Kavitha Arunachalam

The performance of the genetic algorithm (GA) and particle swarm optimization (PSO) was compared to identify the best-suited algorithm for hyperthermia treatment planning (HTP) of breast cancer. Both algorithms were tested on four heterogeneous patient breast models derived from magnetic resonance (MR) images. Electromagnetic (EM) simulations indicate that PSO induces 5.7% less hotspot to target quotient (HTQ) compared to GA. However, coupled EM and thermal simulations of four patient models indicate that GA based HTP induces 1.25 °C - 3.87 °C higher average temperature in cancer tissue with limited thermal hotspots in healthy tissue when compared to PSO algorithm. This was observed to be due to the low power level assigned to each channel by PSO compared to GA. Coupled simulations of heterogeneous patient models indicate GA is a better global optimization algorithm for HTP of breast cancer.

In this work, we report a coaxial antenna consisting of a flexible Y-monopole with dual-band operation and low-profile wideband flexible ferrite choke for delivering localized HT treatment at shallow insertion depth of 50 mm inside the cervix using custom fabricated non-metallic intrauterine cervix tandem of 8 mm outer diameter and 1 mm wall thickness. Variable treatment coverage was achieved by selecting the excitation of the dual-band Y-monopole as 915 and 1300 MHz. The Y-monopole is a coaxial wire with a Y-split in the exposed inner conductor and wideband flexible ferrite sheet on the outer conductor to suppress the secondary current. The water loaded Y-monopole inside the intrauterine tandem cervix applicator with 15° bend angle resonated at 915 and 1300 MHz for arm lengths of 21 and 13.5 mm, respectively. The heating characteristics of Y-monopole was assessed using tissue-mimicking phantoms. Phantom measurements indicate dual band operation with power reflection coefficient $ \le - $24 dB at 915 and 1300 MHz. The measured extents of 25% axial specific absorption rate in tissue phantom at 915 and 1300 MHz is 39.4 and 28.4 mm, respectively. Localized power deposition with $\Delta T = 3 $ °C iso-contour of 46.3 mm × 39.2 mm and 37 mm × 31 mm along axial and radial directions was measured at 915 and 1300 MHz, respectively. Phantom measurements demonstrate the ability of the proposed antenna to deliver variable treatment volume to the cervix through 15° intrauterine tandem.

Targeted heating with minimal dose to neighboring tissues is possible with intra cavitary microwave applicators as they can treat tumors within/or nearby body cavities. Here we present an intra cavitary applicator for hyperthermia treatment of gynecological cancers at 434 MHz. A 3D numerical model of the applicator with conformal patch antenna in muscle tissue is studied for rectangular patch, variations of bow tie and spiral antennas. Antenna performance is evaluated in terms of size, return loss, bandwidth, specific absorption rate (SAR) and effective field surface (EFS). Fish tailed bow tie and spiral patches exhibited ≤-25 dB return loss and ≥25 MHz bandwidth compared to other shapes. EFS of spiral antenna is larger than fish tail. However, ratio of EFS to patch area indicates larger volumetric power deposition for fish tailed bow tie. From simulation results, it can be concluded that an array of fish tailed bow tie and/or spiral patch antennas would provide adjustable heating profile with high power deposition.

The aim of this study was to describe the design and characterisation of a miniaturised 434 MHz patch antenna enclosed in a metal cavity for microwave hyperthermia treatment of cancer. Materials and methods: Electromagnetic (EM) field distribution in the near field of a microstrip patch irradiating body tissue was studied using finite element method (FEM) simulations. Antenna miniaturisation was achieved through dielectric loading with very high permittivity, metal enclosure, patch folding and shorting post. Frequency dependent electrical properties of materials were incorporated wherever appropriate using dispersion model and measurements. Antenna return loss and specific absorption rate (SAR) at 434 MHz were measured on muscle phantoms for characterisation. Results: The design was progressively optimised to yield a compact 434 MHz patch (22 mm × 8.8 mm × 10 mm) inside a metal cavity (40 mm × 12 mm) with integrated coupling water bolus (35 mm). The fabricated antenna with integrated water bolus was self resonant at 434 MHz without load, and has better than-10 dB return loss (S11) with 13-20 MHz bandwidth on two different phantoms. SAR at 434 MHz measured using an infrared (IR) thermal camera on split phantoms indicated penetration depth for-3 dB SAR as 8.25 mm compared to 8.87 mm for simulation. The simulated and measured SAR coverage along phantom depth was 3.09 cm2 and 3.21 cm2 respectively at-3 dB, and 6.42 cm2 and 9.07 cm2 respectively at-6 dB. SAR full width at half maximum (FWHM) at 5 mm and 20 mm depths were 54.68 mm and 51.18 mm respectively in simulation, and 49.47 mm and 43.75 mm respectively in experiments. Performance comparison of the cavity-backed patch indicates more than 89% co-polarisation and higher directivity which resulted in deeper penetration compared to the patch applicators of similar or larger size proposed for hyperthermia treatment of cancer. Conclusion: The fabricated cavity-backed applicator is self-resonant at 434 MHz with a negligible shift in resonance when coupled to different phantoms, Δf/f0 less than 1.16%. IR thermography-based SAR measurements indicated that the-3 dB SAR of the cavity-backed aperture antenna covered the radiating aperture surface at 5 mm and 20 mm depths. It can be concluded that the compact cavity-backed patch antenna has stable resonance, higher directivity and low cross polarisation, and is suitable for design of microwave hyperthermia array applicators with adjustable heating pattern for superficial and/or deep tissue heating.

