ seed.

Conclusions

There are no statistical significant dosimetric differences among the three seed orientations in this study (i.e., ideal, vertical, and diagonal). However, the observed differences between the calculated and measured values could be explained by the measurement uncertainty and the configuration of the resin beads within the capsule and capsule orientation.
Performance evaluation of polycrystalline photoconductors for radiation therapy imaging
Authors: Zhao Qihua , Antonuk Larry E. , El‐Mohri Youcef , Wang Yi , Du Hong , Sawant Amit , Su Zhong , Yamamoto Jin
Published: June 2010

Purpose

Electronic portal imaging devices based on megavoltage (MV), active matrix, flat‐panel imagers (AMFPIs) are presently regarded as the gold standard in portal imaging for external beam radiation therapy. These devices, employing indirect detection of incident radiation by means of a metal plate plus phosphor screen combination, offer a quantum efficiency of only at 6 MV, leading to a detective quantum efficiency (DQE) of only . In order to significantly improve the DQE performance of MV AMFPIs, a strategy based on the development of direct detection imagers incorporating thick films of polycrystalline mercuric iodide photoconductor was undertaken and is reported.

Methods

Two MV AMFPI prototypes, one incorporating an thick layer created through physical vapor deposition (PVD) and a second incorporating an thick layer created through screen‐printing of particle‐in‐binder (PIB) material, were quantitatively evaluated using a 6 MV photon beam. The reported measurements include empirical determination of x‐ray sensitivity, lag, modulation transfer function (MTF), noise power spectrum, and DQE.

Results

For both prototypes, MTF and DQE results were found to be consistent with theoretical expectations and the MTFs were also found to be higher than that measured from a conventional MV AMFPI. In addition, the DQE results exhibit input‐quantum‐limited behavior, even at extremely low doses. Compared to PVD, the PIB prototype exhibits much lower dark current, slightly higher lag, and similar DQE. Finally, the challenges associated with this approach, as well as strategies for achieving considerably higher DQE through thicker layers, are discussed.

Conclusions

The DQE of each of the prototypes is found to be comparable to that of conventional MV AMFPIs, commensurate with the modest photoconductor thicknesses of these early samples. It is anticipated that thicker layers of based on PIB deposition can provide higher DQE while maintaining good material properties.
Assessment of the individual fracture risk of the proximal femur by using statistical appearance models
Authors: Schuler Benedikt , Fritscher Karl D. , Kuhn Volker , Eckstein Felix , Link Thomas M. , Schubert Rainer
Published: June 2010

Purpose

Standard diagnostic techniques to quantify bone mineral density (BMD) include dual‐energy x‐ray absorptiometry (DXA) and quantitative computed tomography. However, BMD alone is not sufficient to predict the fracture risk for an individual patient. Therefore, the development of tools, which can assess the bone quality in order to predict individual biomechanics of a bone, would mean a significant improvement for the prevention of fragility fractures. In this study, a new approach to predict the fracture risk of proximal femora using a statistical appearance model will be presented.

Methods

100 CT data sets of human femur cadaver specimens are used to create statistical appearance models for the prediction of the individual fracture load (FL). Calculating these models offers the possibility to use information about the inner structure of the proximal femur, as well as geometric properties of the femoral bone for FL prediction. By applying principal component analysis, statistical models have been calculated in different regions of interest. For each of these models, the individual model parameters for each single data set were calculated and used as predictor variables in a multilinear regression model. By this means, the best working region of interest for the prediction of FL was identified. The accuracy of the FL prediction was evaluated by using a leave‐one‐out cross validation scheme. Performance of DXA in predicting FL was used as a standard of comparison.

Results

The results of the evaluative tests demonstrate that significantly better results for FL prediction can be achieved by using the proposed model‐based approach than using DXA‐BMD for the prediction of fracture load.

Conclusions

The results of the evaluation show that the presented model‐based approach is very promising and also comparable to studies that partly used higher image resolutions for bone quality assessment and fracture risk prediction.
Accuracy estimation for projection‐to‐volume targeting during rotational therapy: A feasibility study
Authors: Long Yong , Fessler Jeffrey A. , Balter James M.
Published: June 2010

Purpose

Estimating motion and deformation parameters from a series of projection radiographs acquired during arc therapy using a reference CT volume has become a promising technique for targeting treatment. The purpose of this work is to investigate the influence of rotational arc length on maximum achievable accuracy of motion estimation.

Methods

The projection‐to‐volume alignment procedure used a nonrigid model to describe motion in thorax area, a cost function consisting of a least‐squared error metric and a simple regularizer that encourages local invertibility, and a four‐level multiresolution scheme with a conjugate gradient method to optimize the cost function. The authors tested both small and large scale deformations typically found in the thorax of a radiotherapy patient at different breathing states and limited‐angle scans of six angular widths (12°, 18°, 24°, 36°, 60°, and 90°) centered at three angles (0°, 45°, and 90°).

