Analysis and Design of Magnetic Shielding System for Breast Cancer Treatment with Hyperthermia Inductive Heating

An analysis and design of magnetic shielding system are presented for breast cancer treatment with hyperthermia inductive heating. It is a technique to control magnetic field intensity and relocate the heating area by using a rectangular shielding with aperture. The distribution of the lossy medium was analyzed using the finite difference time domain method. Theoretical analyses investigate whether a novel shielded system is effective for controlling the magnetic field distribution or heating position. Theoretical and experimental investigations were carried out using a lossy medium. The inductive applicator is a ferrite core with diameter of 7 cm, excited by 4 MHz signal and a maximum output power of 750 W. The results show that size of heating region can be controlled by varying the aperture size. Moreover, the investigation result revealed that the position of heating region can be relocated by changing the orientation of the ferrite core with shielded system in x-axis direction. The advantage of the magnetic shielding system is that it can be applied to prevent the side effects of hyperthermia cancer treatment by inductive heating

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 434 MHz. 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 1 cm depth under the aperture, while remaining above 58% coverage as deep as 3 cm under the aperture. Recommendations are made to further optimize this structure

Towards UWB microwave hyperthermia for brain cancer treatment

Despite numerous clinical trials demonstrating that microwave hyperthermia is a powerful adjuvant modality in the treatment of cancers, there have been few instances where this method has been applied to brain tumors. The reason is a combination of anatomical and physiological factors in this site that require an extra degree of accuracy and control in the thermal dose delivery which current systems are not able to provide. All clinical applicators available today are in fact based on a single-frequency technology. In terms of treatment planning options, the use of a single frequency is limiting as the size of the focal spot cannot be modified to accommodate the specific tumor volume and location. The introduction of UWB systems opens up an opportunity to overcome these limitations, as they convey the possibility to adapt the focal spot and to use multiple operating frequencies to reduce the power deposition in healthy tissues.In this thesis, we explore whether the current treatment planning methods can be meaningfully translated to the UWB setting and propose new solutions for UWB microwave hyperthermia. We analyze the most commonly used cost-functions for treatment planning optimization and discuss their suitability for use with UWB systems. Then, we propose a novel cost-function specifically tailored for UWB optimization (HCQ). To solve for the HCQ, we further describe a novel, time-reversal based, iterative scheme for the rapid and efficient optimization of UWB treatment plans. We show that the combined use of these techniques results in treatment plans that better exploit the benefits of UWB systems, yielding increased tumor coverage and lower peak temperatures outside the target. Next, we investigate the design possibilities of UWB applicators and introduce a fast E-field approximation scheme. The method can be used for the global optimization of the array parameters with respect to the multiple objectives and requirements of hyperthermia treatments. Together, the proposed solutions represent a step forward in the implementation of patient-specific hyperthermia treatments, increasing their accuracy and precision. The results suggest that UWB microwave hyperthermia for brain cancer treatment is feasible, and motivate the efforts for further development of UWB applicators and systems

Wide Band Embedded Slot Antennas for Biomedical, Harsh Environment, and Rescue Applications

For many designers, embedded antenna design is a very challenging task when designing embedded systems. Designing Antennas to given set of specifications is typically tailored to efficiently radiate the energy to free space with a certain radiation pattern and operating frequency range, but its design becomes even harder when embedded in multi-layer environment, being conformal to a surface, or matched to a wide range of loads (environments). In an effort to clarify the design process, we took a closer look at the key considerations for designing an embedded antenna. The design could be geared towards wireless/mobile platforms, wearable antennas, or body area network. Our group at UT has been involved in developing portable and embedded systems for multi-band operation for cell phones or laptops. The design of these antennas addressed single band/narrowband to multiband/wideband operation and provided over 7 bands within the cellular bands (850 MHz to 2 GHz). Typically the challenge is: many applications require ultra wide band operation, or operate at low frequency. Low frequency operation is very challenging if size is a constraint, and there is a need for demonstrating positive antenna gain

