On the Safe use of Microwave and Shortwave DiathermyUnits

Dipthermy is a common treatment modalityused> to relieve pain through localized heating.This paper briefly discusses the mechanismsthrough which heat is generated in tissue andthe absorption characteristics of the appliedelectromagnetic radiation. The adverse effectsof this radiation are reviewed with particularemphasis on the current exposure limits foroperators and non-patients in the vicinity ofdiathermy devices.

The newly introduced codes of practice forthe 'Safe Use of Shodwave (Radiofrequency)andlAicrowave Diathermy'are also discussed.

'i

VINCENT DELPIZZO

Vincent Delpizzo, Ph.D., is a physicist in the non­ionizing radiation group of the Australian RadiationLaboratory and is involved in research on the healthhazards of electromagnetic radiation.

KENNETH HENRY JOYNER

Ken Joyner,Ph"D., is Principal Scientist at theTelecom Research Laboratories where he is con­ducting research in the interaction of electromag­netic radiation with matter.

Diathermy is a form of therapywhich utilizes electromagnetic radia­tion to induce heat inside the patient'sbody. This leads to increased bloodcirculation which is believed to inducefaster healing. Diathermy is used inavariety of conditions including sprainsand strains, muscle and tendon tears,chronic rheumatoid arthritis, tenosy- c

novitis, bursitis and synovitis.The medical efficacy of this treat­

ment ,has 'been the subject of somecontroversy, while the potential haz­ards posed by the high power,(> 200W)electromagnetic radiation emitted by adiathermy machine are certainly not tobe neglected.

In a Canadian survey of shortwaveand microwave medical devices (DHW1980) only 54.3 per cent of the short­wave diathermy operators were de­scribed as trained (38.5 per cent of therespondents provided no reply while7.3 per cent admitted being untrained).The. same survey indicated that 8 percent of the treatments involved irra­diation of the pelvis (including treat­ment of the reproductive and urinary"systems) and a similar percentage in­volved irradiation of the head.

Although similar data is not avail­able for Australia, reports of unwiseand potentially hazardous practices inthe use of diathermy have caused dis­quiet among health regulatory author­ities and have prompted the NationalHealth and Medical Research Councilto issue a uniform code ofpractice forthe safe use of diathermy machines.The code was produced in two slightlydifferent versions, one for microwaveand one for shortwave (radiofre­quency)'units. Both codes are includedin Appendices AandB of this article.A similar code, has been established inCanada (DHW 1983).

Shortwaves and Microwaves

Technically, the term rediofrequencyradiation refers to that portion of thefrequency spe..ctrum useful for radio­communications ie 10kHz to 300 GHz.However, it is not uncommon to fur­ther divide this frequency range intoradiofrequency (10 kHz to 300 MHz)and microwave (300 MHz to 300 GHz)regions. This latter convention has beenadopted for this paper and the codes.

Because of the competing demands ofvarious microwave and radiofrequencyusers, specific bands have been allo­cated by the International Telecom­municationUnion for industrial, scien­tific and medical (ISM) applications.In Australia diathermy' units are al­lowed to operate in only two of theISM bands, namely the microwaveband of 2450 MHz (wavelength = 122mm) and the shortwave band of 27.12MHz (wavelength = 11.1 m).

The absorption properties and themethods of application associated withthese two frequencies are considerablydifferent and therefore the heatingmechanisms and, more importantly, theresulting heating patterns vary.

The interactions of electromagneticfields with tissue can be considered ona macroscopic or microscopic level. Onthe microscopic level, three basicma­chanisms underlie the interactions.These include:(1) the orientation of electric dipoles

that already exist in the atoms andmolecules in the tissue;

(2) polarization of atoms and mole­cules to produce electric dipoles;and

152 The Australian Journal of Physiotherapy. Vol. 33, No.3, 1987

The Safe use of Microwave and Shortwave

Figure 1: Inductive (a) and capacitive (b) applicators

(3) displacement or drift of conduction('free') electrons and ions in tissue.

Heat can be generated in tissue ineach of these three interactions. In thefirst .two cases the heat is generatedthrough .friction associated with themovement of atoms and molecules fol­lowin.g~the time variation of the electricfield. I'Q the case of displacement ofconduction charges, the collision ofelectrons and ions with atoms and mol­ecules of the tissue produce heat. Notethat it is only the internal electric fieldthat transfers energy to the tissue.However,magnetic fields will induceelectric fields in tissues thereby gener­atingheat. Thus both electric and mag­netic fields produced by the diathermyapplicator are important with respectto the generation of heat.

