United States radiation safety and regulatory considerations for radiofrequency hyperthermia systems

The control of Radiofrequency (RF) radiation (including microwave radiation) that is emitted by therapeutic medical devices is the responsibility of the Food and Drug Administration's (FDA) Bureau of Radiological Health (BRH). Several studies of RF emissions from various shortwave (27 MHz) and microwave (2450 MHz) diathermy devices have been conducted by the Electromagnetics Branch of the Bureau's Division of Electronic Products. BRH studies have led to a proposed standard for microwave diathermy devices operating above 900 MHz. Shortwave diathermy devices used in physical therapy situations have been found to produce relatively high levels of unintended exposures (sometimes exceeding present U.S. exposure standards) to device operators and to the nonprescribed tissues of the patient. BRH is initiating further studies to ascertain the need for controls to be placed on these shortwave devices to ensure safety and medical effectiveness. Radiation safety standards, which presently exist in the United States, allow much higher unintended human exposures than do the standards existing in the several eastern European countries. A trend to lower permissible exposures to 5 mW/cm2 or even 1 mW/cm2 is under way in the U.S. The various provisions of FDA's Medical Device regulations apply to investigational as well as commercially-marketed RF/microwave devices and require both safety and medical effectiveness aspects of performance to be addressed by their manufacturer. A set of microwave radiation safety considerations has been developed by BRH for newly emerging cancer therapy protocols which utilize microwave hyperthermia devices.