Extensive research has been conducted on the unique characteristics of tumor bearing tissue and the treatment thereof by various techniques. One discovered characteristic of tumor bearing tissue is that blood flow through the tumor is substantially less; for example, 2% to 15%, than blood flow through surrounding normal tissue (Radio Frequency Therapy JAMA 5/17/76, Volume 235, No. 20, LeVeen et al). Because of this vascularity of tumor tissue, under heat therapy such tumor tissue acted as a heat reservoir, was unable to dissipate heat at the same rate as surrounding normal tissue, and therefore reached temperatures from 5.degree. C. to 10.degree. C. higher than normal tissue under certain treatment procedures. Such temperature differential suggested bringing tumorous tissue to temperatures in the range of 45.degree. C. to 50.degree. C., at which the tumorous tissue would be destroyed or subject to substantial regression, with preservation of normal tissue at physiologic temperatures. Substantial regression of the tumorous tissue may be a beneficial adjunct to other forms of treatment of tumors, such as surgery, radiation, chemotherapy, and immunotherapy.
Medical diathermy, used for decades in musculo-skeletal disorders, has limitations to deep heating imposed by the inability to provide for surface tissue protection by cooling. Provision of surface tissue at physiologic temperatures, while causing deep musculo-skeletal heating, would broaden the applications for medical diathermy in varied disease states (sprains, strains, arthritis, etc.).
Various ways of heating body tissue have been proposed. Localized application of heat by use of electromagnetic energy derived from radio frequency generators has been conducted in the ranges of ultrasonic frequencies 0.8-1.0 MHz, shortwave frequencies 13-27 MHz and microwave frequencies 915-2450 MHz. Most relevant to (but not a limitation of) the present invention is the shortwave frequency, which is described in said publication on Radio Frequency Therapy. Shortwave generates less heat in fat with deep penetration and is the longest band width (13.56 MHz) approved by the Federal Communications Commission for medical use.
One of the problems encountered in localized application of radio frequency waves to tissue is that of severe burning of skin and subcutaneous tissues. Surface cooling in a microwave field at 915 MHz has been proposed by using a microwave antenna in non-surface contact with the skin and blowing cooled air onto the skin through the space between the radio frequency emitter and the skin. Another cooling method is described in application of heat to muscle in human subjects with a 915 MHz microwave contact applicator in which coolant was circulated through a dielectric cooling plate of a microwave applicator in which the emitter was an antenna in a tuned cavity type applicator, the emitter antenna being relatively widely spaced from the dielectric cooling contact plate. (Archives of Physical Medicine and Rehabilitation, March 1970, pages 143-151, "Evaluation of a Microwave Contact Applicator," Lehman et al and "Muscle Heating in Human Subjects With 915 MHz Microwave Contact Applicator," LeLateur et al.)