All three of the above interactionsare described by the macroscopic pr,op­erty of tissue, called. the 'complexpermittivity', which represents thedielectric constant and loss factor ofthe tissue. The complex permittivity oftissue is a function of frequency and,as a result, the propagation and atten­uation of electromagnetic waves arealso dependent on th~ frequency(Schwan .1954, Schwan 1970).

In shortwave diathermy the patientis made part of the electrical circuit ofthe generator by using either an in­ductive coil (Figure la) or a capacitortype applicator (Figure Ib). A variablecapacitor in the unit is tuned· to matchthe generator with the patient-appli­cator circuit, thus.achieving maximumpower transfer.

If a capacitive applicator is used, thepatient is subjected to an oscillatingelectric field which causes molecules inthe tissue to vibrate and produce heat.In the case of the inductive applicator,primary heating is due ·to eddy currentsinduced by the oscillating magneticfield. The heating pattern is determinedby th.e type of applicator, by its sizeand by its position relative to thepa­tient.

For a microwave unit, the wave­length of the radiation (122mm) ismuch smaller than the overall dimen-

a

sians of the patient and therefore thedirectionaI.properties .of the radiationare important to its operation. Themicrowave radiation is emitted by asmall antenna and directed towards thearea of treatment by a suitably shapedreflector. The antenna and the reflectorconstitute the applicator. Differenttypes of applicators can be used withthe same unit to obtain different heat­ingpatterns.

The heating effect of microwaves isdue to energy dissipated by the watermolecules in the tissues as they vibrateto follow the oscillations of the electricfield. The heating pattern is determinedby the penetration characteristics of theradiation and by the type ofapplicator.Like light, microwaves can be trans­mitted t reflected, refractedandab­sorbed by different media. Reflectionoccurs at the interface between twomedia through which the radiationpropagates at differing velocities (eg airand skin, muscle and fat) (Schwan1954).

Absorption is the transfer of energyfrom the electromagnetic wave to the

medium which it is penetrating. Tissueshaving a high water content absorbmore than tissues such as fat or bone.Within a given medium absorption de­pends on the electrical properties ofthe medium, on the frequency of theradiation and the distance travelled bythe wave. In general, in the radiofre­quency range, absorption increases withincreasing frequency. At the frequencyof 2450 MHz, the amplitude of theelectric field falls by approximatelytwo-thirds after propagating for 20 mminto tissues of high water content. Asthe power of the radiation is .propor­tional to the square of the electric field,only about 10 per cent of the power istransmitted past that distance.

The rate· at which energy is impartedto a given mass of tissue is expressedby the specific absorption rate (SAR)which is measured in WIkg. The SARis calculated by the relationship (Wit­tersetol 1979):

4.19 x lcrC TSAR

t

The Australian Journal of· Physiotherapy. Vol. 33, No.3, 1987 153

The Safe use of Microwave and Shortwave

Occupationallyexposed *

whereC specific heat of tissueT temperature rise in tissuet time of energy deposition in the

tissue.

The SAR can also be expressed interms of the electrical properties of theabsorbiqg tissue (Osepchuk 1979):

--L . . 2SAR = .2p W€o € tan oEin

Wherep is the mass density of the body,

in kg/m3

fa is the permittivity of free space,in farads/m

€ is the relative dielectric constanttan 0 is the loss tangentw is the radian frequency given by

w= 211'"fEm is the electric field in volts/m at

the point in ·the body.

Experimental and clinical researchindicates that therapeutic responses willoccur as a result of elevating tissuetemperatures in the range 41° to 45°CrequiringSARs from 50 to 235 W/kg(U.S.A. Federal Register 1980) in thetreatment area (Guy etal 1974).

Because of the presence of differentlayers of tissue with different physicalproperties and because of the resultingcombined effects of absorption and re..flection, it is exceedingly difficult toaccurately estimate the dose ofradia­tion delivered to a specific organ. Inpractice the only indicator available tothe therapist is the thermal sensationexperienced by the patient and eventhis may not reflectacturately the pos...sible presence, for example, .of 'hotspots' in an area which does not pos..sess an adequate number of thermalreceptors. The power meter incorpo­rated in the unit's console indicatesonly the" power emitted by the gener­ator, not that delivered to the patient.

potentially hazardous, not only to thedirect user, but also to other personswho may be unintentionally exposed(WHO 1981).

