Clinical Applications of Microwave Radiation: Hypothermy and Diathermy* Joseph B

1187 CLINICAL APPLICATIONS OF MICROWAVE RADIATION: HYPOTHERMY AND DIATHERMY* JOSEPH B. DAVIS, M.D. Director, Medical and Scientific Review Staff Bureau of Medical Devices Food and Drug Administration Silver Spring, Maryland I shall discuss the clinical applications of microwave radiation as related to hyperthermy and diathermy as related to basic issues concerned with their clinical use. In terms of the concepts of this symposium, I shall consider the term hyperthermy to relate to an increase in the temperature of localized areas of the body, as opposed to increasing the temperature of large body segments or of the whole body. Similarly, we regard diathermy as a generic term which includes short and long wave diathermy, microwave, and ultrasound. The first determination a physician who uses a drug or device to treat patients must make is one which will have considerable effect and possible fallout on the end results of his treatment. Such a determination is based on the physician's knowledge of the "safety and efficacy" of the drug or device for its intended use, an intended use clearly defined under the indications for the use of the particular drug or device. In the case of diathermy devices, the agency originally relied upon the indications and contraindications for the use of diathermy published by the American Medical Association in 1950 under the title Handbook of Physical Medi- cine and Rehabilitation.I By 1965 the agency had recognized that the information contained in *this publication was insufficient and did not reflect the state of the art for 1965. During the next 10 years we devoted considerable time and effort to determining the current state of the art. Our efforts were materially assisted by Dr. Justin Lehmann and his people at the University of Washington in Seattle, with the concurrence of the American Academy of Physical and Rehabilitative Medicine. While Dr. *Presented as part of a Symposium on Health Aspects of Nonionizing Radiation sponsored by the Subcommittee on Public Health Aspects of Energy of the Committee on Public Health of the New York Academy of Medicine and Held at the Academy April 9 and 10, 1979. Vol. 55, No. 11, December 1979 1188 J. B. DAVIS Lehmann's report dealt only with shortwave diathermy, we believe it is also applicable to the use of microwave diathermy.2 As a result of its investigation, the agency has concluded that the safety and effectiveness of diathermy devices is related solely to the production of heat. The agency has been aware of various advocates who claim that a nonthermal effect exists. Reviews of research studies submitted to the Food and Drug Administration (FDA) have failed to support such a concept. All the diathermy studies we have reviewed and analyzed, includ- ing numerous studies offered in support of this nonthermal concept, fail to substantiate the therapeutic claims made for any nonthermal effects. If such effects do exist, they will remain unknown until more sophisticated scientific technology can identify and isolate them. The indications which the agency considers acceptable for therapeutic diathermy are as follows: The use of diathermy is an adjunct procedure to produce tissue heat that may be used with conventional methods of treatment in the following conditions: 1. Secondary muscle spasms in musculoskeletal disease 2. Relief of pain resulting from muscle spasm 3. For joints where there are some acute chronic inflammatory pro- cesses 4. To improve range of motion and relieve joint stiffness associated with collagen diseases 5. Chronic periarthritis 6. Fibrositis or myofibrositis 7. Epicondylitis 8. Subacute or subchronic bursitis 9. To increase blood flow and improve circulation 10. Chronic inflammatory pelvic diseases3 The use of diathermy for therapy or treatment is based upon the absorp- tion characteristics of radiofrequency electromagnetic fields in tissues for therapeutic heating of tissues. It is also based on the physiologic responses produced and the mechanisms by which they are achieved. 2An elevation of tissue temperature into the range of 40'C. to 450C. is considered necessary for therapy to be effective.2' 3 The use of diathermy as an adjunctive treatment for any other indication is, in the opinion of the agency, an "experimental or investigative use" for which safety and efficacy have not been determined. Incidentally, in my review of some of the reports on the use of dia- Bull. N.Y. Acad. Med. 1189 HYPERTHERMY AND DIATHERMY 1189~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ thermy for hyperthermy, I found that in this experimental use for the treatment of cancers the diathermy devices employed used frequencies of 13.56 megahertz.4 The Federal Communications Commission (FCC) has assigned