Deeper-Penetrating Waves in Lossy Media

Abstract

Hyperthermia treatment of cancerous tissue is a well-established modality to improve the effectiveness of ionizing radiation in the treatment of cancer. Electromagnetic(plane) waves can penetrate the body and heat tissue in the interior, but a principal problem in the use of electromagnetic energy for hyperthermia treatment of cancer is that at the short wavelengths which are useful for localizing the energy deposition volume, the penetration depth of electromagnetic plane waves into the tissue is very short, of the order of a centimeter, so that it is not possible to heat deep-lying tumors without overheating the surface, even using multiple radiators to superimpose the fields in the tumor. Employing frequencies at the low end of the microwave band and”skin coolers” increases the effective depth of localized heating, but only to about four to five centimeters. The only available technique to successfully overcome this problem has been the use of invasive radiators introduced into the body. Recently, however, other types of electromagnetic radiation modes have been studied which appears to offer solutions to this difficult and important problem without requiring either interstitial or intraluminal insertion of the radiating elements into the body. Surface waves are one example; these waves cannot be expressed as an angular spectrum of plane waves, unless the spectrum is extended to include complex angles of propagation. The decay rate of these waves in absorbing media is not the same as that of the usual plane waves; the skin depth for these modes can be much larger[1]. It has also been established [2] that antenna near fields are another wave type which may possess enhanced penetration depths.