At the Warsaw International Sym­posium on biological effects and healthhazards of microwave radiation in 1973it was ag!eed that, from the point ofview of the biological effects, micro­wave· power densities could be dividedinto the followiIfgranges:-High power densities, greater than

10 roW/cm2 at which distinct ther­mal effects predominate.

- Medium power densities,between1 mW/cm2 and 10 mW/cm2,whereweak but noticeable thermal effectsexist.Low power densities, belowlroW/ cm2

, where thermal effectsdo not appear to exist but othereffects have been reported. The ex­act nature of these non-thermal ef­fects continues to be the subject ofmuch controversy as they are sub­jective in nature and difficult toquantify (see, .for example: Sym­posium on Health Aspects of Non­ionising Radiation 1979, Steneck1984).

Although no formal agreement hasbeen reached, a similar classificationmay be applied to the shortwave fre­"quency of 27.12 MHz.

The thermal effect of electromag­netic. radiation which has already beendiscussed may lead toa number ofdetrimental effects from lesions .inspecific organs to gross thermal stressfrom hyperthermia. The severity of the

"Table 1:Maximum permissible exposure .Iimits

Frequency(MHz)

effect depends on many factors includ­ing ·the nature of the organ exposed,the intensity and duration of the ex­posure, on the size and the health con­dition of the subject exposed (SAA1985).

For the operators and members ofthe public, including other patients, re­ceptionistsetc., any effect induced inthem is unwanted and therefore theexposure must be limited to the levelsprescribed by the Australian ·StandardAS2772(SAA 1985) and reported inTable 1. Occupationally exposed indi­viduals are persons exposed to radia­tionas a direct consequence of theiremployment, which in this case meansthe operators of diathermy units.

Surveys of shortwave diathermy de...vices in the USA (Ruggera 1980) .andCanada (Stuchlyet a/1982) and resultsof measurements performed by the au...thorshave shown that, in general, ifthe operator remains approximately 1mfrom the applicator and, in particular,O.5m from the cables his or her ex­posure will be within the recommendedlimits.

However, exceptions to this rule havebeen reported. It was shown in theUSA survey (Ruggera 1980) that oneshortwave diathermy device producedunwanted power densities well in excessof the recommended limit at a distanceof 1 m from the applicator. Althoughthe authors of that survey did not com­menton that result, other diathermydevices surveyed, of the same modeland used for the same· treatment mo...dality, produced much lower power

General

* ie persons exposed as a consequence of their occupation,in this casethe operator.

Personnel Exposure

Exposure LimitsLike many sources of electromag-;

netic radiations, diathermy devices are

27.12

2450

1.22 mW/cm2 0.24 ·mW/cm2

0.2 mW/cm2

154 The Australian Journatof Physiotherapy. Vol. 33, No.3, 1987

The Safe use of Microwave and Shortwave

Figure 2: Simultaneous use of more than one unit increases the chance ofoverexposure of the operator. The radiation levels reported in the figures wereobtained during normal therapeutic use of the machines.

The occupational exposure limit mayalso be exceeded if more than onediathermy unit is operating within 2 mof each other (Figure 2). We havemeasured the field existing in the spacebetween a number of diathermy units(both microwave and shortwave), dur­ing the administration of commontreatment modalities. The recorn­mended limit was exceeded between theshortwave devices, but not between twomicrowave devices, presumably due tothe greater directionality of the micro­wave applicators.

2m

.1.6 mW/cm2

Shortwavekneetreatment

1m

.0.53 mW/cm2

Microwave Shortwavehand treatment, hand treatment

.O.8mW/cm2

DDShortwave Microwaveknee treatment shoulder

treatment

excess of those recommended for oc­cupationalexposure.

It is not impossible that persons notdirectly involved in the use of the ma­chine will be subjected to doses in ex­cess of the recommended limit (Figure4). It must be remembered that forthese persons the recommended limitis five times lower than that applicableto the operator. Normally however thissituation is unlikely to occur becausethe power density varies inversely asthe square of the distance.

Careful planning of the patient treat­mentarea can minimize these risks.Advice on the matter can be obtainedfrom the relevant state authorities listedin Appendix C.

