Thermal Therapy - RF/Microwave Interaction with Biological Tissues - page 147

CHAPTER FOUR

Thermal Therapy

4.1 INTRODUCTION TO THERMOTHERAPY

Historically, using heat as a medical treatment is nothing new. Heat utilized to
treat lesions can be traced to the age of Hippocrates in 4 B.C. [1, 2]. In general
terms, thermotherapy as medical treatment has been widely used, for example,
in rheumatism and joints and muscle diseases. In these cases, EM waves, IR
rays, ultrasonic waves [3], warm water, and so on, have been used as heating
energy sources. These heating methods are seldom different from the ones
presently used in thermotherapy. Therapies using physical energy have been
recognized as a kind of physiotherapy. More specifically, these sorts of therapy
utilizing EM waves at wavelengths from several hundred to several tens
of meters have been called diathermy . They have been called short-wave or
microwave diathermy, ultrasonic wave diathermy, and so on, depending on the
difference in radiation form or wavelength. Such thermotherapies have been
put into practice in a number of frequency regions along a frequency axis as
shown in Figure 4.1. Among these thermotherapies, a hyperthermic method
for the malignant tumor has been called hyperthermia . In this chapter, we
describe the physical facets of thermotherapy, principally referring to hyper-
thermia (see Section 2.3).

4.2 HEATING PRINCIPLE

In the medical field, radiators using, for example, an EM wave or an ultra-
sound wave are called applicators . The applicators using EM waves are prin-
cipally divided into two types based on heating principle: the dielectric heating