Effect Of Field Size Research Articles

The angular dependence of a two dimensional monolithic detector array for dosimetry in small radiation fields

The purpose of this study is to investigate the directional dependence of a two dimensional monolithic detector array (M512) under 6 MV photon irradiation and to evaluate the effect of field size on angular dependence. Square fields of sizes: 3x3 cm2 and 10x10 cm2 were measured at the iso-centre of a cylindrical phantom. Beam angles with incidences from 00- 1800 in increments of 150 were used to investigate the central pixel angular response of M512, normalized to the pixel response for normal (0°) beam incidence. The angular response of the detector was compared to the response of EBT3 radiochromic film in the identical geometric orientation. The maximum angular dependence was observed at the angle 90°±15° to be -18.62% and -17.70% for the field sizes 3x3 cm2 and 10x10 cm2, respectively. The angular dependence of M512 showed no significant difference between field sizes of 3x3 cm2 and 10x10 cm2 (p>0.05). The maximum dose difference measured by the central pixel of M512 and EBT3 for all angles are -20% for 3x3 cm2 field size and -18.58% for the 10x10 cm2 field. The diode array’s size and packaging effects the angular response of the detector. The angular correction factor is necessary to apply to increase accuracy in dosimetry for arc treatment delivery.

Monte Carlo simulations of polycrystalline ferroelectrics: Effects of electric field and grain size on dynamic electric polarization

The present work incorporates a two dimensional Monte Carlo based polycrystalline simulation analysis for ferroelectric thin films. In the two stage process; first, grain growth is simulated via a traditional Q-State Monte Carlo method, taking into account isotropic grain boundary energies. Second, the grain growth results are incorporated within an electric polarization model, combining contributions from a three component Hamiltonian, including the electrostatic potential, nearest neighbor electrical interactions, and electrostatic energy. Among other findings, the results suggest a strong correlation between electric polarization and grain size, particularly at relatively large electric field frequencies.

Hofstadter butterfly in the Falicov–Kimball model on some finite 2D lattices

Spinless, interacting electrons on a finite size triangular lattice moving in an extremely strong perpendicular magnetic field are studied in comparison to a square lattice. Using a Falicov–Kimball model, the effects of Coulomb correlation, magnetic field and finite system size on their energy spectrum are observed. Exact diagonalization and Monte Carlo simulation methods (based on a modified Metropolis algorithm) have been employed to examine the recursive structure of the Hofstadter spectrum in the presence of several electronic correlation strengths for different system sizes. It is possible to introduce a gap in the density of states even in the absence of electron correlation, which is anticipated as a metal to insulator transition driven by an orbital magnetic field. With further inclusion of the interaction, the gap in the spectrum is modified and in some cases the correlation is found to suppress extra states manifested by the finite size effects. At a certain flux, the opened gap due to magnetic field is reduced by the Coulomb interaction. An orbital current is calculated for both the square and the triangular lattice with and without electron correlation. In the non-interacting limit, the bulk current shows several patterns, while the edge current shows oscillations with magnetic flux. The oscillations persist in the interacting limit for the square lattice, but not for the triangular lattice.

Optimisation of the design of pressurised irrigation systems for irregular shaped plots

A software tool has been developed to support decision-making in optimising the design of pressurised irrigation systems (sprinkler and drip irrigation) for agricultural fields with sub-plots of any shape or topography. The tool determines the design with minimum total water application cost (CT) (investment + operation). This study analysed the effect of field size, shape and slope on CT and emission uniformity (EU) for drip irrigation systems for almond and pepper, as well as two possible layouts for a maize crop for permanent sprinkler irrigation systems. The minimum CT design used polyethylene lateral pipes of 13.6 mm internal diameter at 250 kPa for drip irrigation and polyvinylchloride pipes of 46.4 mm internal diameter at 600 kPa for the permanent sprinkler irrigation systems, except in certain cases of where there were triangular plots. In the drip irrigation fields, which were more irregularly shaped and had the largest plots, the lowest CT was achieved with regulated flow emitters which in this study had an emission exponent x = 0.1. This was due to their increased efficiency and therefore decreases volume requirements. The use of pressure compensating drippers is recommended for large sub-plots (>1.5 ha in the analysed cases) with irregular shape and large slopes. Under the conditions studied, the 15 × 15-m layout had a slightly lower CT than the 18 × 18-m layout because it had greater uniformity and its increased irrigation efficiency reduced water consumption, despite having somewhat higher energy consumption and investment requirements than the 15 × 15-m layout.

