Effective Field Size Research Articles

OS-LFFD: a light and fast face detector with Ommateum structure

Face detection has been deployed on edge devices as the basis for face applications, but the devices cannot store large-scale models and have low computing power. The existing anchor-based face detection schemes cannot cover face images over a continuous size range, and their performance is not satisfactory. Obviously, good performances are accompanied by increased storage and lower speed. We find that the feature points in different layers correspond to a specific size range of RFs (receptive fields). According to the survey, the predictable range of RFs with the same size is the face on a continuous scale. Therefore, we argue that RFs are inherent anchors. A Light and Fast Face Detector with an Ommateum Structure (OS-LFFD) is proposed in this paper. By analyzing the correlation between the effective receptive field (ERF) and face sizes, a 4-branch network is designed to cover the objective range of face sizes. Each branch involves an ommateum block with a similar structure and shared parameters. It reduces the number of model parameters (8 M), which makes it much smaller than most face detectors. Experiments on the popular benchmarks WIDER FACE and FDDB using multiple hardware platforms demonstrate that the proposed scheme can considerably balance the accuracy and running speed.

Spatially-Adaptive Filter Units for Compact and Efficient Deep Neural Networks

Convolutional neural networks excel in a number of computer vision tasks. One of their most crucial architectural elements is the effective receptive field size, that has to be manually set to accommodate a specific task. Standard solutions involve large kernels, down/up-sampling and dilated convolutions. These require testing a variety of dilation and down/up-sampling factors and result in non-compact representations and excessive number of parameters. We address this issue by proposing a new convolution filter composed of displaced aggregation units (DAU). DAUs learn spatial displacements and adapt the receptive field sizes of individual convolution filters to a given problem, thus eliminating the need for hand-crafted modifications. DAUs provide a seamless substitution of convolutional filters in existing state-of-the-art architectures, which we demonstrate on AlexNet, ResNet50, ResNet101, DeepLab and SRN-DeblurNet. The benefits of this design are demonstrated on a variety of computer vision tasks and datasets, such as image classification (ILSVRC 2012), semantic segmentation (PASCAL VOC 2011, Cityscape) and blind image de-blurring (GOPRO). Results show that DAUs efficiently allocate parameters resulting in up to four times more compact networks at similar or better performance.

Multi-site evaluation of the Razor stereotactic diode for CyberKnife small field relative dosimetry

PurposeThe aims of this study were: (i) to validate in a multi-site context the suitability of the IBA Razor silicon diode detector for CyberKnife relative dosimetry. (ii) to fit the multi-center experimental data into a function relating the field output factors to the effective field size (EFS). Methods and materialsRatio of detector readings in clinical and reference field (OFdet) and beam profiles were acquired on five CyberKnife units for fixed collimator diameters (range 5–60 mm), using both Razor and PTW 60017 diodes. Measured OFdet were corrected using published MonteCarlo correction factors to get field output factors ΩQclin,Qmsrfclin,fmsr. Profiles were analyzed in terms of penumbra and EFS. ΩQclin,Qmsrfclin,fmsr obtained in four centers were fitted as a function of EFS, while the data of the 5th center were used to validate the fitting curve. ResultsDifferences between Razor and PTW60017 ΩQclin,Qmsrfclin,fmsr were within 1.5% over all centers down to 7.5 mm aperture and within 3.5% for the 5 mm diameter. The fit showed a coefficient of determination R2 = 0.997. The mean deviation of measured points from the predictive curve was within 0.5%. Data of the 5th center showed a mean deviation of 0.4% from the curve, with maximum differences within 2.5% for the 7.5 mm aperture. ConclusionsThe results confirmed the suitability of Razor detector for CyberKnife dosimetry by comparison to the PTW 60017 diode which has been well characterized and is in widespread use. The proposed mathematical relation between ΩQclin,Qmsrfclin,fmsr and EFS is a robust predictive model applicable to different CyberKnife systems and detectors.