Hazards to the PatientObviously these 'safe' limits do not

apply to the patient as the inductionof thermal effects in the patient's bodyis the purpose of diathermy; however,the line between therapeutic and harm­ful dose can be uncomfortably thin.

In the specific case of diathermy thedetrimental effects of electromagneticradiation may appear in a number ofinstances as a consequence of inappro­priate practice or because ofa particu-

Shortwave thightreatment

o1m

1.6 rnW/cm2

Shortwaveknee treatment

Shortwave hand treatment

Planning of Patient Treatment AreaOver-exposure to persons other than

the patient may result from inadequateplanning. To illustrate ,this we haverecreated in our laboratory two ex­amples of badly planned treatmentareas and surveyed the radiation' levelsin positions which could conceivablybe occupied by the operator and/ormembers of the public.

Figure 3 illustrates how reflectionsfrom a filing cabinet and a wall­mounted,metallic instrument panelmay produce, within one, metre froma microwave applicator, local fields in

densities at a distance of 1m from theapplicator. It would appear that theshortwave diathermy device in questionmay have had either faulty cables, con­nectors, or applicator. There were otherdevices in this survey that exceeded thelimits ata distance of 1 rn.

We'htlve tried to replicate this resultusing a$iemens Model 808 device witha wing 'applicator. An ,experiencedphysiotherapist was asked to adminis­tershortwave treatment to the thigh ofa patient using a normal therapeuticirradiation level. The environmentalradiation level was measured at severalpoints at a distance of 1 m from theapplicator, using a HoladayHI3002monitor fitted with a E-field probe. Wewere 'able to obtain a level in excess ofthe standard limit only if the cableswere positioned so that they were within0.5 m of the detector.

Also in the Canadian survey (Stu~hlyet af 1982) high power densities weremeasured at, we ,assume, the consoleof a shortwave diathermy device. Thisresult was attributed, in part, to thetreatment regime which consisted oftreating both knees using large diam­eter air spaced electrodes~ ,Again, theonly way 'we could replicate this result,was to be within 0.5 m of the cable.

In order to help ensure that opera­tors are not exposed in excess of therecommended limit, the codes pre­scribe the minimum distances that theoperator should maintain from the ap­plicators and leads:

- for shortwaves: 1m from the ap­plicators and O.5m from the 'leads;short excursions closer to the elec­trodes are permitted but only whennecessary (DHW 1983).

- for microwaves: 2 m from the ap­plicators, but remaining outside thedirect beam.

The distance of 2 m should ensurethat i~ reflections occur (it can be shownthat, due to the possible formation ofstanding waves, power densities mayincrease bya factor offour in this case)the operator exposure will be withinthe J;ecommended limits.

The Australian JQumal of Physiotherapy. Vol. 33, No.3, 1987 155

The Safe u.seofMicrowB.ve and Shortwave

~:0 ~O :0 Eo +fE, =lEo

I-=-

At the frequency ofoperation ofshort­wave diathermy, the ratio between thetwo coefficients is such"that the electricfield in the fat layer is considerablylarger than in the muscle. Conse­quently as the power absorbed is pro­portional to the square of the electricfield, the power absorbed in~he fat isalmost eight times that absorbed inmuscle.

When the fat layer is not too thick,capacitive applicators may still be used,with care, but .they should be' avoidedwith obese patients (ie persons 20 percent or more over the normal weightrange).

However, if the electric field .is par­allel to the interface between muscleand fat, as is the case for microwavetreatment (Figure 6), the boundarycondition requires that Er=Em• Inthis case muscle absorbs more powerthan fat, although the efficacy of the

Figure 6: The electric field of the mi·crowave radiation emitted by diathermyapplicator is parallel to the fat-muscle I

interface.

FigureS: Alignment of polar molecul~sin the dielectric reduces the electriCfield between the capacitor's plates.

~+-

(J \)~+- +

~

• 1.9mW/cm2

Ee

...::- 1 metre ~.. 1.1 mW/cm2

(boundary condition for the electricfield perpendicular to the fat and mus­cle layers)

of radiation there are some situationswhere they can be caused even by nor­mal therapeutic doses.