A NOVEL, REMOVABLE, CERROBEND, BEAM-BLOCKING DEVICE FOR RADIATION THERAPY OF THE CANINE HEAD AND NECK: PILOT STUDY.

Radiation therapy of the head and neck can result in mucositis and other acute affects in the oral cavity. This prospective pilot study evaluated a novel, intraoral, beam-blocking device for use during imaging and therapeutic procedures. The beam-blocking device was made from a metal alloy inserted into a coated frozen dessert mold (Popsicle® Mold, Cost Plus World Market, Oakland, CA). The device was designed so that it could be inserted into an outer shell, which in turn allowed it to be placed or removed depending on the need due to beam configuration. A Farmer type ionization chamber and virtual water phantom were used to assess effects of field size on transmission. Six large breed cadaver dogs, donated by the owner after death, were recruited for the study. Delivered dose at the dorsal and ventral surfaces of the device, with and without the alloy block in place, were measured using radiochromic film. It was determined that transmission was field size dependent with larger field sizes leading to decreased attenuation of the beam, likely secondary to scatter. The mean and median transmission on the ventral surface without the beam-blocking device was 0.94 [range 0.94-0.96]. The mean and median transmission with the beam-blocking device was 0.52 [range 0.50-0.57]. The mean and median increase in dose due to backscatter on the dorsal surface of the beam-blocking device was 0.04 [range 0.02-0.04]. Findings indicated that this novel device can help attenuate radiation dose ventral to the block in dogs, with minimal backscatter.

Beam and tissue factors affecting Cherenkov image intensity for quantitative entrance and exit dosimetry on human tissue.

This study's goal was to determine how Cherenkov radiation emission observed in radiotherapy is affected by predictable factors expected in patient imaging. Factors such as tissue optical properties, radiation beam properties, thickness of tissues, entrance/exit geometry, curved surface effects, curvature and imaging angles were investigated through Monte Carlo simulations. The largest physical cause of variation of the correlation ratio between of Cherenkov emission and dose was the entrance/exit geometry (˜50%). The largest human tissue effect was from different optical properties (˜45%). Beyond these, clinical beam energy varies the correlation ratio significantly (˜20% for X-ray beams), followed by curved surfaces (˜15% for X-ray beams and ˜8% for electron beams), and finally, the effect of field size (˜5% for X-ray beams). Other investigated factors which caused variations less than 5% were tissue thicknesses and source to surface distance. The effect of non-Lambertian emission was negligible for imaging angles smaller than 60 degrees. The spectrum of Cherenkov emission tends to blue-shift along the curved surface. A simple normalization approach based on the reflectance image was experimentally validated by imaging a range of tissue phantoms, as a first order correction for different tissue optical properties.

Size-dependent snap-through and pull-in instabilities of initially curved pre-stressed electrostatic nano-bridges

This study investigates the electromechanical instabilities of micro/nanobeams with initial curved shape and subjected to electrostatic field and Casimir intermolecular force. Using modified couple stress theory and the principle of minimum potential energy and variational approach, the nonlinear equations associated with boundary conditions are derived. The generalized differential quadrature (GDQ) method is used to discretize the equations and boundary conditions, and then the discretized form of equations are solved numerically. In the end, the impacts of fringing field effect, beam imperfection and size effect on microbeam are investigated and the results are compared with experimental results. Besides, in the end the effect of Casimir intermolecular force in initially curved nanobeams and its symmetric and asymmetric effects on snap-through and pull-in instabilities are discussed.

SU‐G‐IeP4‐06: Feasibility of External Beam Treatment Field Verification Using Cherenkov Imaging

