bluuebunny/crossref_metadata_2025 huggingface dataset:
Demographic Change in European Towns 2001–11: A Cross‐National Multi‐Level Analysis
Authors: Smith Ian
Published: February 2017

The unique contribution of this paper is to empirically compare and contrast demographic change in settlements with a population between 5,000 and under 50,000 (defined as towns) across different national urban systems in Europe with common definitions for the first time. The analysis uses a new data set based on harmonised small area data and harmonised morphological definitions of what a town is. The paper hypothesises first that a general model of demographic growth can be applied across national urban systems and secondly that regional demographic change is a significant predictor of demographic change in towns nested within those regions within this generalised model. A fixed effect multi‐level regression analysis tests the importance of town‐level and regional factors among towns from five national systems but also within two individual national urban systems. The findings suggest that national context still matters and within some national systems, regional context also strongly predicts demographic change in towns.
Tolerance, Intergroup Contacts and Municipal‐Spatial Organisation: The Case of Jews and Arab Palestinians in the Tel‐Aviv Metropolitan Area
Authors: Omer Itzhak , Goldblatt Ran , Romann Michael , Khamaisi Rassem
Published: February 2017

The paper examines the willingness of Israeli Jews and Arab Palestinians for intergroup contacts during daily activities in diverse functional spaces and spatial organisational contexts within the metropolitan area of Tel‐Aviv, Israel. Semi‐structured interviews were conducted among visitors to public spaces in three mixed Arab‐Jewish areas: a mixed city; two adjacent Jewish and Arab suburban townships; and two relatively distant Jewish and Arab towns. The research findings indicate that higher‐order functional spaces (e.g. shopping mall), municipal separation and relatively large geographic distance between Jewish and Arab towns enhance willingness for inter‐group contacts, feelings of comfort and security and a shared ethnic identity of sites. We relate this tendency to the unique geographic distribution of Jewish and Arab localities in Israel which allows the separation between functional and residential spaces and thus a reduction of feelings of threat and discomfort experienced upon inter‐group exposure and contact.
Deprivation and the Rural‐Urban Trap
Authors: Dymitrow Mirek , Biegańska Jadwiga , Grzelak‐Kostulska Elżbieta
Published: February 2017

Departing from the idea that cultural mechanisms are capable of allowing for conceptual dichotomies to create oppression, this paper challenges the engrained tradition of using ‘urban/rural’ as guiding labels in societal organisation when seen through the prism of deprivation. Two Polish deprivation‐ridden estates – one ‘urban’ and one ‘rural’ – were investigated. Having taken account of the residents’ everyday lives in the socio‐economic, material and discursive dimensions, our findings indicate that the notions of rurality and urbanity imbricate and leapfrog meaningful territories at the local level. Realising the danger of deploying stereotypes as beacons in governance, from this richly contextualised account we draw that many problems today are space‐independent and cannot be attenuated by following development paths reinvented in the name of empirically questionable yet culturally sustained and politically ontologised spatialities. This, then, calls for rethinking both the discursivity and the elusiveness of rural‐urban thinking in the context of deprivation.
Cover Image, Volume 15, Issue 1
Authors: Treggiari E. , Ressel L. , Polton G. A. , Benoit J. , Desmas I. , Blackwood L.
Published: February 2017

The cover image, by E. Treggiari et al., is based on the Original Article Clinical outcome, PDGFRß and KIT expression in feline histiocytic disorders: a multicentre study, DOI: 10.1111/vco.12142.

image
The glocalization of English in the Pakistan linguistic landscape
Authors: MANAN SYED ABDUL , DAVID MAYA KHEMLANI , DUMANIG FRANCISCO PERLAS , CHANNA LIAQUAT ALI
Published: February 2017

This study surveys the linguistic landscape in a particular area of Pakistan, and explores the use of languages, and the pervasiveness of English in the localized non‐Roman script. Although English functions as a foreign language for most Pakistanis, it occurs extensively in signage in public places. Following the analysis of multiple data sources such as interviews of businesspeople and photographs of private signboards/billboards, wall advertisements, roadside signposts and posters, the results suggest that Englishized Urdu and Urduized English predominate in the linguistic landscape, while local/indigenous languages remain completely absent.
Selecting an Appropriate Strategy to Increase Petrochemical Product Sales (Case Study: Iranian Petrochemical Industry)
Authors: Shahmirzadi H. Esmaeili
Published: February 2017

This article aims to find the best strategies which help increase petrochemical products sales in Iran using multivariate regression model, Grand Strategy Matrix (GSM), and SWOT matrix. Market Development, Market Penetration, Product Development by creating and developing chemical cities or parks, petro-chemical refineries, and Especial Economic Zones, Vertical Integration, and Concentric Diversification with Diverse Portfolio were considered independent variables, while Increasing Petrochemical Product Sales is dependent variable. Then, each of above mentioned factors affecting the sales were ranked in order to take advantage of the highest added-value. The statistical population consisted of 140 experts, managers, directors, and customers involved in National Iranian Gas Company and Iran Petrochemical Company. Random sampling method was employed. A total of 57experts, managers, directors, and customers were enrolled as sample size. Data were collected using a five-option Likert scale questionnaire. SPSS, Grand Strategy Matrix (GSM), and SWOT[1] matrix were employed to analyze the data. According to the Cronbach's alpha (0.86), the reliability was verified. Market Development, Market Penetration, Product Development, and Concentric Diversification with Diverse Portfolio were found to be suitable offensive strategies to increase the petrochemical product sales. Product Development and Market Penetration are the most effective factors in increasing the petrochemical product sales. Therefore, they need to be taken into account. [1]Strength, Weakness, Opportunity, Threats
PENSAR Y RE-PENSAR LA PRODUCCIÓN ACADÉMICA EN EL CAMPO DE LAS ARTES: UNA MIRADA DESDE LA PERIFERIA.
Authors: Soto Silva Ignacio , Alvarado Toledo Paola , Ferrada Sullivan Jorge
Published: February 2017