Hardware-efficient color correlation–adaptive demosaicing with multifiltering

Color demosaicing is a key image processing step aiming to reconstruct the missing pixels from a recorded raw image that has a color filter array (CFA) pattern. The color correlation–based guided filters, such as minimized-Laplacian residual interpolation (MLRI), are known as the state-of-the-art demosaicing techniques. However, in the conventional guided filter-based techniques, the artifacts are generated in areas with low color correlation. Furthermore, a large number of line memories are required in the hardware implementation of a conventional guided filter-based technique because of the large effective field size. To overcome these two problems, we propose a color correlation–adaptive demosaicing algorithm that selectively applies a specific intracolor demosaicing to regions with low color correlation. We also propose an algorithm structure that reduces the effective field size in the vertical direction to reduce the number of line memories, while maintaining the image quality performance during the hardware implementation. The experimental results show that the proposed scheme can reduce the line memory to one-third while showing marginal performance degradation compared to the state-of-the-art MLRI weighted framework in terms of the color peak signal-to-noise ratio for the IMAX datasets.

P158] Analysis of different overlap of patched spot scanned proton fields

Purpose Proton treatment fields can be larger than the effective field size of the delivery machine. In this case, delivery is composed of multiple patched sub-fields, where the couch is moving between the patches. As our delivery machine uses parallel scanning, patched fields are currently delivered without overlap, but there is a possibility to change the overlap between patches to a defined distance to improve robustness. In this work we have evaluated the influence of different overlaps. Methods Measurements of patched fields with different amount of overlap have been performed with a CCD camera. 13 homogenous box fields of different sizes with and without preabsorber, have been measured with the CCD camera, each with 0 cm, 1 cm, 2 cm and 3 cm overlap. Offsets of ± 1 mm between the patches were introduced to evaluate the possible error of an unexpected movement between patches. The images have been analyzed using gamma analysis (1% local dose difference and 1 mm distance to agreement) as well as comparing profiles over the patched area. By comparing the different overlaps, each of them was ranked (from 1 to 4) for every set of samples. A rank of 1 was given to the overlap which had the best fit of measured data to the calculated data and a rank of 4 given to the sample with the worst fit. Results Smaller dose differences are seen with a pre-absorber in the field than without, and all results are consistent for different measurement depths. With offsets, the dose difference is smaller for greater overlaps. The ranking over all overlaps shows that the optimal overlap would be a 2 cm overlap (ranking score of 44), followed by a 3 cm overlap (45), 1 cm (59) and 0 cm (75). If measurements with offsets are excluded, the 2 cm overlap is still the best (22), whereas 1 cm (31) and 3 cm (31) overlaps are equally effective. Again the worst results were obtained with 0 cm overlap (36). Conclusions Based on the measurements taken for this project, the optimal overlap setting for patched fields is 2 cm.

Bi-layered/tri-layered bio-media in direct contact with metal diagonal horn for hyperthermia

AbstractIn this paper, theoretical/simulation study of specific absorption rate (SAR) and/or temperature distributions in a bi-layered bio-media (fat and muscle)/realistic tri-layered bio-media (skin, fat, and muscle layers) in direct contact with water-loaded metal diagonal horn (MDH) designed at 915 MHz are investigated. The effects of fat thickness on the input reflection coefficient, reflection coefficient at the interface between the MDH and the bi-layered bio-media, and the SAR distribution in the bi-layered bio-media are also studied through simulation and theoretically at 915 MHz. Further, the SAR parameters such as penetration depth and effective field size inside the bi-layered bio-media due to the MDH are evaluated theoretically and the theoretical results are compared with the corresponding simulation results. Finally, SAR and temperature distributions in tri-layered bio-media without and with embedded irregular/oval-shaped tumor are provided for demonstrating the hyperthermia performance of the MDH applicator.