Purpose:Cherenkov light emission has been shown to correlate with ionizing radiation (IR) dose delivery in solid tissue. In order to properly correlate Cherenkov light images with real time dose delivery in a patient, we must account for geometric and intensity distortions arising from observation angle, as well as the effect of monitor units (MU) and field size on Cherenkov light emission. To test the feasibility of treatment field verification, we first focused on Cherenkov light emission efficiency based on MU and known field size (FS).Methods:Cherenkov light emission was captured using a PI‐MAX4 intensified charge coupled device(ICCD) system (Princeton Instruments), positioned at a fixed angle of 40° relative to the beam central axis. A Varian TrueBeam linear accelerator (linac) was operated at 6MV and 600MU/min to deliver an Anterior‐Posterior beam to a 5cm thick block phantom positioned at 100cm Source‐to‐Surface‐Distance(SSD). FS of 10×10, 5×5, and 2×2cm2 were used. Before beam delivery projected light field images were acquired, ensuring that geometric distortions were consistent when measuring Cherenkov field discrepancies. Cherenkov image acquisition was triggered by linac target current. 500 frames were acquired for each FS. Composite images were created through summation of frames and background subtraction. MU per image was calculated based on linac pulse delay of 2.8ms. Cherenkov and projected light FS were evaluated using ImageJ software.Results:Mean Cherenkov FS discrepancies compared to light field were <0.5cm for 5.6, 2.8, and 8.6 MU for 10×10, 5×5, and 2×2cm2 FS, respectably. Discrepancies were reduced with increasing field size and MU. We predict a minimum of 100 frames is needed for reliable confirmation of delivered FS.Conclusion:Current discrepancies in Cherenkov field sizes are within a usable range to confirm treatment delivery in standard and respiratory gated clinical scenarios at MU levels appropriate to standard MLC position segments

An electrochemical study of the nickel hydroxide-gold modified electrode employing the surface resistance technique

Simultaneous cyclic voltammetry (CV) and surface resistance (SR) measurements were employed to study the electrochemical behaviour of the nickel hydroxide-gold modified electrode. To this end, firstly, gold film electrodes of different thicknesses were synthesized, and their CV and SR responses within the potential regions corresponding to hydroxide ion adsorption (OHads) and gold oxide (AuO) formation in alkaline medium were analysed. Then, these gold film electrodes were modified with different nickel hydroxide surface coverages, and their CV and SR responses were compared with those of bare gold films within the same potential regions and electrolyte solution. While cyclic voltammetric responses of the bare gold film electrode and the nickel hydroxide-gold film modified electrode are practically the same within the whole potential range−0.5V<E<0.35V (SCE), SR responses are the same only within the potential range −0.3V<E<0.35V. Strong differences between the SR responses of the bare gold electrode and the nickel hydroxide-gold modified electrode within the potential range comprised between −0.5V and −0.3V are observed. SR data were interpreted in terms of the field effect and size effect theories formulated to study adsorption processes at thin metallic films. With regard to the bare gold film electrode, the field effect theory allows one to conclude that within the potential region corresponding to hydroxide ion adsorption, 77% of the electron density charge of gold is involved in the hydroxide ion–gold interaction. Besides, a linear relation between the surface resistance change (ΔR) and the degree of oxidation (θox) at fixed gold film thickness (ϕm) is obtained within the potential region corresponding to gold oxide formation. In agreement with the size effect theory, the ΔR/θox slope exhibits a linear dependence on ϕm−2. The same SR responses for the nickel hydroxide-gold modified electrode and the bare gold electrode within the potential range −0.3V<E<0.35V indicate that the nickel hydroxide layer does not directly interact with the gold film surface. However, after the reduction of OHads and AuO layers, at potential values more negative than −0.3V (SCE), an increase of the surface resistance is observed for the nickel hydroxide-gold modified electrode, which was attributed to nickel adatoms that directly interact with the gold film surface. On the basis of the electron conduction scattering model employed to describe the interaction of a metal film surface with a foreign atom layer, one can conclude that nickel film growth involves an initial stage in which nickel islands and then, compact structures are formed.

Implementation and evaluation of a transit dosimetry system for treatment verification

PurposeTo evaluate a formalism for transit dosimetry using a phantom study and prospectively evaluate the protocol on a patient population undergoing 3D conformal radiotherapy. MethodsAmorphous silicon EPIDs were calibrated for dose and used to acquire images of delivered fields. The measured EPID dose map was back-projected using the planning CT images to calculate dose at pre-specified points within the patient using commercially available software, EPIgray (DOSIsoft, France). This software compared computed back-projected dose with treatment planning system dose. A series of tests were performed on solid water phantoms (linearity, field size effects, off-axis effects). 37 patients were enrolled in the prospective study. ResultsThe EPID dose response was stable and linear with dose. For all tested field sizes the agreement was good between EPID-derived and treatment planning system dose in the central axis, with performance stability up to a measured depth of 18cm (agreement within −0.5% at 10cm depth on the central axis and within −1.4% at 2cm off-axis). 126 transit images were analysed of 37 3D-conformal patients. Patient results demonstrated the potential of EPIgray with 91% of all delivered fields achieved the initial set tolerance level of ΔD of 0±5-cGy or %ΔD of 0±5%. ConclusionsThe in vivo dose verification method was simple to implement, with very few commissioning measurements needed. The system required no extra dose to the patient, and importantly was able to detect patient position errors that impacted on dose delivery in two of cases.