Construimos nuestra reflexión sobre la base de la integración de los campos de investigación científica y el arte, sus prácticas y estrategias metodológicas como medio de unificación de criterios de calidad. Asimismo se comprende que en la situación actual de la Universidad, las dimensiones del desarrollo artístico y su relación con la academia se encuentran tensionadas por la productividad científica y sus cánones de valoración, los cuales se contraponen -en el aquí y ahora- a la lógica de funcionamiento de la creación artística desarrollada en el marco de las Universidades periféricas.

Finalmente no se busca responder las interrogantes, más bien se pretende hacer dialogar posturas teóricas que permitan plantear en las diversas instancias del desarrollo académico actual, una relación dialogante entre el saber sensible del arte, la productividad científica, y sus implicancias en los procesos de valoración académica en docentes de carreras de pregrado asociadas al arte.
A Weakly Nonlinear Approach Based on a Distributed Flame Describing Function to Study the Combustion Dynamics of a Full-Scale Lean-Premixed Swirled Burner
Authors: Laera Davide , Camporeale Sergio M.
Published: February 2017

Modern combustion chambers of gas turbines for power generation and aero-engines suffer of thermo-acoustic combustion instabilities generated by the coupling of heat release rate fluctuations with pressure oscillations. The present article reports a numerical analysis of limit cycles arising in a longitudinal combustor. This corresponds to experiments carried out on the longitudinal rig for instability analysis (LRIA) test facility equipped with a full-scale lean-premixed burner. Heat release rate fluctuations are modeled considering a distributed flame describing function (DFDF), since the flame under analysis is not compact with respect to the wavelengths of the unstable modes recorded experimentally. For each point of the flame, a saturation model is assumed for the gain and the phase of the DFDF with increasing amplitude of velocity fluctuations. A weakly nonlinear stability analysis is performed by combining the DFDF with a Helmholtz solver to determine the limit cycle condition. The numerical approach is used to study two configurations of the rig characterized by different lengths of the combustion chamber. In each configuration, a good match has been found between numerical predictions and experiments in terms of frequency and wave shape of the unstable mode. Time-resolved pressure fluctuations in the system plenum and chamber are reconstructed and compared with measurements. A suitable estimate of the limit cycle oscillation is found.
An Approach for Generating an Average Bone Template With Semantic Parameters
Authors: He Kunjin , Zhang Rongli , Chen Zhengming , Jiang Junfeng , Yuming Zhang
Published: February 2017

To facilitate the design of the serialized implants and to satisfy the requirements of the population, a novel method is put forward for constructing an average bone model (ABM) with semantic parameters as a template. First, the ABM is created from the existing bone models, among which each bone has an equal contribution to the ABM. Second, combined with medical semantics, some characteristic points and semantic parameters are defined on the ABM, and then, parameter values for each bone can be automatically obtained through its registration and deformation to the ABM. Finally, an average bone template (ABT) is constructed by configuring the semantic parameters and by building the constraints between parameters. Taking 100 femur models as samples, we construct the ABT, and the template can be easily extended to generate a new average template through the given average equation.
An Experimental and Numerical Study to Support Development of Molten Salt Breeder Reactor
Authors: Srivastava A. K. , Chouhan R. , Borgohain A. , Jana S. S. , Maheshwari N. K. , Pilkhwal D. S. , Rama Rao A. , Hareendhran K. N. , Chowdhury S. , Modi K. B. , Raut S. K. , Parida S. C.
Published: February 2017

Conceptual molten salt breeder reactor (MSBR) is under development in Bhabha Atomic Research Centre (BARC) with long-term objective of utilizing abundant thorium available in India. It is based on molten salts, which acts as fuel, blanket, and coolant for the reactor. LiF–ThF4 (77.6–22.4 mol %) is proposed as a blanket salt for Indian MSBR. A laboratory scale molten salt natural circulation loop (MSNCL) named molten active fluoride salt loop (MAFL) has been setup for thermal-hydraulic, material compatibility, and chemistry control studies. Steady-states and transient experiments have been performed in the operating temperature range of 600–750 °C. The loop operates in the power range of 250–550 W. Steady-state correlation given for natural circulation flow in a loop is compared with the steady-state experimental data. The Reynolds number was found to be in the range of 57–114. Computation fluid dynamics (CFD) simulation has also been performed for MAFL using openfoam code, and the results are compared with the experimental data generated in the loop. It has been found that predictions of openfoam are in good agreement with the experimental data. In this paper, features of the loop, its construction, and the experimental and numerical studies performed are discussed in detail.
Thermal Performance of Miniscale Heat Sink With Jet Impingement and Dimple/Protrusion Structure
Authors: Shen Zhongyang , Jing Qi , Xie Yonghui , Zhang Di
Published: February 2017

