Advances in electronics and electromagnetic theory have set the stage for an unprecedented drive towards the development of medical devices with various diagnostic and therapeutic applications. RF (hundreds of kilohertz to a few megahertz) and microwaves (hundreds of megahertz to approximately 10 gigahertz) are forms of nonionizing radiation, unlike much higher frequencies (above visible light) in the EM spectrum, which are ionizing. Therapies using EM sources at RF and microwave frequencies have been called thermal therapy. These therapies have been applied in a number of frequency regions along the EM spectrum, as shown in Figure 8.1. Included among these thermotherapies are hyperthermia and thermal ablation.