Ultra wideband microwave hyperthermia for brain cancer treatment

Despite numerous clinical trials demonstrating that microwave hyperthermia is a powerful adjuvant modality in the treatment of cancers, there have been few instances where this method has been applied to brain tumors. The reason is a combination of anatomical and physiological factors in this site that require an extra degree of accuracy and precision in the thermal dose delivery. Current clinical applicators are not able to provide such control, partly because they are designed to operate at a single fixed frequency. In terms of treatment planning, the use of a single frequency is limiting as the size of the focal spot cannot be modified to accommodate the specific tumor volume and location. The introduction of ultra wide-band (UWB) systems opens up an opportunity to overcome these limitations, as they convey the possibility of adapting the focal spot and obtaining different power deposition patterns to reduce the heating of healthy tissues.In this thesis, we explore whether the current SAR-based treatment planning methods can be meaningfully translated to the UWB setting and propose new solutions for deep UWB microwave hyperthermia. We analyze the most commonly used cost functions for treatment planning optimization and discuss their suitability for use with UWB systems. Then, we propose a novel SAR-based cost function (HCQ) for UWB optimization that exhibits a high correlation with the resulting tumor temperature. To solve for the HCQ, we describe a novel, time-reversal-based, iterative scheme for a rapid and efficient optimization of UWB treatment plans. Next, we investigate the design possibilities of UWB brain applicators and introduce a fast E-field approximation scheme to quickly explore a large number of array configurations. The method determines the best antenna arrangement around the head with respect to the multiple objectives and requirements of clinical hyperthermia. Together, the proposed solutions manage to achieve the level of tumor coverage and hot-spot suppression that is necessary for a successful treatment. Finally, we investigate the benefit of integrating hyperthermia delivered by an optimized UWB applicator into the radiation therapy plan for a pediatric medulloblastoma patient. The results suggest that UWB microwave hyperthermia for brain cancer treatment is feasible and motivate efforts for further development of UWB applicators and systems

Effect of practical layered dielectric loads on SAR patterns from dual concentric conductor microstrip antennas

Radiation patterns of 2 and 4cm square Dual Concentric Conductor (DCC) microstrip antennas were studied theoretically with Finite Difference Time Domain (FDTD) analysis and compared with experimental measurements of power deposition (SAR) in layered lossy dielectric loads. Single and array configurations were investigated with 915 MHz excitation applied across either one, two or four sides, or four corners of the square apertures. FDTD simulations were carried out for realistic models of a muscle tissue load coupled to the DCC antennas with a 5 mm thick bolus of either distilled water or low loss Silicone Oil. This study characterizes the effect on SAR of adding three additional thin dielectric layers which are necessary for clinical use of the applicator. These layers consist of a 0.1 mm thick dielectric coating on the array surface to provide electrical isolation of DCC apertures, and 0.15 mm thick plastic layers above and below the bolus to contain the liquid. Experimental measurements of SAR in a plane 1 cm deep in muscle phantom agree well with theoretical FDTD simulations in the multi-layered tissue models. These studies reveal significant changes in SAR for applicator configurations involving low dielectric constant (Er) layers on either side of a high Er water bolus layer. Prominent changes include a broadening and centring of the SAR under each aperture as well as increased SAR penetration in muscle. No significant differences are noted between the simple and complete load configurations for the low Er Silicone Oil bolus. Both theoretical and measured data demonstrate relatively uniform SAR distributions with50% of maximum SAR extending to the perimeter of single and multi-aperture array configurations of DCC applicators when using a thin 5 mm water or Silicone Oil bolus

On heating head and neck tumours using the novel clinical em applicator: the HYPERcollar

Abstract Purpose: Definition of all features and the potential of the novel HYPERcollar applicator system for hyperthermia treatments in the head and neck (H&N) region. Methods and Materials: The HYPERcollar applicator consists of 1) an antenna ring, 2) a waterbolus system and 3) a positioning system. The specific absorption rate (SAR) profile of this applicator is investigated by performing infra-red (IR) measurements in a cylindrical phantom. Mandatory patient-specific treatment planning is performed as an object lesson to a patient with a laryngeal tumour and an artificial lymph node metastasis. Results: The comfort tests with healthy volunteers have revealed that the applicator provides su±cient comfort to maintain in treatment position for an hour: in our center the standard hyperthermia treatment duration. We further established that a central focus in the neck can be obtained, with 50% iso-SAR lengths of 3.5cm in transversal directions and 9-11cm in the axial direction (z). Using treatment planning by detailed electromagnetic simulations, we showed that the SAR pattern can be optimized to enable simultaneous encompassing a primary laryngeal tumour and a lymph node metastasis at the 25% iso-SAR level. Conclusions: A site-specific H&N applicator was designed that enables good control and sufficient possibilities for optimizing the SAR pattern. In an ongoing clinical feasibility study we will investigate the possibilities of heating various target regions in the neck with this apparatus

Solving the time- and frequency-multiplexed problem of constrained radiofrequency induced hyperthermia