Cooling technique in a miniscale heat sink is essential with the development of high-power electronics, such as electronic chip. As heat transfer techniques, jet impingement cooling and convective cooling by roughened surface are commonly adopted. To obtain a good cooling efficiency, the cooling structure within the heat sink should be carefully designed. In the present study, the miniscale heat sink with a feature size of 1–100 mm is setup. Arrangement of the jet impingement and dimple/protrusion surface is designed as heat transfer augmentation approaches. The effect of dimple/protrusion configuration and depth to diameter ratio is discussed. From the result, the heat transfer coefficient h distribution of heat sink surface is demonstrated for each case. The pressure penalty due to the arrangement of roughened structure is evaluated. Also, thermal performance (TP) and performance evaluation plot are adopted as evaluations of cooling performance for each configuration. Comparing all the cases, optimal cooling structure considering the energy-saving performance is obtained for the miniscale heat sink. Referencing the statistics, a new insight has been provided for the design of cooling structure inside the miniscale heat sink.
Mesoscopic Analysis of Dynamic Droplet Behavior on Wetted Flat and Grooved Surface for Low Viscosity Ratio
Authors: Bhardwaj Saurabh , Dalal Amaresh
Published: February 2017

In the present study, the interfacial dynamics of displacement of three-dimensional spherical droplet on a rectangular microchannel wall considering wetting effects are studied. The two-phase lattice Boltzmann Shan−Chen model is used to explore the physics. The main focus of this study is to analyze the effect of wettability, low viscosity ratio, and capillary number on the displacement of spherical droplet subjected to gravitational force on flat as well as grooved surface of the channel wall. The hydrophobic and hydrophilic natures of wettabilities on wall surface are considered to study for viscosity ratio, M≤1. The results are presented in the form of temporal evolution of wetted length and wetted area for combined viscosity ratios and wettability scenario. In the present study, it is observed that in dynamic droplet displacement, the viscosity ratio and the capillary number play a significant role. It is found that as the viscosity ratio increases, both the wetted area and the wetted length increase and decrease in the case of hydrophilic and hydrophobic wettable walls, respectively. The groove area on the vertical wall tries to entrap fraction of droplet fluid in case of hydrophilic surface of the vertical wall, whereas in hydrophobic case, droplet moves past the groove without entrapment.
Experimental Verification of a Prediction Model for Pool Boiling Enhanced by the Electrohydrodynamic Effect and Surface Wettability
Authors: Kano Ichiro , Okamoto Naoki
Published: February 2017

Enhancing of boiling heat transfer by combining the electrohydrodynamic (EHD) effect and surface wettability has been shown to remove the high heat fluxes from electrical devices such as laser diodes, light emitting diodes, and central processing units. However, this phenomenon is not well understood. Our previous studies on the critical heat flux (CHF) of pool boiling have shown that CHF greatly increases with the application of an electric field and that the wall temperature can be decreased to a level with the safe operation of the electrical devices by using a low contact angle with the boiling surface. To verify the earlier prediction model, CHF enhancement by changing the contact angle with the boiling surface and by the application of an electric field was investigated. A fluorinated dielectric liquid (Asahi Glass Co. Ltd, Tokyo, Japan, AE-3000) was selected as the working fluid. To allow the contact angle between the boiling surface and the dielectric liquid to be changed, several different materials (Cu, Cr, NiB, Sn) and a surface coated with a mixture of 1.5 and 5 μm diamond particles were used as boiling surfaces. The CHFs at different contact angles were 20.5–26.9 W/cm2, corresponding to 95–125% of that for a polished Cu surface (21.5 W/cm2). Upon application of a −5 kV/mm electric field to the microstructured surface (the mixture of 1.5 μm and 5 μm diamond particles), a CHF of 99 W/cm2 at a superheat of 33.5 K was obtained. Based on this experimental evidence, we normalized the CHF and contact angle using our previously developed hydrodynamic instability model and semi-empirical model derived from the interfacial area density close to the boiling surface. This procedure allowed us to develop a general model that predicted CHF well, including the CHF for the de-ionized (DI) water.
Characteristics of Auto-Ignition in Internal Combustion Engines Operated With Gaseous Fuels of Variable Methane Number
Authors: Amador German , Forero Jorge Duarte , Rincon Adriana , Fontalvo Armando , Bula Antonio , Padilla Ricardo Vasquez , Orozco Wilman
Published: February 2017

