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

Utility of Microwave Radiometry for Diagnostic and Therapeutic Applications of Non-Invasive Temperature Monitoring

This paper describes the use of microwave radiometry for several diagnostic and therapeutic applications that can benefit from accurate non-invasive measurement of volume average temperature of tissue regions extending 4cm or more into the body. Design features are summarized for an appropriate high sensitivity long term stable system with 2.5 and 7 cm diameter receive antennas and integral 1.35 GHz total power radiometer electronics. Radiometer performance is characterized with electromagnetic and thermal simulations and experimental measurements in realistic models of two typical clinical applications. Results demonstrate sufficient sensitivity to track clinically significant changes in temperature of deep tissue targets for applications like the non-invasive detection of vesicoureteral reflux and monitoring brain “core” temperature during extended hypothermic surgery

Dielectric properties measurements of brown and white adipose tissue in rats from 0.5 to 10 GHz

Brown adipose tissue (BAT) plays an important role in whole body metabolism and with appropriate stimulus could potentially mediate weight gain and insulin sensitivity. Although imaging techniques are available to detect subsurface BAT, there are currently no viable methods for continuous acquisition of BAT energy expenditure. Microwave (MW) radiometry is an emerging technology that allows the quantification of tissue temperature variations at depths of several centimeters. Such temperature differentials may be correlated with variations in metabolic rate, thus providing a quantitative approach to monitor BAT metabolism. In order to optimize MW radiometry, numerical and experimental phantoms with accurate dielectric properties are required to develop and calibrate radiometric sensors. Thus, we present for the first time, the characterization of relative permittivity and electrical conductivity of brown (BAT) and white (WAT) adipose tissues in rats across the MW range 0.5-10GHz. Measurements were carried out in situ and post mortem in six female rats of approximately 200g. A Cole-Cole model was used to fit the experimental data into a parametric model that describes the variation of dielectric properties as a function of frequency. Measurements confirm that the dielectric properties of BAT (εr = 14.0-19.4, σ = 0.3-3.3S/m) are significantly higher than those of WAT (εr = 9.1-11.9, σ = 0.1-1.9S/m), in accordance with the higher water content of BAT

Focused ultrasound for treatment of bone tumours.

PURPOSE: Focused ultrasound (FUS) is a modality with rapidly expanding applications across the field of medicine. Treatment of bone lesions with FUS including both benign and malignant tumours has been an active area of investigation. Recently, as a result of a successful phase III trial, magnetic resonance-guided FUS is now a standardised option for treatment of painful bone metastases. This report reviews the clinical applications amenable to treatment with FUS and provides background on FUS and image guidance techniques, results of clinical studies, and future directions. METHODS: A comprehensive literature search and review of abstracts presented at the recently completed fourth International Focused Ultrasound Symposium was performed. Case reports and older publications revisited in more recent studies were excluded. For clinical studies that extend beyond bone tumours, only the data regarding bone tumours are presented. RESULTS: Fifteen studies assessing the use of focused ultrasound in treatment of primary benign bone tumours, primary malignant tumours, and metastatic tumours meeting the search criteria were identified. For these clinical studies the responders group varied within 91-100%, 85-87% and 64-94%, respectively. Major complications were reported in the ranges 0%, 0-28% and 0-4% for primary benign, malignant and metastatic tumours, respectively. CONCLUSIONS: Image-guided FUS is both safe and effective in the treatment of primary and secondary tumours. Additional phase III trials are warranted to more fully define the role of FUS in treatment of both benign and malignant bone tumours

Tumor bed brachytherapy for locally advanced laryngeal cancer: a feasibility assessment of combination with ferromagnetic hyperthermia

Purpose. To assess the feasibility of adding hyperthermia to an original method of organ-preserving brachytherapy treatment for locally advanced head and neck tumors. Methods and materials. The method involves organ-preserving tumor resection and adjunctive high-dose-rate (HDR) brachytherapy delivered via afterloading catheters. These catheters are embedded in a polymeric implant prepared intraoperatively to fill the resection cavity, allowing precise computer planning of dose distribution in the surrounding at-risk tumor bed tissue. Theoretical and experimental analyzes address the feasibility of heating the tumor bed implant by coupling energy from a 100 kHz magnetic field applied externally into ferromagnetic particles, which are uniformly distributed within the implant. The goal is to combine adjuvant hyperthermia (40 °C–45 °C) to at-risk tissue within 5 mm of the resection cavity for thermal enhancement of radiation and chemotherapy response. Results. A five-year relapse free survival rate of 95.8% was obtained for a select group of 48 male patients with T3N0M0 larynx tumors, when combining organ-preserving surgery with HDR brachytherapy from a tumor bed implant. Anticipating the need for additional treatment in patients with more advanced disease, a theoretical analysis demonstrates the ability to heat at-risk tissue up to 10 mm from the surface of an implant filled with magnetically coupled ferromagnetic balls. Using a laboratory induction heating system, it takes just over 2 min to increase the target tissue temperature by 10 °C using a 19% volume fraction of ferromagnetic spheres in a 2 cm diameter silicone implant. Conclusion. The promising clinical results of a 48 patient pilot study demonstrate the feasibility of a new organ sparing treatment for laryngeal cancer. Anticipating the need for additional therapy, theoretical estimations of potential implant heating are confirmed with laboratory experiments, preparing the way for future implementation of a thermobrachytherapy implant approach for organ-sparing treatment of locally advanced laryngeal cancer