Analysis of clinical data to determine the minimum number of sensors required for adequate skin temperature monitoring of superficial hyperthermia treatments

Purpose: Tumor response and treatment toxicity are related to minimum and maximum tissue temperatures during hyperthermia, respectively. Using a large set of clinical data, we analyzed the number of sensors required to adequately monitor skin temperature during superficial hyperthermia treatment of breast cancer patients.Methods: Hyperthermia treatments monitored with >60 stationary temperature sensors were selected from a database of patients with recurrent breast cancer treated with re-irradiation (23 × 2 Gy) and hyperthermia using single 434 MHz applicators (effective field size 351–396 cm2). Reduced temperature monitoring schemes involved randomly selected subsets of stationary skin sensors, and another subset simulating continuous thermal mapping of the skin. Temperature differences (ΔT) between subsets and complete sets of sensors were evaluated in terms of overall minimum (Tmin) and maximum (Tmax) temperature, as well as T90 and T10.Results: Eighty patients were included yielding a total of 400 hyperthermia sessions. Median ΔT was <0.01 °C for T90, its 95% confidence interval (95%CI) decreased to ≤0.5 °C when >50 sensors were used. Subsets of <10 sensors result in underestimation of Tmax up to −2.1 °C (ΔT 95%CI), which decreased to −0.5 °C when >50 sensors were used. Thermal profiles (8–21 probes) yielded a median ΔT < 0.01 °C for T90 and Tmax, with a 95%CI of −0.2 °C and 0.4 °C, respectively. The detection rate of Tmax ≥43 °C is ≥85% while using >50 stationary sensors or thermal profiles.Conclusions: Adequate coverage of the skin temperature distribution during superficial hyperthermia treatment requires the use of >50 stationary sensors per 400 cm2 applicator. Thermal mapping is a valid alternative.

Compact self-grounded Bow-Tie antenna design for an UWB phased-array hyperthermia applicator

Using UWB hyperthermia systems has the potential to improve the heat delivery to deep seated tumours. In this paper, we present a novel self-grounded Bow–Tie antenna design which is to serve as the basis element in a phased-array applicator. The UWB operation in the frequency range of 0.43–1 GHz is achieved by immersing the antenna in a water bolus. The radiation characteristics are improved by appropriate shaping the water bolus and by inclusion of dielectric layers on the top of the radiating arms of the antenna. In order to find the most appropriate design, we use a combination of performance indicators representing the most important attributes of the antenna. These are the UWB impedance matching, the transmission capability and the effective field size. The antenna was constructed and experimentally validated on muscle-like phantom. The measured reflection and transmission coefficients as well as radiation characteristics are in excellent agreement with the simulated results. MR image acquisitions with antenna located inside MR bore indicate a negligible distortion of the images by the antenna itself, which indicates MR compatibility.

Direct-Contact Water-Loaded Metal-Dielectric Wall Diagonal Horn Applicators for Hyperthermia

ABSTRACTThis paper describes simulation and/or experimental studies of specific absorption rate (SAR) and temperature distributions in a biological phantom (muscle)/realistic tri-layered bio-media without and with oval-/irregular-shaped tumour in direct contact with hybrid mode (water-loaded) metal-dielectric wall diagonal horn designed at 2450 and 915 MHz and their comparison among themselves with those due to respective conventional metal diagonal horns. The diagonal horns reported in this paper provide simple and effective means to enhance the penetration depth in the bio-medium/media. Moreover, effects on penetration depth and effective field size due to presence of oval- and irregular-shaped tumours in the tri-layered bio-media are also investigated at 915 MHz. It is demonstrated that desired temperature range 41 °C–45 °C can be achieved and maintained for 60 minutes with input power of 9 W at the frequency of 915 MHz for treating tumours at relatively greater depth.

Numerical investigation of novel microwave applicators based on zero-order mode resonance for hyperthermia treatment of cancer

This paper characterizes three novel microwave applicators based on zero-order mode resonators for use in hyperthermia treatment of cancer. The radiation patterns are studied with numerical simulations in muscle tissue-equivalent model at 434MHz. The relative performance of the applicators is compared in terms of reflection coefficient, current distribution, power deposition (SAR) pattern, effective field size in 2D and 3D tissue volumes, and penetration depth. One particular configuration generated the most uniform SAR pattern, with 25% SAR covering 84% of the treatment volume extending to 1cm depth under the aperture, while remaining above 58% coverage as deep as 3cm under the aperture. Recommendations are made to further optimize this structure.