This paper explores the feasibility of using Syngas with low methane number as fuel for commercial turbocharged internal combustion engines. The effect of methane number (MN), compression ratio (CR), and intake pressure on auto-ignition tendency in spark ignition internal combustion engines was determined. A nondimensional model of the engine was performed by using kinetics mechanisms of 98 chemical species in order to simulate the combustion of the gaseous fuels produced from different thermochemical processes. An error function, which combines the Livengood–Wu with ignition delay time correlation, to estimate the knock occurrence crank angle (KOCA) was proposed. The results showed that the KOCA decreases significantly as the MN increases. Results also showed that Syngas obtained from coal gasification is not a suitable fuel for engines because auto-ignition takes place near the beginning of the combustion phase, but it could be used in internal combustion engines with reactivity controlled compression ignition (RCCI) technology. For the case of high compression ratio and a high inlet pressure at the engine's manifold, fuels with high MN are suitable for the operating conditions proposed.
Influence of Key Structural Parameters of Combustion Chamber on the Performance of Diesel Engine
Authors: Li Xinhai , Cheng Yong , Ji Shaobo , Lan Xin
Published: February 2017

The structural parameters of combustion chamber have great impacts on the process of air–fuel mixing, combustion, and emissions of diesel engine. The dynamic characteristics and emission performances could be improved by means of optimizing the parameters of the combustion chamber. In this paper, the key structure of a diesel engine combustion chamber is parameterized, and the influence of individual structural parameter on dynamic characteristics and emissions of the engine is simulated and analyzed by computational fluid dynamics (CFD) software avl-fire. The results show that under constant compression ratio, the in-cylinder peak pressure decreases with increasing inclination angle of the combustion chamber (α), while the height (Tm) and bowl radius (R) have little influence on the in-cylinder peak pressure. With increasing α, NO emissions decrease, and soot emissions first increase and then decrease. With increasing R, both NO and soot emissions decrease first and then increase. Therefore, the combustion chamber parameters could be optimized by comprehensive consideration of cylinder pressure, NO and soot emissions.
Percentage depth dose evaluation in heterogeneous media using thermoluminescent dosimetry
Authors: da Rosa L.A.R. , Cardoso S.C. , Campos L.T. , Alves V.G.L. , Batista D.V.S. , Facure A.
Published: February 2017

The purpose of this study is to investigate the influence of lung heterogeneity inside a soft tissue phantom on percentage depth dose (PDD). PDD curves were obtained experimentally using LiF:Mg,Ti (TLD‐100) thermoluminescent detectors and applying Eclipse treatment planning system algorithms Batho, modified Batho (M‐Batho or BMod), equivalent TAR (E‐TAR or EQTAR), and anisotropic analytical algorithm (AAA) for a 15 MV photon beam and field sizes of , and . Monte Carlo simulations were performed using the DOSRZnrc user code of EGSnrc. The experimental results agree with Monte Carlo simulations for all irradiation field sizes. Comparisons with Monte Carlo calculations show that the AAA algorithm provides the best simulations of PDD curves for all field sizes investigated. However, even this algorithm cannot accurately predict PDD values in the lung for field sizes of and . An overdosage in the lung of about 40% and 20% is calculated by the AAA algorithm close to the interface soft tissue/lung for and field sizes, respectively. It was demonstrated that differences of 100% between Monte Carlo results and the algorithms Batho, modified Batho, and equivalent TAR responses may exist inside the lung region for the field.

PACS number: 87.55.kd
An anthropomorphic beating heart phantom for cardiac X‐ray CT imaging evaluation
Authors: Boltz Thomas , Pavlicek William , Paden Robert , Renno Markus , Jensen Angela , Akay Metin
Published: February 2017

The current work describes an anthropomorphic beating heart phantom constructed as a tool for the assessment of technological advances in cardiac X‐ray computed tomography (CT). The phantom is comprised of a thorax, a compressor system, an ECG system, a beating heart with tortuous coronary arteries, and the option to add or remove pathologies such as aberrant beats, stents, and plaques. Initial trials with the phantom have shown its utility to assess temporal resolution, spatial resolution, radiation dose, iodine contrast, stents, and plaques.

PACS numbers: 87.59.Fm, 87.57.Ce
Target and peripheral dose during patient repositioning with the Gamma Knife automatic positioning system (APS) device
Authors: Tran Tuan‐Anh , Stanley Thomas , Malhotra Harish K. , deBoer Steven F. , Prasad Dheerendra , Podgorsak Matthew B.
Published: February 2017

The GammaPlan treatment planning system does not account for the leakage and scatter dose during APS repositioning. In this study, the dose delivered to the target site and its periphery from the defocus stage and intershot couch transit (couch motion from the focus to defocus position and back) associated with APS repositioning are measured for the Gamma Knife model 4C. A stereotactic head‐frame was attached to a Leksell 16 cm diameter spherical phantom with a calibrated ion chamber at its center. Using a fiducial box, CT images of the phantom were acquired and registered in the GammaPlan treatment planning system to determine the coordinates of the target (center of the phantom). An absorbed dose of 10 Gy to the 50% isodose line was prescribed to the target site for all measurements. Plans were generated for the 8, 14 and 18 mm collimator helmets to determine the relationship of measured dose to the number of repositions of the APS system and to the helmet size. The target coordinate was identical throughout entire study and there was no movement of the APS between various shots. This allowed for measurement of intershot transit dose at the target site and its periphery. The couch was paused in the defocus position, allowing defocus dose measurements at the intracranial target and periphery. Measured dose increases with frequency of repositioning and with helmet collimator size. During couch transit, the target receives more dose than peripheral regions; however, in the defocus position, the greatest dose is superior to the target site. The automatic positioning system for the Leksell Gamma Knife model 4C results in an additional dose of up to , and to the target site; its periphery receives additional dose that varies depending on its position relative to the target. There is also dose contribution to the patient in the defocus position, where the APS repositions the patient from one treatment coordinate to another. This may be important for treatment areas around critical structures within the brain. Further characterization of the defocus and transit exposures and development of a dose calculation algorithm to account for these doses would improve the accuracy of the delivered plan.

