Clinical trials have shown that hyperthermia (HT), i.e. an increase of tissue temperature to 39–44 °C, significantly enhance radiotherapy and chemotherapy effectiveness [1]. Driven by the developments in computational techniques and computing power, personalised hyperthermia treatment planning (HTP) has matured and has become a powerful tool for optimising treatment quality. Electromagnetic, ultrasound, and thermal simulations using realistic clinical set-ups are now being performed to achieve patient-specific treatment optimisation. In addition, extensive studies aimed to properly implement novel HT tools and techniques, and to assess the quality of HT, are becoming more common. In this paper, we review the simulation tools and techniques developed for clinical hyperthermia, and evaluate their current status on the path from ‘model’ to ‘clinic’. In addition, we illustrate the major techniques employed for validation and optimisation. HTP has become an essential tool for improvement, control, and assessment of HT treatment quality. As such, it plays a pivotal role in the quest to establish HT as an efficacious addition to multi-modality treatment of cancer.

This paper is intended as a succinct review of technology used for clinical hyperthermia therapy for cancer, as culled from a presentation at the special workshop on Thermal Medicine, Heat Shock Proteins, and Cancer at the Society for Thermal Medicine conference in Spring 2005. Following a brief overview of thermal therapy treatment options and available mechanisms for heating tissue, the paper focuses on the evolution of equipment from basic single element heating devices of the early 1980s to adjustable multi-element heating devices currently in use or in final stages of development. Representative devices from the past, present and near future are cited for further investigation by the interested reader. The paper concludes with a summary of general trends in the evolution of clinical hyperthermia techniques and a statement of current challenges remaining for the field.

A variable frequency magnetic induction heating system has been developed for localized hyperthermic treatment of deep-seated tumors via power deposition into arrays of 1-2 mm diameter ferromagnetic cylindrical implants. The frequency dependence of implant heating compared to that induced directly into tissues indicates use of frequencies below 4 MHz. Above 10 MHz, tissues are heated directly from the induced eddy currents. Thermographic analyses of temperature distributions induced in tissues equivalent phantom models and in exposed animal tissues in vivo have been performed for several implant materials and array configurations. Results of the thermal dosimetry show that the majority of tissue contained within multiimplant arrays can be heated such that the temperature rises to 55-70 percent of the implant temperature differential. The resulting tissue temperature distribution is dependent on local blood flow and array characteristics, but not significantly on tissue electrical properties. Operating the system at 1.9. MHz, we demonstrate that it is possible to raise an implanted volume to therapeutic temperatures safely, in less than 10 min, with little increase in temperature outside the array boundaries.

Locoregional hyperthermia, i.e. increasing the tumor temperature to 40–45 °C using an external heating device, is a very effective radio and chemosensitizer, which significantly improves clinical outcome. There is a clear thermal dose-effect relation, but the pursued optimal thermal dose of 43 °C for 1 h can often not be realized due to treatment limiting hot spots in normal tissue. Modern heating devices have a large number of independent antennas, which provides flexible power steering to optimize tumor heating and minimize hot spots, but manual selection of optimal settings is difficult. Treatment planning is a very valuable tool to improve locoregional heating. This paper reviews the developments in treatment planning software for tissue segmentation, electromagnetic field calculations, thermal modeling and optimization techniques. Over the last decade, simulation tools have become more advanced. On-line use has become possible by implementing algorithms on the graphical processing unit, which allows real-time computations. The number of applications using treatment planning is increasing rapidly and moving on from retrospective analyses towards assisting prospective clinical treatment strategies. Some clinically relevant applications will be discussed.

The dielectric properties of human liver were characterized over the frequency range of 0.3-3 GHz for freshly excised tissue samples of primary hepatocellular carcinoma, metastatic colorectal carcinoma, and normal liver tissues resected from the tumour margin. On average, the dielectric constant (^9; r ) of freshly excised human liver tumour was 12% higher than that of surrounding normal liver, and the electrical conductivity (`3;) of tumour was 24% higher. In order to establish suitable tissue models for human liver, the electrical properties were compared to measurements of homogenous phantom mixtures, in vitro bovine liver, and in vivo canine and porcine liver tissues. The data demonstrate that there are several animal tissues that can be used to model the average dielectric properties of human liver reasonably accurately, and use of the most readily available bovine liver appears well-justified, even when stored for up to 10 days in a refrigerator. Additionally, the dielectric properties of in vitro liver remained stable over a large temperature range, with `3; rising only 1.1%/°C in porcine liver (15-37°C) and 2.0%/°C in bovine liver (10-90°C), and ^9; r decreasing Ͱ4;0.2%/°C in both tissues. This effort identifies homogeneous solid and liquid phantom models and several heterogeneous in vitro tissues that adequately model the dielectric properties of human liver tumours for use in quantitative studies of microwave power deposition in liver.