Scatter radiation intensities around a clinical digital breast tomosynthesis unit and the impact on radiation shielding considerations.

To measure the scattered radiation intensity around a clinical digital breast tomosynthesis (DBT) unit and to provide updated data for radiation shielding design for DBT systems with tungsten-anode x-ray tubes. The continuous distribution of scattered x-rays from a clinical DBT system (Hologic Selenia Dimensions) was measured within an angular range of 0°-180° using a linear-array x-ray detector (X-Scan 0.8f3-512, Detection Technology, Inc., Finland), which was calibrated for the x-ray spectrum range of the DBT unit. The effects of x-ray field size, phantom size, and x-ray kVp/filter combination were investigated. Following a previously developed methodology by Simpkin, scatter fraction was determined for the DBT system as a function of angle around the phantom center. Detailed calculations of the scatter intensity from a DBT system were demonstrated using the measured scatter fraction data. For the 30 and 35 kVp acquisition, the scatter-to-primary-ratio and scatter fraction data closely matched with data previously measured by Simpkin. However, the measured data from this study demonstrated the nonisotropic distribution of the scattered radiation around a DBT system, with two strong peaks around 25° and 160°. The majority scatter radiation (>70%) originated from the imaging detector assembly, instead of the phantom. With a workload from a previous survey performed at MGH, the scatter air kerma at 1 m from the phantom center for wall/door is 1.76 × 10(-2) mGy patient(-1), for floor is 1.64 × 10(-1) mGy patient(-1), and for ceiling is 3.66 × 10(-2) mGy patient(-1). Comparing to previously measured data for mammographic systems, the scatter air kerma from Holgoic DBT is at least two times higher. The main reasons include the harder primary beam with higher workload (measured with total mAs/week), added tomosynthesis acquisition, and strong small angle forward scattering. Due to the highly conservative initial assumptions, the shielding recommendation from NCRP Report 147 is still sufficient for the Hologic DBT system given the workload from a previous survey at MGH. With the data provided from this study, accurate shielding calculation can be performed for Hologic DBT systems with specific workload and barrier distance.

Data and methods to assess occupational exposure to personnel involved in cardiac catheterization procedures

PurposeTo provide normalized scatter exposure data and methods for reliable estimation of cumulative effective dose and eye-lens equivalent dose to personnel involved in fluoroscopically guided cardiac catheterization (FGCC) procedures. MethodsAn anthropomorphic phantom was placed supine on the table of a modern digital C-arm angiographic system and 17 different fluoroscopic projections commonly employed during FGCC procedures were represented. Scatter exposure rates at the waist and eye level were measured for varying exposure parameters and position in the operating room. The effect of beam field size, patient size, use of radioprotective garments and small variations in projection angulation and table height on scatter radiation was investigated. ResultsApart from the position and use of radio-protective garments, radiation burden to operators during fluoroscopic guidance was found to remarkably depend beam field size (>45% reduction if a 10 × 10 cm2 instead of 15 × 15 cm2 fluoroscopy beam is used) and patient size (>25% increased scatter for obese patients). In contrast, the variation of measured scatter exposure from a given projection was found to be <10% when the source to skin distance was altered by ±10 cm or beam angulation of a specific projection was altered by ±10°. ConclusionPresented scatter exposure data charts and methods allow for prospective and retrospective estimation of effective dose and eye-lens equivalent dose to personnel involved in any FGCC procedure. Projection specific maps of scatter exposure produced may enhance familiarization of involved medical staff to good radiation protection practice and optimization of working habits in the cardiac catheterization lab.

A charged metal–organic framework for CO2/CH4 and CO2/N2 separation

A microporous metal–organic framework [InL][(CH3)2NH2]·(H4L=9-(3,5-dicarboxyphenyl)carbazole-3,6-dicarboxylic acid) (1) was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction and powder X-ray diffraction. The adsorption behavior of 1 has been investigated with respect to CO2, CH4 and N2, and the separation efficiency has been calculated by the Henry’s law analysis of isotherm data. The results indicated that the anionic framework with the inside protonated dimethylamine could enhance its selective adsorption performance for CO2 through strong adsorbent–adsorbate interaction aroused by a strong electrostatic field and pore size effect.