PACS numbers: 87.53.‐j, 87.53.Bn, 87.53.Dq, 87.53.Ly
Junctioning longitudinally adjacent PTVs with Helical TomoTherapy
Authors: Garcia Lourdes M. , Gerig Lee H. , Raaphorst Peter , Wilkins David
Published: February 2017

Irradiation of longitudinally adjacent PTVs with Helical TomoTherapy (HT) may be clinically necessary, for example in treating a recurrent PTV adjacent to a previously‐treated volume. In this work, the parameters which influence the cumulative dose distribution resulting from treating longitudinally adjacent PTVs are examined, including field width, pitch, and PTV location. In‐phantom dose distributions were calculated for various on‐ and off‐axis cylindrical PTVs and were verified by ion chamber and film measurement. Dose distributions were calculated to cover 95% of the PTV by the prescribed dose using 25 and 50 mm long HT fields with pitches of either 0.3 or 0.45. These dose distributions where then used to calculate the 3D dose distribution in the junction region between two PTVs. The best junction uniformity was obtained for fields of equal width, with larger fields providing better intra‐PTV dose homogeneity than smaller fields. Junctioning fields of different widths resulted in a much larger dose inhomogeneity, but this could be improved significantly by dividing the junction end of the PTV treated with the smaller field into multiple (up to 4) sub‐PTVs, with the prescribed dose in each sub‐PTV decreasing with proximity to the junction region. This provided a PTV matching with dose homogeneity similar to that achieved when junctioning two PTVs, both irradiated by the 50 mm field, and provided a distribution where 95% of the PTV received at least the prescribed dose, with maximum excursions from prescribed dose varying from to . We conclude that junctioning adjacent PTVs is possible. Treating longitudinally adjacent PTVs with different widths is a challenge, but dose uniformity is improved by breaking PTVs into multiple contiguous sub‐PTVs modified to feather (broaden) the effective junctioning region.

PACS number: 87.55.D
Dosimetric study of 2D ion chamber array matrix for the modern radiotherapy treatment verification
Authors: Saminathan Sathiyan , Manickan Ravikumar , Chandraraj Varatharaj , Supe Sanjay. S.
Published: February 2017

Intensity‐modulated radiotherapy treatment demands stringent quality assurance and accurate dose determination for delivery of highly conformal dose to the patients. Generally 3D dose distributions obtained from a treatment planning system have to be verified by dosimetric methods. Mainly, a comparison of two‐dimensional calculated and measured data in several coplanar planes is performed. In principle, there are many possibilities to measure two‐dimensional dose distributions such as films, flat‐panel electronic portal imaging devices (EPID), ion chambers and ionization chamber arrays, and radiographic and radiochromic films. The flat‐panel EPIDs show a good resolution and offer a possibility for real‐time measurements: however to convert the signal into dose, a separate commercial algorithm is required. The 2D ion chamber array system offers the real‐time measurements. In this study, dosimetric characteristics of 2D ion chamber array matrix were analyzed for verification of radiotherapy treatments. The dose linearity and dose rate effect of the I'matriXX device was studied using 6 MV, 18 MV photons and 12 MeV electrons. The output factor was estimated using I'matriXX device and compared with ion chamber measurements. The ion chamber array system was found to be linear in the dose range of 2–500 cGy and the response of the detector was found to be independent of dose rate between to . The estimated relative output factor with I'matriXX was found to match very well with the ion chamber measurements. To check the final dose delivered during IMRT planning, dose distribution patterns such as field‐in‐field, pyramidal, and chair tests were generated with the treatment planning system (TPS) and the same was executed in the accelerator and measured with the I'matriXX device. The dose distribution pattern measured by the matrix device for field‐in‐field, pyramidal, and chair test were found to be in good agreement with the calculated dose distribution by TPS both for 6 and 18 MV photons (γ ≤ 1: 96%, criteria 3%, 3 mm). Two 7‐field IMRT plans (one prostate, one head and neck) dose distribution patterns were also measured with I'matriXX device and compared with film dosimetry. The measurements and evaluation proves that I'matriXX can be used for quantifying absolute dose. Moreover, using I'matriXX as absolute dosimeter in IMRT field verification, avoids the time‐consuming procedure of making ionometric measurement for absolute dose estimation and film for dose distribution verification. The I'matriXX can also used for routine quality assurance checks like flatness, symmetry, field width, and penumbra of the linear accelerator beam.