The·subcutaneous fat layer is moreeasily heated than the muscle tissueduring shortwave treatment using ca­pacitor type applicators. This effect,beside being a consequence of thepaucity of blood flow in the fat, is alsodue to the different intensities of theelectric field in the two layers (Guyetaf 1974). This can be explained usingan idealized plane wave (Christensenet af 1981).Whenan electric field Eois applied to a dielectric, such as fator muscle, it causes a realignment ofthe electric charges associated with itsmolecules (Figure 5). The charges thusrealigned create an induced field (E)which opposes the applied field. As aresult, the field (EJ within the dielec­tric is less than Eo.

We can write Eo/Ed = k, where kis the relative dielectric constant of themedium.

At the boundary between fat andmuscle we must have

CavityWalt·

(2 x10 mmplastersheets)

Bums and ScaldsBeside the obvious case ofa burn or ie

scald resulting from an excessive dose

larsusceptibility of the patient to in­jury.

In a recent Canadian survey (DHW1980) a small number (- 4070) of re­spondents have reported the incidenceofadverse effects, including increasedpain, burns and pacemaker interfer­ence, in some of their patients.

• 0.5 mW/cm2

Figure 4: Persons other than the oper- ~ator can also be exposed to radiation.In this example, the microwave powerdensity at the receptionist's waist .levelwas measured to be =0.5 mW/cm2

,

which is 2.5 times the recommendedlimit. The distances between therecep..tionist and the applicator was 2.1 m.The microwave output was 180 w.

Figure 3: The presence of reflecting objects may cause hazardous radiation levelseven behind a microwave applicator.

156 The Australian Journal of Physiotherapy. Vol. 33, No.3, 1987

The Safe use of Microwave and Shortwave

treatment is reduced, as there is no shown that elevations of core temper-therapeutic value in heating the fat ature in excess of 2.5°C during thelayer. For instance, it can be shown organogenesis stage of pregnancy re-that less than half of the incident power suIt in increased resorption of fetusesreaches the muscle if the fat layer is 2 and in congenital birth defects of thecm thick. central nervous system. The latter, and

An accurate estimate of the rate of the associated clinical disorders in an-temperature increase in fat and muscle imals, have been reviewed extensivelytissuei~very difficult to obtain because by Edwards (1978, 1981).of the 'many variables involved. The While experimental data is lackingultimate decision on the use of diath- for primates, retrospective and pro-ermy units with overweight patients spective studies of mothers with febrilemust be left to the professional judge- illnesses in the first trimester indicatement of the therapist. Shortwave ap- that hyperthermia has similar terato-plicators that have predominantly a genic effects on the developing humanmagnetic field output (egcoil, monode, fetus (Smith 1978, Clarren 1979)..diplode) are the most suitable to pro- A recent epidemiological study ofduce deep tissue heating without much birth outcomes among physiotherapistsrisk of burns to the fat layer (Kloth in Sweden has found a higher than1984). normal incidence of dead or mal-

Perspiration must be allowed to formed infants bornto those operatingevaporate freely not only to help dis- shortwave diathermy units (Kallenetsipate body heat but alsobecause~ater al 1982). Rubin and Erdman (1983)is heated by the electromagnetic radia- reported four cases of patients beingtion. In the case of microwaves this is treated with microwave diathermy forthe major heating mechanism. Drop-chronic pelvic inflamation who becamelets of perspiration on the skin can pregnant during the course of the treat-rapidly reach a very high temperature ment and therefore received-microwave(Kloth 1984). Only dry towelling should exposure to the pelvis just prior to andbe used when this is necessary to sup- during early pregnancy. In one case theport the induction coil used with some pregnancy resulted ina miscarriage.shortwave therapy regimes, otherwise Three similar cases, this time involvingall clothing, bandages and coverings shortwave diathermy, were reported byshould be removed. Nylon and other C Imrie (1971). One of the pregnanciessynthetic fibres are particularly unsuit- terminated in a miscarriage. Ghiettiable because they retain the moisture (1955) reported the birth of a mal-against the skin. If, in the course of a formed, -immature, convulsive infantmicrowave or shortwave treatment, whose mother had been treated withperspiration appears on the patient's shortwaves during the frrsttwomonthsskin, the treatment should be inter- of pregnan.cy. Although no direct linkrupted and the skin dried. For this can be established between these ad-reason and to make sure that the pa- verse pregnancy outcomes and thetient remains in the proper position and diathermy treatments, these cases, to-most importantly, does not look to- getherwith the results obtained fromwards the applicator, .it is necessary animal experimentation, suggest that itthat the patient not be left alone during is wise to avoid microwave and/orthe microwave treatment. shortwave exposure during pregnancy.