Three-dimensional Numerical Simulation and Experimental Analysis of Austenite Grain Growth Behavior in Hot Forging Processes of 300M Steel Large Components

The microstructure models were integrated into finite element (FE) code, and a three-dimensional (3D) FE analysis on the entire hot forging processes of 300M steel large components was performed to predict the distributions of effective strain, temperature field and austenite grain size. The simulated results show that the finest grains distribute in the maximum effective strain region because large strain induces the occurrence of dynamic recrystallization. However, coarse macro-grains appear in the minimum effective strain region. Then, 300M steel forging test was performed to validate the results of FE simulation, and microstructure observations and quantitative analysis were implemented. The average relative difference between the calculated and experimental austenite grain size is 7.56%, implying that the present microstructure models are reasonable and can be used to analyze the hot forging processes of 300M steel.

Technical Note: Multicenter study of TrueBeam FFF beams with a new stereotactic diode: Can a common small field signal ratio curve be defined?

Small radiation fields (<30 mm) are typically involved in stereotactic body radiation therapy procedures. Output factor measurements are subjected to large uncertainties. The signal ratio (SR) readings, defined as the ratio of central axis reading, respectively, in the actual field size and in the reference field size, were evaluated in several centers and a common mathematical description of the SR curve was investigated. A couple of new unshielded stereotactic diodes (Razor, IBA) was tested under eight different TrueBeams using 10 MV flattering filter free beams with high dose rate (2400 MU/min). Small fields, ranging from 6 to 50 mm, were analyzed in terms of profiles and central axis point measurements. SRs were normalized to 30 mm field and were calculated as a function of nominal field size (NFS) and effective field size (EFS). From SRs acquired using Razor1 (four centers), a theoretical equation was extrapolated. Three centers with Razor2 were used to test the mathematical relationship. Finally, the two diodes were directly compared in the last center. The EFS was systematically smaller than NFS (p < 0.01) for all field size ranges, with mean difference of 0.9 ± 0.5 mm. The SR fits using the NFS and EFS had, respectively, R2 = 0.989 and R2 ≫ 0.999. The Razor2 centers' mean deviation from the predicted SRs, using the NFS and EFS fits, was, respectively, 3.4% and 0.5%. The maximum deviations were 5.0% (6 mm field size) for NFS and 1.9% for EFS. Maximum deviation of 0.5% between the two Razors was observed. EFS measurements were confirmed to be mandatory when comparing SRs over different centers. An equation establishing a functional relation between SRs and the EFS was obtained and tested for the new Razor diode.

Dosimetric characterization of linac small beams using a plastic scintillator detector: A multicenter study

Purpose In modern radiation therapy accurate dosimetry within small photon fields is a challenge. This study presents a multicenter characterization of MLC-defined small field for the two major linear accelerator manufacturers. Materials and methods The project enrolled 31 Italian centers, 15 equipped with Elekta Linacs and 16 equipped with Varian Linacs. Each center performed TPR, in-plane and cross-plane dose profile of 0.8 × 0.8 cm2 field and OFs measurements for field sizes ranging from 0.6 × 0.6 to 10 × 10 cm2. Set-up conditions were 10 cm depth in water phantom at SSD 90 cm. Measurements were performed using two Exradin W1 plastic scintillator detectors correcting for the Cerenkov effect as proposed by the manufacturer. Results Analysis of the measurements performed by 12 Varian and 13 Elekta centers was performed. TPR measurements showed standard deviations within 0.6%; penumbra values of dose profiles showed standard deviations within 0.5 mm. FWHM measurements showed a greater variability. OF measurements showed standard deviations within 1.5% for field size greater than 2 × 2 cm2; for field size less than 2 × 2 cm2 measurements’ variability increases with decreasing field size. OF values show no dependence from the effective field size. Conclusions Relatively high degree of consistency regarding TPR and penumbra values was registered. FWHM and OF instead show greater variability. Our work confirmed the importance of multicenter dosimetric studies and W1 PSD as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques.