磁场和量子点尺寸对方形杂质量子点中电子性质的影响

磁场和量子点尺寸对方形杂质量子点中电子性质的影响

The effect of wind variability and domain size in the Persian Gulf on predicting nearshore wave energy near Doha, Qatar

Wind-wave generation and propagation processes in the Persian Gulf during October and November 2010 were simulated with a third-generation numerical wave model. Several different numerical configurations were used, with output at an instrument pier near the Doha, Qatar coast used to examine the efficacy of these approaches. Three wind sources were used: two sets of wind hindcasts which span the extent of the Gulf; and 15-min averaged winds measured at the pier and distributed as a spatially constant wind field for the model. Domain size, and its nearshore effect, was examined by using three domains of varying sizes and resolutions. Boundary conditions from nesting between larger and smaller domains were also varied to determine how incoming wave conditions from larger domains located further offshore can affect nearshore wave conditions. The effect of wind field, boundary conditions and domain size were quantified by examining the histograms, correlation coefficient, and root-means-square differences, of various parameters (significant wave height, wave height due to swells, peak period, and mean approach direction) for each wave condition at the site. It is determined that significant wave heights at the pier are strongly dependent on the wind fields used and also have some dependence on the use of boundary conditions, while nearshore peak periods are very dependent on the use of boundary conditions. Furthermore, the distribution of wave mean angles tends to be narrower for cases in which hindcast winds and boundary conditions were used. These results are consistent with the sporadic appearance of a strong, unidirectional wind field over the Persian Gulf basin.

A comparative study of the extent of cerebral microvascular injury following whole-brain irradiation versus reduced-field irradiation in long-term survivors of intracranial germ cell tumors

Background and purposeRadiation-induced cerebral cavernous malformation reflects post-irradiation impairment of cerebral microcirculation. Our purpose was to determine effects of radiation field size and dose on the extent of developing cavernous malformations in long-term survivors of intracranial germ cell tumors (GCTs). MethodsThe study involved 34 patients with a history of intracranial GCTs treated with either whole-brain or reduced-field irradiation and undergoing magnetic resonance (MR) imaging with a mean follow-up of 18.5years. The number of cavernous malformations on T2*-weighted MR images between whole-brain and reduced-field irradiation groups as well as between high- (50.2Gy) and low-dose (24.4Gy) fields were compared. ResultsA total of 235 cavernous malformation lesions were observed in 32 of 34 patients (94.1%). The mean number of lesions was 2.3 times as high in the whole-brain group as in the reduced-field group (P=0.00296). The number of lesions in high-dose fields was significantly larger than in low-dose (P<0.000001) or untreated fields (P<0.001). ConclusionRadiation field size and dose were positively associated with the number of cavernous malformations developed. Cavernous malformations detected on MR imaging can be used as a surrogate marker for microvascular injury following intracranial irradiation in long-term cancer survivors.

WE-AB-BRB-02: Development of a Micro-Sized Dosimeter for Real-Time Dose Monitoring and Small Field Dosimetry

Purpose: To investigate a miniature optical dosimeter for real-time, high-resolution dosimetry, and explore its potential applications for in vivo measurements and small field dosimetry. Methods: A micro-sized hemispherical (400 µm radius) scintillating detector was constructed from lanthanide activated phosphors doped with Europium (GOS:Eu) and encapsulated in a 17 gauge plastic catheter. A photon counting PMT and CCD-chip spectrometer were used to detect signals emitted from the detector. A single band-passing spectral approach (630nm) was implemented to discriminate the micro-phosphor optical signal from background signals (Cerenkov radiation) in the optical fiber. To test real-time monitoring capabilities, a 3D-printed phantom was used to detect an 192Ir HDR brachytherapy source at locations ranging from 1 to 4 cm radially and 12 cm along the travel axis of the HDR wire. To test the application of the micro-sized detector for small field dosimetry, the linearity of detector was characterized through irradiation of 6MV photon beam at dose-rates ranging from 100 to 600 MU, and the effect of field size was characterized through detections of beams ranging from 30×30 to 1×1 cm2 size. Results: With a 1 second integration time for the spectrometer, the recorded measurements indicated that the micro-sized detector allowed accurate detection of source position at distances of up to 6 cm along the axis of travel in water. EB measurements showed that the detected signal was linearly correlated with dose rate (R^2 = 0.99). The crossbeam profile was determined with a step size of ∼500 µm. Conclusion: Miniaturization of optical dosimeters is shown to be possible through the construction of lanthanide activated doped phosphors detectors. The small size of the detector makes it amenable to a variety of applications, including real-time dose delivery verification during HDR brachytherapy and EB beam calibrations in small fields.

