Antenna Design, Radiobiological Modelling, and Non-invasive Monitoring for Microwave Hyperthermia

The death toll of cancers is on the rise worldwide and surviving patients suffer significant side effects from conventional therapies. To reduce the level of toxicity in patients treated with the conventional treatment modalities, hyperthermia (HT) has been investigated as an adjuvant modality and shown to be a potent tumor cell sensitizer for radio- and chemotherapy. During the past couple of decades, several clinical radiofrequency HT systems, aka applicators, have been developed to heat tumors. Systems based on radiative applicators are the most widely used within the hyperthermic community. They consist of a conformal antenna array and need a beamforming method in order to focus EM energy on the tumor through constructive interference while sparing the healthy tissue from excessive heating. Therefore, a hyperthermia treatment planning (HTP) stage is required before each patient\u27s first treatment session to optimize and control the EM power deposition as well as the resultant temperature distribution. Despite the vast amount of effort invested in HTP and the progress made in this regard during recent years, the clinical exploitation of HT is still hampered by technical limitations and patients can still experience discomfort during clinical trials. This, therefore, calls for a more efficient hardware design, better control of EM power deposition to minimize unwanted hotspots, and more accurate quantification and monitoring of the treatment outcome. Given these demands, the present report tries to address some of the above-mentioned challenges by proposing - A new antenna model customized for HT applications that surpasses previously proposed models from several points of view.- A hybrid beamforming method for faster convergence and a versatile, robust thermal solver for handling sophisticated scenarios.- A radiobiological model to quantify the outcome of a combined treatment modality of the Gamma Knife radiosurgery and HT.- A differential image reconstruction method to assess the feasibility of using the same system for both heating and microwave thermometry

On the Reconstruction Capability of the Linear Sampling Method

Linear Sampling Method (LSM), although a simple and fast qualitative method, encounters some limitations and restrictions when it comes to measurement set-up and realistic implementation. Addressing some difficulties arising from somewhat complicated measurement structures used to gather raw data for the reconstruction algorithm, this communication tries to show the effect of mutual coupling between antennas utilized in the measurement chamber. Another tangible effect of the antenna arrangement, covered here through reconstructing a reference scenario of Fresnel Institute dataset, has to do with the aspect-limited nature of scan lines. Reconstructions based on both simulated and measured data are reported

An adaptive finite element method for solving 3D electromagnetic volume integral equation with applications in microwave thermometry

An adaptive finite element method (AFEM) for the numerical solution of an electromagnetic volume integral equation (VIE) is presented. To solve the model VIE, the problem is formulated as an optimal control problem for minimization of Tikhonov\u27s regularization functional. A posteriori error estimates in the obtained finite element reconstruction and in the underlying Tikhonov\u27s functional are derived. Based on these estimates, adaptive finite element algorithms are formulated and numerically tested on the problem of microwave hyperthermia in cancer treatment. In this problem, the temperature change of a target in the computational domain results in the change of its dielectric properties. Numerical examples of monitoring this change show robust and qualitative three-dimensional reconstructions of the target using the proposed adaptive algorithms

An ultra-wideband compact design for hyperthermia: Open ridged-waveguide antenna

Antennas are the building block of radiative hyperthermia (HT) applicators. This study proposes a compact UWB antenna specifically tailored to meet the requirements for deep HT array applicators. The proposed Open Ridged-Waveguide (ORWG) antenna, which is an adaptation of a double-ridged horn antenna, operates over the frequency band of 400-800 MHz. It was experimentally assessed as a single element. The quality metrics considered were reflection coefficient, penetration depth, effective field size (EFS), and mutual coupling. The design shows a 75.5% fractional bandwidth with a reflection coefficient measured to be below -10 dB from 367 up to 820 MHz. The EFS is greater than the physical dimensions of the 3-by-4 cm aperture. The mutual coupling between two adjacent elements in the array, measured in a flat phantom arrangement, is lower than -30 dB throughout the entire band. The antenna\u27s performance was further tested in two deep HT scenarios in order to assess the mutual coupling and focussing abilities while in the array configuration. To this end, phased array applicators consisting of 10 and 16 ORWG antennas were simulated in CST, and the results are presented for a homogeneous cylindrical muscle phantom and a realistic patient model, respectively. The good agreement between the simulated and measured results suggests that the antenna can be successfully used for HT

Microwave thermometry with potential application in non-invasive monitoring of hyperthermia