Small field relative dosimetry using a silicon diode of new generation

Introduction Small field dosimetry is increasingly important due to the development of complex treatment techniques. Standard dosimetric procedures are mandatory to ensure the same treatment in each radiotherapy center. Purpose A multicentric study on small fields dosimetry for the major linear accelerator manufacturers, using two IBA unshielded silicon diode RAZOR in 30 different institutions in Italy is reported. Data were collected for each linac manufacturer and model with the main objective to provide indications to beginner institutions. Materials and methods In and cross-plane beam profiles and Relative Output ratios were measured for each field size at depth = 10 cm and at SSD = 90 cm. The long axis of the diode detector was placed parallel to the beam with the active volume positioned at the isocenter. The profiles were compared in terms of 80–20% penumbra. Output factors were calculated with respect to a jaw-collimated square field of 3 × 3 cm 2 and as a function of effective field size EOF. Results EOF of all linacs were in agreement within a few per mille from 5.6cm to 1cm FS. For FS below 1cm it is evident a different trend depending on different linac models. Data were fitted with a polynomial showing coefficients of determination R 2 > 0.98 . Penumbra measurements were in agreement each other for each FS and accelerator model. Conclusion Multicentric data have been collected with the same instrumentation and protocol setup, providing good accuracy in the measurements and allowing to create gold standard values to be used by those institutions who intend to implement new performing treatment techniques.

Small beam dosimetry: A multi-center multi-detector italian project

A project dedicated to stereotactic body radiotherapy (SBRT) dosimetric aspects started in the framework of the Italian Association of Medical Physics (AIFM) SBRT working group. Its main objectives are manifold but sharing the knowledge between different clinics is the one of the most important. More than 30 centres, equipped with Varian, Elekta, Siemens or CyberKnife linac were enrolled. The project was divided in several work-packages, the first one evaluated the relative measurements with detectors routinely used by individual centers and in the following different detectors run in various centre. Each centre in the same work-package performed dose profile of field size ranging from 0.6 × 0.6 cm2 to 5.0 × 5.0 cm2, and relative output factors (ROF) measurements with a diamond or silicon diode or scintillator detector. In workpackage-1 ROF values measured in the first phase were compared with the ones measured with a microdiamond showing a higher inter-center consistency with this dosimeter compared to routine detectors. In workpackage-2 a silicon diode of new generation was used also to develop a mathematical relation from multicentric experimental data, which describes and predicts the ROF as a function of effective field size for TrueBeam Varian and Elekta linacs. Workpackage-3 used a plastic scintillator for TPR20, 10 and ROF; the latter showed a greater variability. Workpackage-4 used diamond and plastic scintillator with Cyberknife beams, to evaluate if microDiamond could be a suitable alternative to silicon diodes for OF determination and to validate the feasibility of using the scintillator as a reference detector in consideration of the ČerenkovLightRatio and experimental uncertainties. The results of the study for all the detectors emphasized the usefulness of a multi-center validation over a single center approach. A project dedicated to stereotactic body radiotherapy (SBRT) dosimetric aspects started in the framework of the Italian Association of Medical Physics (AIFM) SBRT working group. Its main objectives are manifold but sharing the knowledge between different clinics is the one of the most important. More than 30 centres, equipped with Varian, Elekta, Siemens or CyberKnife linac were enrolled. The project was divided in several work-packages, the first one evaluated the relative measurements with detectors routinely used by individual centers and in the following different detectors run in various centre. Each centre in the same work-package performed dose profile of field size ranging from 0.6 × 0.6 cm2 to 5.0 × 5.0 cm2, and relative output factors (ROF) measurements with a diamond or silicon diode or scintillator detector. In workpackage-1 ROF values measured in the first phase were compared with the ones measured with a microdiamond showing a higher inter-center consistency with this dosimeter compared to routine detectors. In workpackage-2 a silicon diode of new generation was used also to develop a mathematical relation from multicentric experimental data, which describes and predicts the ROF as a function of effective field size for TrueBeam Varian and Elekta linacs. Workpackage-3 used a plastic scintillator for TPR20, 10 and ROF; the latter showed a greater variability. Workpackage-4 used diamond and plastic scintillator with Cyberknife beams, to evaluate if microDiamond could be a suitable alternative to silicon diodes for OF determination and to validate the feasibility of using the scintillator as a reference detector in consideration of the ČerenkovLightRatio and experimental uncertainties. The results of the study for all the detectors emphasized the usefulness of a multi-center validation over a single center approach.