Hyperthermia as an adjuvant to chemotherapy and radiation therapy is a promising treatment modality for deep seated breast tumors where phased array antennas positioned around the breast are used to steer the power inside the tumor. In this work, we present semi-ellipsoidal and conical shaped phased array (PA) applicators for targeted hyperthermia treatment of locally advanced breast cancer. Both PA configurations have 18 patch antennas arranged in three rings operating at 434 MHz. Electromagnetic simulations of the two PA configurations are presented for a layered three-dimensional breast model to assess their ability to deliver targeted power. Preliminary results suggest better power deposition characteristics for the conical PA applicator.

Targeted hyperthermia treatment administered as an adjuvant to radiotherapy requires heterogeneous 3D patient model for treatment planning. Treatment planning is crucial for targeted delivery of hyperthermia treatment to the tumor target while sparing the surrounding healthy organs. Computed tomography (CT) data of the patient has poor soft-tissue contrast. As a result, automating patient image segmentation for 3D model generation is a time-consuming semi-automated process. Automated patient model generation is an amalgamation of technology and medical expertise in radiology. In this work, we present our preliminary results on machine learning approach for automated generation of 3D patient models for hyperthermia treatment planning using patient CT data of cervical cancer patients.

Genetic algorithm-based array thinning technique is investigated in this paper to study the performance of our 18-element 434 MHz phased array breast applicator when driven by reduced number of active antennas. Selective power deposition ability was assessed for 18, 15, 12, and 9 active antennas on 25 patient models with varying characteristics. The average hotspot to target quotient of 18-, 15-, 12-, and 9-antenna excitation in 25 patient models was 1.18, 1.09, 1.09, and 1.13, respectively. The average temperature in 50% tumor volume for 18-, 15-, 12-, and 9-antenna excitation was 42.42 °C, 42.48 °C, 42.49 °C, and 42.48 °C, respectively. The temperature induced in tumor and healthy tissues is similar for varying number of active channels. However, the amount of power consumed was 25.2%, 53.9%, 97.9% higher for 15, 12, 9 active antennas compared to the filled array. Antenna array with 12 active elements was chosen as the optimal combination as it provided selective tumor heating with good tradeoff between number of channels and power consumption. The heating ability of the thinned array was assessed for 50% reduction in the number of active antennas on patient derived heterogeneous breast phantoms for five tumor target locations. The good agreement between simulated and measured thermal distributions demonstrate the selective heating ability of our phased array applicator for 50% reduction in hardware resources. The study outcome enables us to realize a cost-effective hyperthermia treatment delivery system.

This paper presents a compact water-loaded coaxial balun configurations for targeted heat delivery for intracavitary hyperthermia treatment of cancer. Balun configurations of choke were analyzed using a 3\lambda/8 monopole at 915 MHz. The surface current density and volume loss density characteristics were used to evaluate balun efficiency and were compared with a conventional monopole without balun. The antenna performance with and without the balun configurations was numerically assessed and compared in terms of specific absorption rate (SAR) and input power reflection coefficient. The numerical designs were experimentally validated in muscle mimicking liquid phantoms.

Cancers of the neck, breast, and lower extremities are common malignancies diagnosed in India with a higher incidence of advanced-stage disease. Phased array (PA) applicators reported for hyperthermia treatment (HT) of the breast have small focal region and high cross-coupling, and those reported for lower extremities provide regional heating and limited steering. In this study, we present the numerical design of site-specific PA applicators for HT of large solid tumors in the neck, breast, and lower extremities using a miniaturized 434 MHz cavity-backed water-loaded patch antenna. The fabricated antenna has 38 × 36 mm2 aperture, more than 90% power coupling, 25 MHz bandwidth, and good agreement between simulated and measured specific absorption rate (SAR) in phantom. The site-specific applicators demonstrated less power reflection (<−17.9 dB) and cross-coupling (<−26.8 dB) for 5 mm inter-ring spacing. SAR indicators for 64 cc tumor at varying locations in simplified layered three-dimensional (3D) tissue models of the neck, breast, and leg showed average power absorption ratio (aPAratio) ≥ 3.16, target to hotspot quotient (THQ) ≥ 0.57, 25% iso-SAR coverage (TC25) ≥ 81%, and 50% iso-SAR coverage (TC50) ≥51.8%. Simulation results of site-specific applicators for 3D inhomogeneous patient models showed aPAratio ≥ 5.98, THQ ≥ 0.9, TC50 ≥ 86%, and 100% TC25 for all sites. It is concluded that the 434 MHz miniaturized cavity-backed patch antenna can be used to develop high-density PA applicators with 12–24 antennas for HT of large solid tumors (≥4 cm) in the neck, breast, and lower extremities with 3D steering ability and less cross-coupling (≤−26.8 dB). © 2020 Bioelectromagnetics Society.

Hyperthermia treatment of locally advanced mouth and oral cancers requires three-dimensional model of the patient, mostly emphasizing nasal throat region for treatment planning. 3D patient-specific model is crucial to plan the procedure for effective and localized thermal therapy. An image-based reconstruction technique, structure from motion (SfM) is a cost effective, flexible and efficient solution for this end application. Although SfM provides various algorithms and pipelines, it is important to select the optimum image capturing technique and effective pipeline to obtain robust 3D image reconstruction. In this work, we present the evaluation and analysis of effective hand-held image capturing techniques and performance of few open-source reconstruction pipelines tested on custom synthetic and real world captured data.