Results

The experiments illustrate the potential accuracy of limited‐angle projection‐to‐volume alignment. Registration accuracy can be sensitive to angular center, tends to be lower along direction of the projection set, and tends to decrease away from the rotation center. The studies of small as well as large but realistically scaled deformations show similar dependencies. These trends appear to have fairly low sensitivity to quantum noise effects.

Conclusions

There is potentially sufficient information present in a small spread of projections to monitor the configuration of reasonably high contrast tumors without implanted markers.
Simulation study on the heating of the surrounding anatomy during transurethral ultrasound prostate therapy: A 3D theoretical analysis of patient safety
Authors: Burtnyk Mathieu , Chopra Rajiv , Bronskill Michael
Published: June 2010

Purpose

MRI‐guided transurethral ultrasound therapy can generate highly accurate volumes of thermal coagulation conforming to 3D human prostate geometries. This work simulated, quantified, and evaluated the thermal impact of these treatments on the rectum, pelvic bone, neurovascular bundles (NVBs), and urinary sphincters because damage to these structures can lead to complications.

Methods

Twenty 3D anatomical models of prostate cancer patients were used with detailed bioacoustic simulations incorporating an active feedback algorithm which controlled a rotating, planar ultrasound transducer (17, elements, ). Heating of the adjacent surrounding anatomy was evaluated at 4.7, 9.7, and 14.2 MHz using thermal tolerances reported in literature.

Results

Heating of the rectum posed the most important safety concern, influenced largely by the water temperature of an endorectal cooling device (ECD); depending on anatomy, temperatures of were required to limit potential damage to less than on the outer 1 mm layer of the rectal wall. Heating of the pelvic bone could be important at 4.7 MHz. A smaller sized ECD or a higher ultrasound frequency in sectors where the bone was less than 10 mm from the prostate reduced heating in all cases below the threshold for irreversible damage. Heating of the NVB was significant in 75% of the patient models in the absence of treatment planning; this proportion was reduced to 5% by increasing treatment margins up to 4 mm. To avoid damaging the urinary sphincters, the transducer should be positioned at least 2–4 mm from the sphincters, depending on the transurethral cooling temperature.

Conclusions

Simulations show that MRI‐guided transurethral therapy can treat the prostate accurately, but in the absence of treatment planning, some thermal impact can be predicted on the surrounding anatomy. Treatment planning strategies have been developed, which reduce thermal injury to the surrounding anatomy.
Repeatability in computer‐aided diagnosis: Application to breast cancer diagnosis on sonography
Authors: Drukker Karen , Pesce Lorenzo , Giger Maryellen
Published: June 2010

Purpose

The aim of this study was to investigate the concept of repeatability in a case‐based performance evaluation of two classifiers commonly used in computer‐aided diagnosis in the task of distinguishing benign from malignant lesions.

Methods

The authors performed bootstrap analyses using a data set of 1251 sonographic lesions of which 212 were malignant. Several analyses were performed investigating the impact of sample size and number of bootstrap iterations. The classifiers investigated were a Bayesian neural net (BNN) with five hidden units and linear discriminant analysis (LDA). Both used the same four input lesion features. While the authors did evaluate classifier performance using receiver operating characteristic (ROC) analysis, the main focus was to investigate case‐based performance based on the classifier output for individual cases, i.e., the classifier outputs for each test case measured over the bootstrap iterations. In this case‐based analysis, the authors examined the classifier output variability and linked it to the concept of repeatability. Repeatability was assessed on the level of individual cases, overall for all cases in the data set, and regarding its dependence on the case‐based classifier output. The impact of repeatability was studied when aiming to operate at a constant sensitivity or specificity and when aiming to operate at a constant threshold value for the classifier output.

Results

The BNN slightly outperformed the LDA with an area under the ROC curve of 0.88 versus 0.85 . In the repeatability analysis on an individual case basis, it was evident that different cases posed different degrees of difficulty to each classifier as measured by the by‐case output variability. When considering the entire data set, however, the overall repeatability of the BNN classifier was lower than for the LDA classifier, i.e., the by‐case variability for the BNN was higher. The dependence of the by‐case variability on the average by‐case classifier output was markedly different for the classifiers. The BNN achieved the lowest variability (best repeatability) when operating at high sensitivity and low specificity , while the LDA achieved this at moderate sensitivity and specificity . When operating at constant 90% sensitivity or constant 90% specificity, the width of the 95% confidence intervals for the corresponding classifier output was considerable for both classifiers and increased for smaller sample sizes. When operating at a constant threshold value for the classifier output, the width of the 95% confidence intervals for the corresponding sensitivity and specificity ranged from 9 percentage points (pp) to 30 pp.