Targeted radiofrequency (RF) heating induced hyperthermia has a wide range of applications, ranging from adjunct anti-cancer treatment to localized release of drugs. Focal RF heating is usually approached using time-consuming nonconvex optimization procedures or approximations, which significantly hampers its application. To address this limitation, this work presents an algorithm that recasts the problem as a semidefinite program and quickly solves it to global optimality, even for very large (human voxel) models. The target region and a desired RF power deposition pattern as well as constraints can be freely defined on a voxel level, and the optimum application RF frequencies and time-multiplexed RF excitations are automatically determined. 2D and 3D example applications conducted for test objects containing pure water (r(target) = 19 mm, frequency range: 500–2000 MHz) and for human brain models including brain tumors of various size (r(1) = 20 mm, r(2) = 30 mm, frequency range 100–1000 MHz) and locations (center, off-center, disjoint) demonstrate the applicability and capabilities of the proposed approach. Due to its high performance, the algorithm can solve typical clinical problems in a few seconds, making the presented approach ideally suited for interactive hyperthermia treatment planning, thermal dose and safety management, and the design, rapid evaluation, and comparison of RF applicator configurations

An Investigation of Radiometer and Antenna Properties for Microwave Thermography

Microwave thermography obtains information about the subcutaneous body temperature by a spectral measurement of the intensity of the natural thermally generated radiation emitted by the body tissues. At lower microwave frequencies the thermal radiation can penetrate through biological tissue for significant distances. The microwave thermal radiation from inside the body can be detected and measured non-invasively at the skin surface by the microwave thermography technique, which uses a radiometer to measure the radiation which is received from an antenna on the skin. In the microwave region the radiative power received from a volume of material has a dependence on viewed tissue temperature T(r) of the form, where k is the Boltzmann's constant, B the measurement bandwidth, c(r) is the relative contribution from a volume element dv (the antenna weighting function). The weighting function, c(r), depends on the structure and the dielectric properties of the tissue being viewed, the measurement frequency and the characteristics of the antenna. In any practical radiometer system the body microwave thermal signal has to be measured along with a similar noise signal generated in the radiometer circuits. The work described in this thesis is intended to lead to improvement in the performance of microwave thermography equipment through investigations of antenna weighting functions and radiometer circuit noise sources. All work has been carried out at 3.2 GHz, the central operating frequency of the existing Glasgow developed microwave thermography system. The effects of input circuit losses on the operation of the form of Dicke radiometer used for the Glasgow equipment have been investigated using a computational model and compared with measurements made on test circuits. Very good agreement has been obtained for modelled and measured behaviour. The losses contributed by the microstrip circuit structure, that must be used in the radiometer at 3.2 GHz, have been investigated in detail. Microwave correlation radiometry, by "add and square" method, has been applied to the received signals from a crossed-pair antenna arrangement, the antennas being arranged to view a common region at a certain depth. The antenna response has been investigated using a noise source and by the nonresonant perturbation technique. The received pattern formed by the product of the individual antenna patterns gives a maximum depth in phantom dielectric material. The depth can be adjusted by changing the spacing of the antennas and the phase in an antenna path. However, the pattern is modulated by a set of positive and negative interference fringes so that the complete receive pattern has a complicated form. On uniform temperature distributions the total radiometric signal is zero with the positive and negative contributions cancelling each other out. The fringe modulation can be removed by placing the antennas close enough together, The pattern is then simple and gives a modest maximum response at a known depth in a known material. The radiometer system remains sensitive to the temperature gradients only and the wide range of dielectric properties and tissue structures in the region being investigated usually makes the system response difficult to interpret. For crossed-pair antennas in phase the effective penetration depth in high-and medium-water content tissues is about 2.5 cm at a frequency of 3.2 GHz. The field pattern observed was of the form expected from the measurements of the individual antenna behaviour with the appropriate interference pattern superimposed. The nonresonant perturbation technique has been developed and applied to assist the development of the medical application of both microwave thermographic temperature measurement and microwave hyperthermia induction. These techniques require the electromagnetic field patterns of the special antennas used to be known. These antennas are often formed by short lengths of rectangular or cylindrical waveguide loaded with a low-loss dielectric material to achieve good coupling to body tissues. The high microwave attenuation in biological materials requires the field configurations to be measured close to the antenna aperture in the near-field wave. The nonresonant perturbation is a simple technique which can be used to measure electromagnetic fields in lossy material close to the antenna. It has been applied here to measure accurately the antenna weighting function and the effective penetration depth in tissue simulating dielectric phantom materials. (Abstract shortened by ProQuest.)