SU-E-T-263: Development of Dose Monitor Unit Calculation Using Clarkson Integration for Proton Beam Therapy Using Beam-Wobbling System

Purpose: The purpose of the present study is to develop a calculation method of dose-calibration-factor using Clarkson integration for proton therapy employing the wobbling system and to evaluate accuracy of the calculation by comparison between calculations and measurements. Methods: CF and CALF stand for a dose-calibration-factor and a dose per monitor unit (MU), respectively. A measured dose-calibration-factor CFmeas is defined as a ratio of the measured dose per monitor unit in a patient-specific condition CALFpat to the measured dose per MU in a reference beam condition CALFref. The CFcalc is a product of three factors: CF1, CF2 and CF3. The CF1 and CF2 are a factor reflecting the effect of common beam delivery devices and that of patient specific devices and parameter (an aperture collimator, a range compensator and an air gap), respectively. The CF1 was obtained by interpolation using measured data. The CF2 was calculated using the Simplified Monte Carlo (SMC) method. The SMC method calculates a dose distribution by tracing individual protons and by using a measured Bragg curve in water. The CF3 representing the correction factor of field size effect was obtained by using the Clarkson integration. We compared the calculated and measured CF values for 20 prostate cases. Results: Field size correction was found to be important. The calculations reproduce the measurement results within an error of ±2.0%, except for a few cases. The error was about –3.1% for the small field area of less than19 square centimeters. Conclusion: We have developed a calculation method of dose-calibration-factor. Calculations agreed with measurements within ±2.0% for 90% of 20 prostate cases. Except for a small field size cases, the calculation method can be applied to determine the dose-calibration–factor for majority cases of prostate cancer.

Investigating in-field and out-of-field neutron contamination in high-energy medical linear accelerators based on the treatment factors of field size, depth, beam modifiers, and beam type

PurposeWe analysed the effects of field size, depth, beam modifier and beam type on the amount of in-field and out-of-field neutron contamination for medical linear accelerators (linacs). MethodsMeasurements were carried out for three high-energy medical linacs of Elekta Synergy Platform, Varian Clinac DHX High Performance and Philips SL25 using bubble detectors. The photo-neutron measurements were taken in the first two linacs with 18 MV nominal energy, whereas the electro-neutrons were measured in the three linacs with 9 MeV, 10 MeV, 15 MeV and 18 MeV. ResultsThe central neutron doses increased with larger field sizes as a dramatic drop off was observed in peripheral areas. Comparing with the jaws-shaped open-field of 10 × 10 cm, the motorised and physical wedges contributed to neutron contamination at central axis by 60% and 18%, respectively. The similar dose increment was observed in MLC-shaped fields. The contributions of MLCs were in the range of 55–59% and 19–22% in Elekta and Varian linacs comparing with 10 × 10 and 20 × 20 cm open fields shaped by the jaws, respectively. The neutron doses at shallow depths were found to be higher than the doses found at deeper regions. The electro-neutron dose at the 18 MeV energy was higher than the doses at the electron energies of 15 MeV and 9 MeV by a factor of 3 and 50, respectively. ConclusionThe photo- and electro-neutron dose should be taken into consideration in the radiation treatment with high photon and electron energies.

Optimising the attractiveness of winter oilseed rape fields as foraging habitat for the West Pannonian Great BustardOtis tardapopulation during winter

SummaryWinter oilseed rape represents an important food source for Great Bustards. Great Bustard surveys during four consecutive winters (2005/2006–2008/2009) were used to identify characteristics of oilseed rape fields, which increase their attractiveness for the species in its West Pannonian wintering area. The study was conducted in study areas in Eastern Austria, around the Austrian–Slovakian–Hungarian border and in the Hungarian Moson Plain. To test for effects of field size and isolation of fields from other rape fields, and the distance to the nearest paved road on occurrence and abundance of Great Bustards (maximum number of birds counted in individual rape fields per winter), we calculated generalized linear mixed models (GLMMs) including all three predictor variables as fixed effects and winter as random effect for each of the three study areas. Field size most strongly affected occurrence and abundance of Great Bustards. The availability of large (&gt;&gt;15 ha) winter rape fields far from paved roads is recommended as a prime conservation measure to improve the quality of rape fields as foraging habitat for Great Bustards during the winter months (November–March).