PACS number: 87.55.ne and 87.56.Fc
Commissioning of a double‐focused micro multileaf collimator (μMLC)
Authors: Fischer Marcus , Todorovic Manuel , Drud Eva , Cremers Florian
Published: February 2017

Double‐focused μMLCs are able to create fields with steeper dose gradients at the field edges and are, therefore, an advancement in delivering stereotactic treatments. A double‐focused μMLC has been installed at a Siemens Primus linear accelerator (linac) as a first research installation in Europe. The basic dosimetric parameters, such as leakage, output factors, depth‐dose curves and penumbra, have been measured in 6 and 15 MV‐mode by use of radiochromic films (GafChromic EBT), ionization chambers and our solid water QA‐phantom (Easy Cube). The leakage between the leaves is minimal and lower than that of most commercially available MLCs. Therefore, the field size of the linac can be kept constant while the leaves of the μMLC are creating different aperture shapes. Percentage depth doses (PDDs) generated by the double‐focused μMLC are equal to depth‐dose curves of the original linac. That means the μMLC affects only the off‐axis ratio (OAR). Based on the fact that the μMLC is double‐focused and the source‐to‐collimator distance is larger, the penumbra is sharper than that for fields defined by the original linac MLC. The mechanical and dosimetric investigations show the benefit of the double‐focused μMLC attached to a Siemens Primus linear accelerator.

PACS number: 87.10.+e
An organ and effective dose study of XVI and OBI cone‐beam CT systems
Authors: Hyer Daniel E. , Serago Christopher F. , Kim Siyong , Li Jonathan G. , Hintenlang David E.
Published: February 2017

The main purpose of this work was to quantify patient organ doses from the two kilovoltage cone beam computed tomography (CBCT) systems currently available on medical linear accelerators, namely the X‐ray Volumetric Imager (XVI, Elekta Oncology Systems) and the On‐Board Imager (OBI, Varian Medical Systems). Organ dose measurements were performed using a fiber‐optic coupled (FOC) dosimetry system along with an adult male anthropomorphic phantom for three different clinically relevant scan sites: head, chest, and pelvis. The FOC dosimeter was previously characterized at diagnostic energies by Hyer et al. [Med Phys 2009;36(5):1711–16] and a total uncertainty of approximately 4% was found for in‐phantom dose measurements. All scans were performed using current manufacturer‐installed clinical protocols and appropriate bow‐tie filters. A comparison of image quality between these manufacturer‐installed protocols was also performed using a Catphan 440 image quality phantom. Results indicated that for the XVI, the dose to the lens of the eye (1.07 mGy) was highest in a head scan, thyroid dose (19.24 mGy) was highest in a chest scan, and gonad dose (29 mGy) was highest in a pelvis scan. For the OBI, brain dose (3.01 mGy) was highest in a head scan, breast dose (5.34 mGy) was highest in a chest scan, and gonad dose (34.61 mGy) was highest in a pelvis scan. Image quality measurements demonstrated that the OBI provided superior image quality for all protocols, with both better spatial resolution and low‐contrast detectability. The measured organ doses were also used to calculate a reference male effective dose to allow further comparison of the two machines and imaging protocols. The head, chest, and pelvis scans yielded effective doses of 0.04, 7.15, and 3.73 mSv for the XVI, and 0.12, 1.82, and 4.34 mSv for the OBI, respectively.

PACS number: 87.57.uq
Quantification and reduction of peripheral dose from leakage radiation on Siemens primus accelerators in electron therapy mode
Authors: Yeboah Collins , Karotki Alex , Hunt Dylan , Holly Rick
Published: February 2017

In this work, leakage radiation from EA200 series electron applicators on Siemens Primus accelerators is quantified, and its penetration ability in water and/or the shielding material Xenolite‐NL established. Initially, measurement of leakage from applicators was performed as a function of height along applicator and of lateral distance from applicator body. Relative to central‐axis ionization maximum in solid water, the maximum leakage in air observed with a cylindrical ion chamber with 1 cm solid water buildup cap at a lateral distance of 2 cm from the front and right sidewalls of applicators were 17% and 14%, respectively; these maxima were recorded for 18 MeV electron beams and applicator sizes of . In the patient plane, the applicator leakage gave rise to a broad peripheral dose off‐axis distance peak that shifted closer to the field edge as the electron energy increases. The maximum peripheral dose from normally incident primary electron beams at a depth of 1 cm in a water phantom was observed to be equal to 5% of the central‐axis dose maximum and as high as 9% for obliquely incident beams with angles of obliquity . Measured depth‐peripheral dose curves showed that the “practical range” of the leakage electrons in water varies from approximately 1.4 to 5.7 cm as the primary electron beam energy is raised from 6 to 18 MeV. Next, transmission measurements of leakage radiation through the shielding material Xenolite‐NL showed a 4 mm thick sheet of this material is required to attenuate the leakage from 9 MeV beams by two‐thirds, and that for every additional 3 MeV increase in the primary electron beam energy, an additional Xenolite‐NL thickness of roughly 2 mm is needed to achieve the aforementioned attenuation level. Finally, attachment of a 1 mm thick sheet of lead to the outer surface of applicator sidewalls resulted in a reduction of the peripheral dose by up to 80% and 74% for 9 and 18 MeV beams, respectively. This sidewall modification had an insignificant effect on the clinical depth dose, cross‐axis beam profiles, and output factors.