Investigation on improved water-loaded diagonal horn applicators for hyperthermia

This paper describes simulation, theoretical, and/or experimental studies of specific absorption rate (SAR) distribution in biological phantom (muscle)/tri-layered bio-media without and with irregular-shaped tumors in direct contact with improved water-loaded metal diagonal horns designed at 2450 and 915 MHz. Further, thermal simulation results based on Pennes’ bio-heat equation are also provided for each of the proposed applicators, which is in direct contact with realistic tri-layered bio-media without and with irregular-shaped tumor embedded within the muscle layer. The proposed horns are improved versions of the respective conventional metal diagonal horns in which the aperture fields, which are modified by introducing four conducting pins at appropriate locations near each antenna aperture, correspond to fundamental and higher order modes. The theoretical aperture field distributions of the proposed horns designed at 2450 and 915 MHz are compared with the corresponding simulated ones. Further, the theoretical SAR parameters (penetration depth (PD) and effective field size (EFS)) in the phantom muscle medium due to the proposed horns designed at 2450 and 915 MHz are compared with the corresponding simulated and/or experimental results as well as with those obtained due to the corresponding conventional horns of identical dimensions. Moreover, effects on PD, EFS/EFS25, and temperature distribution profiles due to presence of irregular-shaped tumor in the tri-layered bio-media at 2450 and 915 MHz are also investigated. It is demonstrated that desired temperature range 41–45 °C can be achieved and maintained for 60 min with input power of 4/10 W at the frequencies of 2450/915 MHz for treating superficial tumors.

Conformal microstrip slot antenna with an AMC reflector for hyperthermia

This paper presents the simulation and experimental studies of a conformal microstrip slot antenna integrated with artificial magnetic conductor (AMC) for hyperthermia application. In the proposed applicator, an AMC consisting of an array of modified ring patches on a grounded dielectric substrate is located at optimized distance (=4 mm) from the microstrip slot antenna for improved performance of the applicator. The feed configuration of the proposed slot antenna consists of tapered microstrip line with curved tuning stub. The slot and feed configurations of the antenna are modified to widen its bandwidth so that changes in dielectric property of biological phantom medium can have minimal effect on its operating frequency and impedance bandwidth. In addition, the applicator with modified slot and feed arrangement provides enhanced heating depth in the phantom muscle medium. Provision for cooling of tissue surface is made by providing air gap between the slot antenna and phantom muscle medium. Moreover, the presence of AMC not only reduces the backfield but also enhances the penetration depth in the medium. Additionally, performance comparison of the proposed antenna–AMC and the antenna–perfect electric conductor(PEC) combinations in terms of input characteristics and specific absorption rate (SAR) parameters is also made. Finally, the effects of change in the radius of curvature of the substrate and bio-model on effective field size (EFS) for both homogeneous and tri-layered bio-models are also investigated. It is demonstrated through thermal simulation that temperature above 41 °C exists in the irregular-shaped tumor, which is embedded in the muscle region of the curved/planar tri-layered bio-model near its surface.

Infrared camera based thermometry for quality assurance of superficial hyperthermia applicators