Recent technological advancements in radiofrequency- andmicrowave-mediated hyperthermia for enhancing drug delivery

Hyperthermia therapy is a potent enhancer of chemotherapy and radiotherapy. In particular, microwave (MW) and radiofrequency (RF) hyperthermia devices provide a variety of heating approaches that can treat most cancers regardless the size. This review introduces the physics of MW/RF hyperthermia, the current state-of-the-art systems for both localized and regional heating, and recent advancements in hyperthermia treatment guidance using real-time computational simulations and magnetic resonance thermometry. Clinical trials involving RF/MW hyperthermia as adjuvant for chemotherapy are also presented per anatomical site. These studies favor the use of adjuvant hyperthermia since it significantly improves curative and palliative clinical outcomes. The main challenge of hyperthermia is the distribution of state-of-the-art heating systems. Nevertheless, we anticipate that recent technology advances will expand the use of hyperthermia to chemotherapy centers for enhanced drug delivery. These new technologies hold great promise not only for (image-guided) perfusion modulation and sensitization for cytotoxic drugs, but also for local delivery of various compounds using thermosensitive liposomes

Optimization of Chest Wall Hyperthermia Treatment Using a Virtual Human Chest Model

This work explores different coupling configurations (direct contact, air and water coupling) between a single 915 MHz waveguide applicator and human tissue in the setting of chest wall recurrence (CWR) of breast cancer. The objective is to treat chest wall tumours with microwave hyperthermia, while avoiding hot spots in critical areas such as scars and ribs. The best coupling configuration was a customized 24×29 cm water bolus developed by our team. It helps the applicator deliver an effective field size of 268 cm2 at 1 cm depth and a penetration depth of 2-3 cm. Water bolus thickness can be adjusted during treatment (0.5-4 cm) to shift hot spot locations and thus homogenize thermal dose delivered over a 60 min hyperthermia treatment. The virtual human chest model is easily customized so it can be used as a tool for treatment planning and quality assurance testing of microwave applicator configurations

ESHO benchmarks for computational modeling and optimization in hyperthermia therapy

Background: The success of cancer hyperthermia (HT) treatments is strongly dependent on the temperatures achieved in the tumor and healthy tissues as it correlates with treatment efficacy and safety, respectively. Hyperthermia treatment planning (HTP) simulations have become pivotal for treatment optimization due to the possibility for pretreatment planning, optimization and decision making, as well as real-time treatment guidance. Materials and methods: The same computational methods deployed in HTP are also used for in silico studies. These are of great relevance for the development of new HT devices and treatment approaches. To aid this work, 3 D patient models have been recently developed and made available for the HT community. Unfortunately, there is no consensus regarding tissue properties, simulation settings, and benchmark applicators, which significantly influence the clinical relevance of computational outcomes. Results and discussion: Herein, we propose a comprehensive set of applicator benchmarks, efficacy and safety optimization algorithms, simulation settings and clinical parameters, to establish benchmarks for method comparison and code verification, to provide guidance, and in view of the 2021 ESHO Grand Challenge (Details on the ESHO grand challenge on HTP will be provided at https://www.esho.info/). Conclusion: We aim to establish guidelines to promote standardization within the hyperthermia community such that novel approaches can quickly prove their benefit as quickly as possible in clinically relevant simulation scenarios. This paper is primarily focused on radiofrequency and microwave hyperthermia but, since 3 D simulation studies on heating with ultrasound are now a reality, guidance as well as a benchmark for ultrasound-based hyperthermia are also included

A Novel Compact Microwave Radiometric Sensor to Noninvasively Track Deep Tissue Thermal Profiles

Drawing from space technology to measure star temperature, we developed a noninvasive sensor to passively track thermal profiles in tissues well below the skin (\u3e5cm). Ultra-low noise amplifiers combined with ultralow-loss switches in the 1- 2GHz band produce a high sensitivity multiband microwave radiometer. Due to the complex multilayer anatomy of human head, multiple sensing bands are needed to reconstruct the temperature of deep brain tissue. This is achieved by using a digitally controlled filter bank. To study its accuracy, the sensor was calibrated and tested in a multilayer phantom model of the human head with differential scalp and brain temperatures. Results of phantom testing showed that calculated radiometric equivalent brain temperature agreed within 0.4°C of measured temperature when circulating homogenized brain phantom was lowered 10°C and returned to original temperature (37°C), while scalp was maintained constant over a 4.6-hour experiment. Feasibility of clinical monitoring was assessed in a pediatric patient during a hypothermic heart surgery. Over the 2-hour surgery, the radiometric sensor tracked within 1°C of rectal and nasopharynx temperatures, except during rapid cooldown and heatup periods when brain temperature deviated 2-4°C from slower responding core temperature surrogates. In summary, the sensor demonstrated long term stability and sensitivity sufficient for accurate monitoring of volume average brain temperatur

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 7 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 50 sensors were used. Subsets of 50 sensors were used. Thermal profiles (8–21 probes) yielded a median ΔT < 0.01 \ub0C for T90 and Tmax, with a 95%CI of −0.2 \ub0C and 0.4 \ub0C, respectively. The detection rate of Tmax≥43 \ub0C 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 cm2applicator. Thermal mapping is a valid alternative