PACS numbers: 87.53.Bn, 87.56.bd, 87.56.J‐
Analysis of peripheral doses for base of tongue treatment by linear accelerator and helical TomoTherapy IMRT
Authors: Bennett Brian Richard , Lamba Michael A. S. , Elson Howard R.
Published: February 2017

The purpose of this study was to compare the peripheral doses to various organs from a typical head and neck intensity‐modulated radiation therapy (IMRT) treatment delivered by linear accelerator (linac) and helical TomoTherapy.

Multiple human CT data sets were used to segment critical structures and organs at risk, fused and adjusted to an anthropomorphic phantom. Eighteen contours were designated for thermoluminescent dosimeter (TLD) placement. Following the RTOG IMRT Protocol 0522, treatment of the primary tumor and involved nodes (PTV70) and subclinical disease sites (PTV56) was planned utilizing IMRT to 70 Gy and 56 Gy. Clinically acceptable treatment plans were produced for linac and TomoTherapy treatments. TLDs were placed and each treatment plan was delivered to the anthropomorphic phantom four times.

Within 2.5 cm (one helical TomoTherapy field width) superior and inferior to the field edges, normal tissue doses were on average 45% lower using linear accelerator. Beyond 2.5 cm, the helical TomoTherapy normal tissue dose was an average of 52% lower. The majority of points proved to be statistically different using the Student's t‐test with . Using one method of calculation, probability of a secondary malignancy was 5.88% for the linear accelerator and 4.08% for helical TomoTherapy.

Helical TomoTherapy delivers more dose than a linac immediately above and below the treatment field, contributing to the higher peripheral doses adjacent to the field. At distances beyond one field width (where leakage is dominant), helical TomoTherapy doses are lower than linear accelerator doses.

PACS number: 87.50.cm Dosimetry/exposure assessment
Assessment of a commercially available automatic deformable registration system
Authors: Fallone B. Gino , Rivest D. Ryan C. , Riauka Terence A. , Murtha Albert D.
Published: February 2017

In recent years, a number of approaches have been applied to the problem of deformable registration validation. However, the challenge of assessing a commercial deformable registration system – in particular, an automatic registration system in which the deformable transformation is not readily accessible – has not been addressed. Using a collection of novel and established methods, we have developed a comprehensive, four‐component protocol for the validation of automatic deformable image registration systems over a range of IGRT applications. The protocol, which was applied to the Reveal‐MVS system, initially consists of a phantom study for determination of the system's general tendencies, while relative comparison of different registration settings is achieved through postregistration similarity measure evaluation. Synthetic transformations and contour‐based metrics are used for absolute verification of the system's intra‐modality and inter‐modality capabilities, respectively. Results suggest that the commercial system is more apt to account for global deformations than local variations when performing deformable image registration. Although the protocol was used to assess the capabilities of the Reveal‐MVS system, it can readily be applied to other commercial systems. The protocol is by no means static or definitive, and can be further expanded to investigate other potential deformable registration applications.

PACS numbers: 87.19.xj, 87.56.Da, 87.57.nj
Evaluation of tumor motion effects on dose distribution for hypofractionated intensity‐modulated radiotherapy of non‐small‐cell lung cancer
Authors: Kang Hyejoo , Yorke Ellen D. , Yang Jie , Chui Chen‐Shou , Rosenzweig Kenneth E. , Amols Howard I.
Published: February 2017

Respiration‐induced tumor motion during intensity‐modulated radiotherapy (IMRT) of non‐small‐cell lung cancer (NSCLC) could cause substantial differences between planned and delivered doses. While it has been shown that, for conventionally fractionated IMRT, motion effects average out over the course of many treatments, this might not be true for hypofractionated IMRT (IMHFRT). Numerical simulations were performed for nine NSCLC patients (11 tumors) to evaluate this problem. Dose distributions to the Clinical Target Volume (CTV) and Internal Target Volume (ITV) were retrospectively calculated using the previously‐calculated leaf motion files but with the addition of typical periodic motion (i.e. amplitude 0.36–1.26 cm, 3–8 sec period). A typical IMHFRT prescription of fractions was assumed. For the largest amplitude (1.26 cm), the average ± standard deviation of the ratio of simulated to planned mean dose, minimum dose, D95 and V95 were , , and for the CTV, and , , and for the ITV, respectively. There was minimal dependence on period or initial phase. For typical tumor geometries and respiratory amplitudes, changes in target coverage are minimal but can be significant for larger amplitudes, faster beam delivery, more highly‐modulated fields, and smaller field margins.

PACS number: 87.55.dk
Shielding assessment of a mobile electron accelerator for intra‐operative radiotherapy
Authors: Krechetov Alexandre S. , Goer Donald , Dikeman Kate , Daves Jodi L. , Mills Michael D.
Published: February 2017

The purpose of this investigation is to measure, characterize and report stray photon leakage and scatter radiation measurements from the Mobetron, an intra‐operative electron linear accelerator designed for use in an operating room environment. The study is needed due to recent changes to the shielding design of the Mobetron, and also to provide specific information that may be required by regulation in various jurisdictions. An analysis is performed on a number of manufactured units to determine an average 3D stray photon radiation map. This information provides a basis for determining patient‐based load restrictions and/or additional shielding for the operating room. The data presented evaluates the number of procedures for which the Mobetron may be safely operated in a typical unshielded operating room.

