**1.1. Tumor ablation**

Tumor ablation is defined as the direct application of chemical or thermal therapies to a tumor to achieve eradication or substantial tumor destruction. The aim of tumor ablation is

© 2013 Rubio et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

to destroy an entire tumor by using heat to kill the malignant cells in a minimally invasive fashion together with a sufficient margin of healthy tissue, to prevent local recurrence. Many ablation modalities have been used, including cryoablation, ethanol ablation, laser ablation, and radiofrequency ablation (RFA). The most recent development has been the use of microwave ablation (MWA) in tumors [1].

High Temperature Hyperthermia in Breast Cancer Treatment 85

Therefore, electromagnetic microwaves heat matter by agitating water molecules in the surrounding tissue, producing friction and heat, thus inducing cellular death via

The different manufacturers employed various strategies to obtain larger ablation zones [7]; there are currently three different manufacturers that offer commercial radiofrequency tumor ablation devices in the USA (Boston Scientific, Rita Medical and Valleylab) and an additional one in Europe (Celon). Two manufacturers (Boston Scientific and Rita Medical) employ multitined electrodes, to increase electrode surface area and volume of tissue heating. For multitined electrodes typically an incremental deployment of the tines in stages is used, with ablation at each deployment stage for a certain amount of time or until the target temperature is achieved to ensure complete ablation of the target volume. Two manufacturers use internal electrode cooling via circulation of water or saline to increase ablation zone size (Valleylab and Celon). By cooling the electrode, the tissue surrounding the electrode is also cooled. The location of maximum temperature is 'pushed' further into the tissue, resulting in a larger ablation zone size. A similar effect is obtained by infusing saline into the tissue via ports

A variety of probes have been proposed for use in MWA, with the majority being based on a coaxial structure due to the deep-seated location of many tumors and the angular symmetry of the tumor. Initial antennas based upon a coaxial waveguide structure include designs, such as the monopole, dipole and slot antennas, often encased in a polytetrafluoroethylene (PTFE) catheter to minimize adhesion of the probe to desiccated ablated tissue. A number of challenges, characteristics and trade-offs have been identified in the design of MWA probes. Challenges include the reduction of backward heating, minimization of probe diameter and impedance matching of the antenna to the surrounding tissue. Trade-offs in design involve probe diameter versus maximum application of power and ablation power versus ablation time. Early coaxial antennas developed for MWA yielded ablation zones resembling a 'tear drop', as opposed to the desired spherical shape [9]. More recent MWA probes were designed to minimize probe size, maximize ablation zone size, minimize detrimental heating of the

feedline and yield more spherical lesions, by minimizing impedance mismatch [10-12].

The first RFA clinical report was published in 1999, Jeffrey *et al.* [13] treated with RFA a small series of five women, aged 38 to 66 years, with locally advanced (stage III) breast

in the electrode this method is used by the Starburst Xli™ electrode [8].

coagulation necrosis [6].

**1.3. Ablative devices** 

*1.3.1. Radiofrequency ablation* 

*1.3.2. Microwave ablation* 

**2. Clinical applications** 

**2.1. Radiofrequency ablation** 

Nevertheless the local application of heat to treat patients with malignant tumors is not a novel concept. The Edwin Smith papyrus describes the topical application of hot oil or heated metallic implements that were used approximately 5000 years ago to treat patients with tumors [2]. The use of an electrical current to produce thermal tissue necrosis in patients with breast carcinoma also is not new: Metallic or clay-insulated electrodes were inserted into locally advanced breast tumors in the late 19th century to shrink the tumor and reduce pain and bleeding [3].