Conclusions

The repeatability of the classifier output can have a substantial effect on the obtained sensitivity and specificity. Knowledge of classifier repeatability, in addition to overall performance level, is important for successful translation and implementation of computer‐aided diagnosis in clinical decision making.
Volume‐of‐interest (VOI) imaging in C‐arm flat‐detector CT for high image quality at reduced dose
Authors: Kolditz Daniel , Kyriakou Yiannis , Kalender Willi A.
Published: June 2010

Purpose

A novel method for flat‐detector computed tomography was developed to enable volume‐of‐interest (VOI) imaging at high resolution, low noise, and reduced dose. For this, a full low‐dose overview (OV) scan and a local high‐dose scan of a VOI are combined.

Methods

The first scan yields an overview of the whole object and enables the selection of an arbitrary VOI. The second scan of that VOI assures high image quality within the interesting volume. The combination of the two consecutive scans is based on a forward projection of the reconstructed OV volume that was registered to the VOI. The artificial projection data of the OV scan are combined with the measured VOI data in the raw data domain. Different projection values are matched by an appropriate transformation and weighting. The reconstruction is performed with a standard Feldkamp‐type algorithm. In simulations, the combination of OV scan and VOI scan was investigated on a mathematically described phantom. In measurements, spatial resolution and noise were evaluated with image quality phantoms. Modulation transfer functions and noise values were calculated. Measurements of an anthropomorphic head phantom were used to validate the proposed method for realistic applications, e.g., imaging stents. In Monte Carlo simulations, 3D dose distributions were calculated and dose values were assessed quantitatively.

Results

By the proposed combination method, an image is generated which covers the whole object and provides the VOI at high image quality. In the OV image, a resolution of 0.7 lp/mm (line pairs per millimeter) and noise of 63.5 HU were determined. Inside the VOI, resolution was increased to 2.4 lp/mm and noise was decreased to 18.7 HU. For the performed measurements, the cumulative dose was significantly reduced in comparison to conventional scans by up to 93%. The dose of a high‐quality scan, for example, was reduced from 97 to less than 7 mGy, while keeping image quality constant within the VOI.

Conclusions

The proposed VOI application with two scans is an effective way to ensure high image quality within the VOI while simultaneously reducing the cumulative patient dose.
Dosimetric consequences of misalignment and realignment in prostate 3DCRT using intramodality ultrasound image guidance
Authors: Fraser Danielle J. , Chen Yong , Poon Emily , Cury Fabio L. , Falco Tony , Verhaegen Frank
Published: June 2010

Purpose: It is common practice to correct for interfraction motion by shifting the patient from reference skin marks to better align the internal target at the linear accelerator's isocenter. Shifting the patient away from skin mark alignment causes the radiation beams to pass through a patient geometry different from that planned. Yet, dose calculations on the new geometry are not commonly performed. The intention of this work was to compare the dosimetric consequences of treating the patient with and without setup correction for the common clinical scenario of prostate interfraction motion.

Methods: In order to account for prostate motion, 32 patients initially aligned to the room lasers via skin marks were realigned under the treatment beams by shifting the treatment couch based on ultrasound image guidance. An intramodality 3D ultrasound image guidance system was used to determine the setup correction, so that errors stemming from different tissue representations on different imaging modalities were eliminated. Two scenarios were compared to the reference static treatment plan: (1) Uncorrected patient alignment and (2) corrected patient alignment. Prostate displacement statistics and the dose to the clinical target volume (CTV), bladder, and rectum are reported. Monte Carlo dose calculation methods were employed.

Results: Comparing the uncorrected and corrected scenarios using the static treatment plan as the reference, the average percent difference in for the CTV improved from −5.1% (range −40%, 1.3%) to 0.0% (−3.5%, 2.0%) and the average percent difference in for the bladder and rectum changed from −11% (−84%, 232%) to −8.3% (−61%, 5.2%) and from −47% (−100%, 108%) to 0.9% (−62%, 102%), respectively. There was no simple correlation between displacement and dose discrepancy before correction. After patient realignment, the prescribed dose to the CTV was achieved within 1% for 75% (24/32) of the patients. After patient realignment, 50% of the patients had doses that differed from the static treatment plan by 25% for the bladder and 8% for the rectum.

Conclusions: The dose degradation due to prostate motion (before correction) is not accurately predicted from the average trends for all patients. Outliers included smaller displacements that lead to larger dosimetric differences in the corrected scenario, especially for the bladder and rectum, which exhibited doses substantially different from that planned.
Effect of multileaf collimator‐defined segment size on
Authors: Alaei Parham , Higgins Patrick
Published: June 2010

Purpose

Tertiary multileaf collimators (MLCs) in certain linear accelerators have been found to influence the factor . This effect on is often ignored at the time of commissioning and beam data collection since the scatter/output factors are usually measured with the MLCs retracted. This may be a negligible effect for majority of conventional radiotherapy portals since the jaws are set to conform with MLCs as closely as possible. In the case of IMRT treatments, however, the jaw is often set at a fixed size, and the MLCs form the segments, or control points, of each beam, thus the difference between MLC and jaw settings may be significant.