definite bands in the range of frequencies and wavelengths to the manufacturers of diathermic equipment for medical use.5 Such equipment for medical use must meet the frequencies and wavelengths assigned by the FCC. Failure to meet such requirements is a violation of the Federal Food, Drug, and Cosmetic Act, Section 501. The frequencies assigned for shortwave diathermy are 13.56 megahertz, 27.12 megahertz, and 40.68 megahertz. Most conventional shortwave diathermy devices use the frequency of 27.12 megahertz.5 The band frequencies assigned for microwave diathermy are 915 megahertz, 2,450 megahertz, 5,850 megahertz, and 18,000 megahertz.5 The presently avail- able microwave diathermy uses 2,456 megahertz. The 915 megahertz frequency is being used experimentally.6 In this context I would like to point out that in reference to the clinical use of hyperthermy, devices which are being used are using frequencies assigned by the FCC to short-wave diathermy and not to microwave diathermy. Some of you may wonder why I have chosen to refer to drugs and devices rather than just devices. Basically, the reason is to make several points: 1. In terms of drugs, the FDA has, since 1938, been reviewing valid controlled scientific research to substantiate the safe and effective use of drugs for specific indications as the basis for the agency's approval of drugs for use by physicians. Physicians, although occasionally upset by the length of time the agency takes to approve a particular drug, appreciate the assurance of knowing the drug is safe and effective when they prescribe the drug. 2. On the other hand, devices have never been subjected to the same consideration as was required for drugs. In other words, the FDA has never approved any device as safe and effective for its intended use. Most physicians who use medical devices in their practice have mistakenly assumed that the agency has approved such devices simply because the government permits them to be sold. Equally unfortunately, the valid, controlled, scientific research conducted by experts who are qualified by training, knowledge, and experi- ence to do such research has in most instances not been accomplished. Vol. 55, No. 11, December 1979 1190 J. B. DAVIS Most of the evidence to substantiate the safety and efficacy of medical devices is based on subjective clinical impressions of the users. While such impressions are not without a certain historical importance, they fail to meet the usual scientific standard of valid, credible, and reliable evidence. The FDA, in an effort to correct this long-standing state of affairs, recommended legislation which was enacted as the Medical Device Amendments in May of 1976. These amendments provide additional regulatory authority to determine that medical devices are also safe and effective for their intended uses. Under the Medical Device Amendments the Advisory Classification Committees have classified diathermy devices, based on their usual and customary use in physical therapy treatments, which depends upon the production of heat in the tissues treated, as Class II. Classification in Class II is based on the assumption that sufficient scientific evidence exists to substantiate the safety and efficacy of diathermy devices for the usual and customary use, and that performance standards-on a generic basis-can be Written. The present concept of the Bureau of Medical Devices is that a standard can be written which will prevent hazards related to the use of the device. These hazards are identified by the Advisory Committee in their classification of the devices. The administrative authority over diathermy devices has been transferred from the Bureau of Medical Devices to the Bureau of Radiological Health. A device which is used medically for a condition which was not considered usual or customary when it was classified is considered to be experimental or investigative (Class III) for that particular new use of indication. To establish the use of the device for that indication will require the accomplishment of all the various requirements necessary to provide valid, controlled scientific research evidence to substantiate the safety and efficacy of the device for the new intended use. Developing such scientific evidence will no longer be simple, conducted in a hit-or- miss fashion by inexperienced or unknowledgeable investigators with little or no knowledge or understanding of scientific methods and principles in the conduct of a scientific study. In this connection, the agency is proposing certain basic ground rules to be met before the agency will consider any research as acceptable for review when offered as evidence to substantiate the safety and efficacy of the device for its intended use. For those who are familiar with the IND and NDA

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