**2. Radiofrequency energy and the RF ablation system**

Basically, the term *radio-frequency* refers not to the emitted waves, but rather to the alternating electric current that oscillates in the high frequency range. Radiofrequency is a form of electromagnetic energy. This energy is formed from waves of electromagnetic energy moving together (or radiating) through space at the speed of light. Unlike ionizing radiation (e.g. gamma rays and x-rays), which affects the chemical makeup of cells and alters their genetic code, electromagnetic energy is non-ionizing. This means that it is not strong enough to ionize atoms and molecules in cells or alter their genetic makeup. Radiofrequency energy is safer than many cancer therapies because it is absorbed by living tissue as simple heat. Regardless of the heat source, cells die when they reach a certain temperature. The main tumoricidal effect of RF ablation occurs because the absorption of electromagnetic energy induces thermal injury to the tissue. But RF energy and the heat it generates does not alter the basic chemical structure of cells. A very important part of the RF ablation system is the RF signal generator. This is where the energy deposited by the needlelike active electrode is generated. The system comprises of a closed circuit consisting of a radiofrequency generator circuit, a power amplifier circuit, and the control circuit. A power supply circuit is also included to meet the power supply requirements of the system. The energy generated by the system is delivered to the tissue by the active electrode, whereas a dispersive electrode that acts as a patient plate provides a return part to complete the circuit. A simplified block diagram of the whole system is shown in figure 1 below.

**Figure 1.** Block diagram of the RF ablation circuits

172 Hyperthermia

for HIFU procedures.

volumes of necrosis: multiple bare fibres in an array and cooled-tip diffuser fibres. The major drawback to this technique is its cost, requiring \$30,000 to \$75,000 for a portable, solid-state laser and \$3,000 per set of multiple (50) user fibres [10]. *Microwave ablation (MWA) or microwave coagulation* uses microwave tissue coagulator for irradiation. Ultra-high frequency (2450 MHz) microwaves are emitted from a percutaneously placed microwave electrode inserted into the target tissue under ultrasonographic guidance. Microwave irradiation is carried out for about 60 seconds at a power setting of 60W per pulse. During irradiation, the ultrasonographic probe is placed adjacent to the microwave electrode to monitor the effectiveness of the tumour coagulation [11], [12]. A typical microwave generator costs approximately \$65,000 [13]. *High Intensity Focused Ultrasound (HIFU) ablation* is a non-invasive treatment modality that induces complete coagulative necrosis of a deep tumour through the intact skin. HIFU uses sound energy to produce heat [14]-[16]. HIFU treatments are usually carried out in a single session, often as a day case procedure in the doctor's office, with the patient either fully conscious, lightly sedated or under light general anaesthesia. One major advantage of HIFU over other thermal ablation techniques is that the transcutaneous insertion of probes into the target tissue is not necessary. The high powered focused beams employed in the procedure are generated from sources placed either outside the body (for treatment of tumours of the liver, kidney, breast, uterus, pancreas and bone) or in the rectum (for treatment of the prostate), and are designed to enable rapid heating of a target tissue volume, while leaving tissue in the ultrasound propagation path relatively unaffected [17]. Numerous extra-corporeal, transrectal and interstitial devices have been designed to optimise application-specific treatment delivery

This chapter focuses on the discussion of principles and application of the radiofrequency ablation therapy system as a minimally invasive treatment modality for hyperthermia therapy. Detailed work completed in the use of radiofrequency (RF) energy in cancer management by developing and testing an economical and effective thermal probe that will effectively destroy volumes of pathological tumours by means of hyperthermia is presented.

Basically, the term *radio-frequency* refers not to the emitted waves, but rather to the alternating electric current that oscillates in the high frequency range. Radiofrequency is a form of electromagnetic energy. This energy is formed from waves of electromagnetic energy moving together (or radiating) through space at the speed of light. Unlike ionizing radiation (e.g. gamma rays and x-rays), which affects the chemical makeup of cells and alters their genetic code, electromagnetic energy is non-ionizing. This means that it is not strong enough to ionize atoms and molecules in cells or alter their genetic makeup. Radiofrequency energy is safer than many cancer therapies because it is absorbed by living tissue as simple heat. Regardless of the heat source, cells die when they reach a certain temperature. The main tumoricidal effect of RF ablation occurs because the absorption of electromagnetic energy induces thermal injury to the tissue. But RF energy and the heat it generates does not alter the basic chemical structure of cells. A very important part of the RF

**2. Radiofrequency energy and the RF ablation system** 
