RF/Microwave Delivery Systems for Therapeutic Applications - RF/Microwave Interaction with Biological Tissues - page 261

responsible for the abnormal cardiac rhythm can be eliminated. In urology,
similar systems are used to treat BPH, a condition resulting from overgrowth
of the prostate leading to obstruction of urine flow. In the last few years,
several otolaryngological centers around the world have been utilizing RF to
treat upper airway obstruction and alleviate sleep apnea. Although the treat-
ment of cancer by means of RF and microwaves has met with various degrees
of success and is well documented, many oncological centers are not yet using
these modalities. However, renewed interest in high-temperature localized
heating for the treatment of liver, kidney, and breast cancers has led to results
showing a prolongation and improvement in the quality of life.
In the case of renal cancer, an RF needle ablation device is being utilized
to treat patients with kidney tumors 0.5-3.0 cm in size. Such RF needles are
inserted directly into the tumor and are heated to approximately 100°C for
10 min. In the case of RF treatment for hepatic neoplasm (liver cancer), a
multitude of needles having thermistors at their tips for temperature control
are being utilized. Research is currently being conducted on the utilization of
microwave energy for the treatment of bladder cancer by means of
transurethral microwave needle ablation (TUMNA), a procedure that utilizes
a simple device under local, or lower lumbar, anesthesia. The patient is exam-
ined by cystoscopy to confirm the position and tumor size. The needle antenna
is advanced into the bladder, then inserted into the tumor. Power as high as
100 W, depending on the tumor size, is delivered for about 60-90 s.
Radio frequencies at around 500 kHz are also used in the treatment of other
medical conditions such as GERD and for the tightening of damaged liga-
ments. It is important to mention that new therapeutic applications of
RF/microwaves are continuously being developed. Microwave-assisted lipo-
suction, for example, is a technology that has undergone successful in vivo
animal testing and is awaiting human trials (Fig. 6.8 a ).

6.4.2 RF Development

The utilization of RF in medicine dates back to the 1920s, when research was
conducted by W. T. Bovie, who pioneered the use of RF in surgery for both
cutting and coagulating [73]. In the 1950s, S. Arino and B. J. Covos were the
first to utilize and commercialize an RF system for use in neurosurgery [74,
75]. The RF generator is a source of RF voltage that is applied between two
or more electrodes connected to a tissue to be ablated. The heating distribu-
tion is a function of the RF current density, where the greatest heat is gener-
ated in the region of the highest current density. The lesion size is a function
of the size of the electrodes and the resulting electrode-tissue interface.
Since the publication of New Frontiers in Medical Device Technology [1]
and of Chapter 2.14 in RF and Microwave Handbook [78], other RF applica-
tions of about 500 KHz have been developed. However, instrumentation such
as the RF generator has remained essentially unchanged in most applications
(Fig. 6.8 b ), although some of the improvements are important. Some of these