Integration of an adaptive finite element method (AFEM) with a conventional least squares method has been presented. As a 3D full-wave forward solver, CST Microwave Studio has been used to model and extract both electric field distribution in the region of interest (ROI) and S-parameters of a circular array consisting of 16 monopole antennas. The data has then been fed into a differential inversion scheme to get a qualitative indicator of how the temperature distribution evolves over a course of the cooling process of a heated object. Different regularization techniques within the Tikhonov framework are also discussed, and a balancing principle for optimal choice of the regularization parameter was used to improve the image reconstruction quality of every 2D slice of the final image. Targets are successfully imaged via proposed numerical methods

A phased array applicator based on open ridged-waveguide antenna for microwave hyperthermia

Radiative hyperthermia is a clinically applied cancer treatment modality where antenna design is crucial to achieving therapeutic goals. Serving as the building block of a phased-array configuration, antennas are typically arranged in a cylindrical or elliptical array called applicator. This short communication proposes an elliptical phased array applicator based on a compact, UWB design from the category of double-ridged horn antennas customized for hyperthermia systems. The performance of the antenna, named open ridged-waveguide, has been experimentally assessed based on the quality metrics of the hyperthermic community. The proposed design achieves an ultra-wideband range of operation from 400 to 800 MHz with an aperture size of 3 by 4 cm. Moreover, thanks to the shielding provided by the metallic housing, the design proves good isolation better than -30 dB throughout the band. The power deposition capability of the proposed applicator followed by the thermal analysis is also investigated for a realistic headand neck patient model. The results indicate very good quality metrics achieved in the treatment planning of the patient

Radiobiological modeling of hyperthermia combined with Gamma-Knife radiosurgery in pediatric brain cancer

Assessment of the synergistic effect of radiotherapy (RT) and hyperthermia (HT) in clinical settings is crucial for further expansion of hyperthermia. The radiobiological modeling using an extended version of the LQ model with temperature-dependent radiosensitivity parameters has been suggested in combination with external beam radiotherapy in previous studies. This study investigates the radiobiological effect of intracranial hyperthermia combined with stereotactic radiosurgery (SRS) in pediatric brain cancers.\ua0The hyperthermia treatment plan was achieved with an elliptical applicator consisting of 16 ORWG antennas working at 400 MHz and a hybrid Specific Absorption Rate (SAR) optimization procedure based on Time-Reversal and PSO. The radiotherapy plan was created by the treatment planning software of Leksell Gamma Knife\uae Icon™

Radiobiological evaluation of combined gamma knife radiosurgery and hyperthermia for pediatric neuro-oncology

Combining radiotherapy (RT) with hyperthermia (HT) has been proven effective in the treatment of a wide range of tumours, but the combination of externally delivered, focused heat and stereotactic radiosurgery has never been investigated. We explore the potential of such treatment enhancement via radiobiological modelling, specifically via the linear-quadratic (LQ) model adapted to thermoradiotherapy through modulating the radiosensitivity of temperature-dependent parame-ters. We extend this well-established model by incorporating oxygenation effects. To illustrate the methodology, we present a clinically relevant application in pediatric oncology, which is novel in two ways. First, it deals with medulloblastoma, the most common malignant brain tumour in children, a type of brain tumour not previously reported in the literature of thermoradiotherapy studies. Second, it makes use of the Gamma Knife for the radiotherapy part, thereby being the first of its kind in this context. Quantitative metrics like the biologically effective dose (BED) and the tumour control probability (TCP) are used to assess the efficacy of the combined plan

Radiobiological Evaluation of Combined Gamma Knife Radiosurgery and Hyperthermia for Pediatric Neuro-Oncology

Combining radiotherapy (RT) with hyperthermia (HT) has been proven effective in the treatment of a wide range of tumours, but the combination of externally delivered, focused heat and stereotactic radiosurgery has never been investigated. We explore the potential of such treatment enhancement via radiobiological modelling, specifically via the linear-quadratic (LQ) model adapted to thermoradiotherapy through modulating the radiosensitivity of temperature-dependent parameters. We extend this well-established model by incorporating oxygenation effects. To illustrate the methodology, we present a clinically relevant application in pediatric oncology, which is novel in two ways. First, it deals with medulloblastoma, the most common malignant brain tumour in children, a type of brain tumour not previously reported in the literature of thermoradiotherapy studies. Second, it makes use of the Gamma Knife for the radiotherapy part, thereby being the first of its kind in this context. Quantitative metrics like the biologically effective dose (BED) and the tumour control probability (TCP) are used to assess the efficacy of the combined plan

The UWB phased array applicator: novel cooling solutions

Bolus plays a pivotal role in hyperthermia systems because it is not only a matching medium, but it can also help prevent unnecessary heating of the skin. In our work, the bolus is split into two parts, i.e. antenna water bolus (AWB) and the surface bolus (SB). The AWB is shaped for higher efficiency. However, this solution requires cooling of each individual antenna. For the surface bolus, a novel solution by means of hydrogel instead of typical plastic bags is proposed