Physical techniques for delivering microwave energy to tissues.

Some of the physical aspects of delivering microwave energy to tissues have been discussed. Effective penetration of a few cm may be achieved with external applicators whilst small coaxial or cylindrical devices can induce localized heating in sites accessible to catheters or to direct invasion. To heat deep tissue sites in general, systems of greater complexity involving a number of applicators with particular phase relationships between them are required. The problems of thermometry in the presence of electromagnetic fields fall outside the scope of this article. Their solution, however, is no less important to the future of clinical hyperthermia than the development of heating techniques. Finally, it should be remembered that physiological parameters such as blood flow have appreciable effects in determining the efficacy of the physical techniques described above.