Methods

The authors quantified the magnitude of this scatter difference for various field sizes defined by MLCs and jaws and characterized the variation in this scatter with MLC and jaw settings. They measured and factors for square fields (apertures) of different sizes for jaw settings from to .

Results

The data indicate that the larger the difference between MLC‐defined aperture and jaw settings, the more significant the difference between the output factors. The authors fitted curves to the MLC output factors for any given jaw size in order to parametrize this aperture effect as a function of jaw and MLC setting.

Conclusions

The quantification of the change in the output factor due to MLCs may be important for better modeling of dose in IMRT deliveries and other applications such asin vivo dosimetry.
Fast simulation of yttrium‐90 bremsstrahlung photons with GATE
Authors: Rault Erwann , Staelens Steven , Van Holen Roel , De Beenhouwer Jan , Vandenberghe Stefaan
Published: June 2010

Purpose

Multiple investigators have recently reported the use of yttrium‐90 bremsstrahlung single photon emission computed tomography (SPECT) imaging for the dosimetry of targeted radionuclide therapies. Because Monte Carlo (MC) simulations are useful for studying SPECT imaging, this study investigates the MC simulation of bremsstrahlung photons in SPECT. To overcome the computationally expensive simulation of electrons, the authors propose a fast way to simulate the emission of bremsstrahlung photons based on prerecorded bremsstrahlung photon probability density functions (PDFs).

Methods

The accuracy of bremsstrahlung photon simulation is evaluated in two steps. First, the validity of the fast bremsstrahlung photon generator is checked. To that end, fast and analog simulations of photons emitted from a point source in a water phantom are compared. The same setup is then used to verify the accuracy of the bremsstrahlung photon simulations, comparing the results obtained with PDFs generated from both simulated and measured data to measurements. In both cases, the energy spectra and point spread functions of the photons detected in a scintillation camera are used.

Results

Results show that the fast simulation method is responsible for a 5% overestimation of the low‐energy fluence (below 75 keV) of the bremsstrahlung photons detected using a scintillation camera. The spatial distribution of the detected photons is, however, accurately reproduced with the fast method and a computational acceleration of ‐fold is achieved. When measured PDFs are used in the simulations, the simulated energy spectrum of photons emitted from a point source of in a water phantom and detected in a scintillation camera closely approximates the measured spectrum. The PSF of the photons imaged in the 50–300 keV energy window is also accurately estimated with a 12.4% underestimation of the full width at half maximum and 4.5% underestimation of the full width at tenth maximum.

Conclusions

Despite its limited accuracy, the fast bremsstrahlung photon generator is well suited for the simulation of bremsstrahlung photons emitted in large homogeneous organs, such as the liver, and detected in a scintillation camera. The computational acceleration makes it very useful for future investigations of bremsstrahlung SPECT imaging.
The Italian affair: The employment of parallel‐plate ionization chambers for dose measurements in high dose‐per‐pulse IORT electron beams
Authors: Cella L. , Liuzzi R. , Salvatore M.
Published: June 2010

Purpose

At the high dose‐per‐pulse rates used by some intraoperative radiotherapy (IORT) units, the employment of ionization chambers for dose measurements needs an appropriate correction for ion recombination. Through a revision of the existing literature, the authors compared different methods for the determination of the recombination correction factor and their impact on clinical dosimetry.

Methods

A dosimetric characterization of IORT electron beams from a Linac Hitesys Novac7 (Aprilia‐Latina, Italy) was performed. Dose‐to‐water values were measured with dose‐per‐pulse independent chemical dosimeters (operated by the Italian Primary Standard Dosimetry Laboratory, ENEA) and compared to doses obtained by two different parallel‐plate ionization chamber models (Markus and Advanced Markus, PTW, Freiburg, Germany). For dose measurements using ionization chambers, the authors applied two different methods for the determination of the ion recombination correction factor , as suggested in previous articles. The first method is based on the experimental estimation of the free‐electron fraction values ; the second one is based on the “nonstandard” two‐voltage analysis including the free‐electron component.

Results

For a Markus type chamber, there is a good agreement between the results on and those reported in the literature for both methods, while for the Advanced Markus chamber, no data are available for comparison.

Conclusions

Comparing values of obtained by dose‐per‐pulse independent dosimeters and by ionization chambers measurements corrected using the two different approaches, the authors can conclude that the factor determination is very critical and that only an experimental protocol using ionization chamber intercalibration can be considered reliable.