The purpose of this work was to provide a feasible and easy to apply phantom-based quality assurance (QA) procedure for superficial hyperthermia (SHT) applicators by means of infrared (IR) thermography.The VarioCAM hr head (InfraTec, Dresden, Germany) was used to investigate the SA-812, the SA-510 and the SA-308 applicators (all: Pyrexar Medical, Salt Lake City, UT, USA). Probe referencing and thermal equilibrium procedures were applied to determine the emissivity of the muscle-equivalent agar phantom. Firstly, the disturbing potential of thermal conduction on the temperature distribution inside the phantom was analyzed through measurements after various heating times (5–50 min). Next, the influence of the temperature of the water bolus between the SA-812 applicator and the phantom’s surface was evaluated by varying its temperature. The results are presented in terms of characteristic values (extremal temperatures, percentiles and effective field sizes (EFS)) and temperature-area-histograms (TAH). Lastly, spiral antenna applicators were compared by the introduced characteristics.The emissivity of the used phantom was found to be ε = 0.91 ± 0.03, the results of both methods coincided. The influence of thermal conduction with regard to heating time was smaller than expected; the EFS of the SA-812 applicator had a size of (68.6 ± 6.7) cm2, averaged group variances were ±3.0 cm2. The TAHs show that the influence of the water bolus is mostly limited to depths of <3 cm, yet it can greatly enhance or reduce heat generation in this regime: at a depth of 1 cm, measured maximal temperature rises were 14.5 °C for TBolus = 30 °C and 8.6 °C for TBolus = 21 °C, respectively. The EFS was increased, too. The three spiral antenna applicators generated similar heat distributions.Generally, the procedure proved to yield informative insights into applicator characteristics, thus making the application of an IR camera a very useful tool in SHT technical QA.

Spheres, Rings, and Rods as Electrodes in Electrofishing: Their Effects on System Resistance and Electrical Fields

AbstractThree shapes of electrodes are used for most electrofishing: spheres, rings, and rods. The predictive value of theoretical equations and relative effects of electrode size, shape, and stock diameter (material thickness) on electrical characteristics have not been evaluated by designed experiment. I performed an experiment in a hatchery raceway, using minimum and maximum electrode size‐shape categories common in electrofishing: 15‐cm‐ and 30‐cm‐diameter spheres and rings and 48‐cm‐ and 96‐cm‐long rods (lengths equivalent to ring circumferences). Each size of ring and rod was fabricated in four stock diameters: 3, 6, 10, and 13 mm. Eighteen identical pairs of electrodes (two spheres, eight rings, eight rods) were energized with 120‐V, 60‐Hz sine‐wave AC. Observed values of system resistance (representing potential power demand), voltage gradient at 0–1 cm from an electrode surface (high‐hazard zone for fish), and distance to 0.1 V/cm (effective field size) were measured. Both size–shape and stock diameter had highly significant (P ≤ 0.01) effects on system resistance, high‐hazard zone, and effective field size. Size–shape effect was about nine times more important than stock diameter in its influence on system resistance; about six times more for effective field size; and about twice more for the high‐hazard zone. Boundary conditions imposed by the raceway limited the usefulness of theoretical equations; such boundaries would also exist in natural waters. Empirical measurements of circuits and fields are more accurate and realistic, than theoretical values, for application of electrode design. Lacking one's own empirical data, the data from this study may be used to test virtual electrofishing systems for electrode design. Scenarios are offered as examples for practical application of the results of this study.Received November 25, 2014; accepted October 13, 2015

METAMATERIAL ANTENNA ARRAYS FOR IMPROVED UNIFORMITY OF MICROWAVE HYPERTHERMIA TREATMENTS

2 Abstract |Current microwave hyperthermia applicators are not well suited for uniform heating of large tissue regions. The objective of this research is to identify an optimal microwave antenna array for clinical use in hyperthermia treatment of cancer. For this aim we present a novel 434 MHz applicator design based on a metamaterial zeroth order mode resonator, which is used to build larger array congurations. These applicators are designed to effectively heat large areas extending deep below the body surface and in this work they are characterized with numerical simulations in a homogenous muscle tissue model. Their performance is evaluated using three metrics: radiation pattern-based Effective Field Size (EFS), temperature distribution-bas Therapeutic Thermal Area (TTA), and Therapeutic Thermal Volume (TTV) reaching 41{45 ◦ C. For 2 � 2 and 2 � 3 array congurations, the EFS reaching > 25% of maximum SAR in the 3.5 cm deep plane is 100% and 91% of the array aperture area, respectively. The corresponding TTA for these arrays is 95% and 86%, respectively; and the TTV attaining > 41 ◦ C is over 85% of the aperture area to a depth of over 3 cm in muscle, using