RF/Microwave Delivery Systems for Therapeutic Applications - RF/Microwave Interaction with Biological Tissues - page 258

z

E r

H b

8

7

E 3

y

f

z
FIGURE 6.5 Isotropic spherical waves, spherical coordinates [7].

order of 64, resulting in a wavelength of approximately 15 mm at 2450 MHz.
The complicated intermediate region will, therefore, extend from 0.15 to
75 mm, encompassing the region of interest for this analysis that extends from
the surface of the angioplasty balloon radially outward into the muscle tissue
for a distance of several millimeters—typically from 1.5 to 6.0 mm (0.1l to
0.4l). The reason the intermediate region is difficult to analyze is the need for
considering both radial and tangential electric fields, shown by the electric
dipole field in Figure 6.5. These two fields are comparable in magnitude in the
range of 0.1l to 0.4l, and the contributions of both vector fields must be spa-
tially combined. The electric field density as a function of kr is shown in Figure
6.6. Figure 6.7 depicts the intermediate field as a function of w t .

6.4 RF AND MICROWAVE ABLATION [1, 10-79]

6.4.1 Fundamentals

The benefits of using heat in therapeutic medicine have been well recognized
for 150 years. Busch [10] and by Coley [10, 11] described tumor regression
after a patient developed a high fever. Since the beginning of the twentieth
century, physicians have treated various types of tumors using heat alone (heat
was found to kill tumor cells more aggressively than normal cells) and later
utilizing a combination of X-rays and systemic heat. Also used for the treat-
ment of cancer was the combination of heat and chemotherapy. The effects of
heat and the duration of heat delivery were both found to be critical. Cellu-
lar toxicity was increased by either increasing the temperature or increasing