PACS number: 87.53.‐j; 87.56.‐v
Analysis of variation in calibration curves for Kodak XV radiographic film using model‐based parameters
Authors: Hsu Shu‐Hui , Kulasekere Ravi , Roberson Peter L.
Published: February 2017

Film calibration is time‐consuming work when dose accuracy is essential while working in a range of photon scatter environments. This study uses the single‐target single‐hit model of film response to fit the calibration curves as a function of calibration method, processor condition, field size and depth. Kodak XV film was irradiated perpendicular to the beam axis in a solid water phantom. Standard calibration films (one dose point per film) were irradiated at 90 cm source‐to‐surface distance (SSD) for various doses (16–128 cGy), depths (0.2, 0.5, 1.5, 5, 10 cm) and field sizes ( and ). The 8‐field calibration method (eight dose points per film) was used as a reference for each experiment, taken at 95 cm SSD and 5 cm depth. The delivered doses were measured using an Attix parallel plate chamber for improved accuracy of dose estimation in the buildup region. Three fitting methods with one to three dose points per calibration curve were investigated for the field sizes of and . The inter‐day variation of model parameters (background, saturation and slope) were 1.8%, 5.7%, and 7.7% (1 σ) using the 8‐field method. The saturation parameter ratio of standard to 8‐field curves was . The slope parameter ratio of standard to 8‐field curves ranged from 0.99 to 1.05, depending on field size and depth. The slope parameter ratio decreases with increasing depth below 0.5 cm for the three field sizes. It increases with increasing depths above 0.5 cm. A calibration curve with one to three dose points fitted with the model is possible with 2% accuracy in film dosimetry for various irradiation conditions. The proposed fitting methods may reduce workload while providing energy dependence correction in radiographic film dosimetry. This study is limited to radiographic XV film with a Lumisys scanner.

PACS number: 87.55.Qr
Three‐dimensional dosimetry of TomoTherapy by MRI‐based polymer gel technique
Authors: Watanabe Yoichi , Gopishankar N.
Published: February 2017

Verification of the dose calculation model and the software used for treatment planning is an important step for accurate radiation delivery in radiation therapy. Using BANG3 polymer gel dosimeter with a 3 Tesla magnetic resonance imaging (MRI) scanner, we examined the accuracy of TomoTherapy treatment planning and radiation delivery. We evaluated one prostate treatment case and found the calculated three‐dimensional (3D) dose distributions agree with the measured 3D dose distributions with an exception in the regions where the dose was much smaller (25% or less) than the maximum dose (2.5 Gy). The analysis using the gamma‐index (3% dose difference and 3 mm distance‐to‐agreement) for a volume of containing the planning target volume showed that the gamma values were smaller than unity for 53% of the voxels. Our measurement protocol and analysis tools can be easily applied to the evaluation of other newer complex radiation delivery techniques, such as intensity‐modulated arc therapy, with a reasonably low financial investment.

PACS numbers: 87.53Bn, 87.56Fc
A RapidArc planning strategy for prostate with simultaneous integrated boost
Authors: Jolly David , Alahakone Dineli , Meyer Juergen
Published: February 2017

Since the clinical implementation of novel rotational forms of intensity‐modulated radiotherapy, a variety of planning studies have been published that reinforce the major selling points of the technique. Namely, comparable or even improved dose distributions with a reduction in both monitor units and treatment times, when compared with static gantry intensity‐modulated radiotherapy. Although the data are promising, a rigorous approach to produce these plans has yet to be established. As a result, this study outlines a robust and streamlined planning strategy with a concentration on RapidArc class solutions for prostate with a simultaneous integrated boost. This planning strategy outlines the field setup, recommended starting objectives, required user interactions to be made throughout optimization and post‐optimization adjustments. A comparative planning study, with static gantry IMRT, is then presented as justification for the planning strategy itself. A variety of parameters are evaluated relating to both the planning itself (optimization and calculation time) and the plans that result. Results of this comparative study are in line with previously published data, and the planning process is streamlined to a point where the RapidArc optimization time takes minutes. Application of this planning strategy reduces the dependence of the produced plan on the experience of the planner, and has the potential to streamline the planning process within radiotherapy departments.

PACS numbers: 87.55.x, 87.55.D, 87.55.de, 87.55.dk
Breast phantom with silicone implant for evaluation in conventional mammography
Authors: Silva Fábio A. R. , Souza Luíza F , Salmon Carlos E. G. , Souza Divanizia N
Published: February 2017

With the increased incidence of cancer and a similarly increased number of surgeries for insertion of silicone breast implants, it is necessary to assess the effect of such material within the breast tissue, particularly in mammography, because of the reduction in the power of breast cancer diagnosis. In this work, we introduce a breast phantom with silicone implants in order to evaluate the influence of the implant on the visibility of the main mammographic findings: fibers, microcalcifications and tumor masses. In this proposed phantom, the breast tissue was simulated using gel paraffin. In the optical density of phantom mammograms with implants, a reduction in breast tissue visibility was seen corresponding to 23% when compared to a phantom without silicone implants. This poor visibility was due to the X‐ray beam scattering on silicone material; this effect produced a loss of visibility in the areas adjacent to the implant. It is expected that the proposed phantom model may be used as a device for the establishment of a technical standard for these types of procedures.

PACS number: 87.59 E