Teratogenic EffectsTeratogenic effects following mater­

nalhyperthermia have beenexperi­mentally demonstrated in a number ofanimal sp.ecies,notably the guinea pig(Edwards 1967, 1978). It has been

Specific PrecautionsApart from the normal contraindi­

cations such as open wounds, haemor­rhage or acute infections, the followingare more specific risks.

If the irradiated region contains acancerous growth, temperature tendsto develop in the tumor higher thanthat in surrounding normal tissue(Babbs 1981). This increase in the tem­perature leads to the destruction ofcancerous cells and therefore, diath­ermy is sometimes used as <a therapyfor cancer patients. However, if thetemperature is between 40 and 41.5°C,the growth rate of tumors is accelerated(Burr 1974). The use of diathermy ·istherefore contraindicated in patientswith evidence of cancer, unless it ispart ofa specific cancer therapy re­gime.

Metal intensifies the electromagneticfields, potentially leading to hazardoustemperature increases. Therefore thetreatment of patients having metallicimplants in the treatment area is con­traindicated. For the same reason allmetal such as rings and watches shouldbe removed from the area oftreatment.

The presence of a·cardiac pacemakerin a patient also constitutes acontrain­dicatlon. The risk, obviously, dependson·the treatment regime, being minimalfor treatment of the extremities.

Diathermy is also contraindicatedwith patients who do not possess nor­mal pain and thermal sensation in thearea to be treated.

Adverse Effects on the EyeAcute exposure may cause injury to

the eye, particularly using frequenciesranging from 1 GHz to 10 GHz (andtherefore including the freqliency ofoperation of microwave diathermyunits). Cataract formation may be in­duced in animals by exposure for 1hour to power densities in the 150 to200 mW/cm~range (Ruggera 1980).These levels are similar to those pro­duced by microwave diathermy units.Retinal lesions may also occur (Cleary1980).

Unintentional irradiation of the eyesis a real .possibility due to the limiteddirectionality of the applicators.Bas­sen etal (1978) have reported that mostnon..contact applicators exhibit a highlevel of radiation 'leakage', that is ra"

The AustralIan Journal of PhysIotherapy. Vot 33, No.3, 1987 157

The Safe use of Microwave and Shortwave

diation delivered to the environmentrather than to the target tissue. Levelsup to 44mWIcm2 were measured at 5em from the applicator.

The danger that microwaves pose tothe eyes, cannot be overcome easily.Goggles do not offer adequate protec...tioll-\because, as the dimensions of theeyepie~esare comparable to the wave­length':bf the radiation, the diffractionaround the edges is significant. It hasalso been shown (Griffin 1983) thatmetal rimmed ,spectacles enhance thefield near the eye. Therefore it isrecommended that the head never beirradiated with microwaves except inthe course of cancer therapy.

Effects on the GonadsThe testes are also particularly sen...

sitive to hyperthemia. Exposure of thescrotal area to microwaves at 2450 MHzand at power densities greater thah 50mW/cm2 resulted in varying degrees oftesticular damage (such as oedema,atrophy, fibrosis and coagulation ne­crosis of seminiferous tubules) in lab...oratory animals (Leach 1980, WHO1982, Manikowska-Czerska 1985). Theoveries are also susceptible to hyperth...ermia; ,however,being located deep inthe pelvic cavity they are not normallyaffected by microwave diathermy(Elder 1984). Shortwaves, on the otherhand, can penetrate many centimetresof tissue and may put the ovaries atrisk.

Conclusion

We have reviewed the hazards pre­sented by the high radiation level as...sociatedwith shortwave and micro­wave diathermy.

We have pointed out the possibilityfor the operator to be exposed to levelsexceeding those prescribed by the ap...propriatestandard.

Patients ,may also be at ,risk if theoperator is untrained and/or carelessor if the patient is unco...operative egunable to understand and follow theinstructions and appreciate thepoten­tial risks.

It is therefore concluded that theseunits can only be operated by registeredhealth professionals as defined in theCodes (Appendices A and B).

AcknowledgementWe wish to thank Mrs JoanMc­

Meeken and Mr Alex Ward for usefuldiscussions and for allowing us to carryout measurements on the diathermyunits at the Lincoln Institute of HealthSciences, Victoria.

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Symposium on Health Aspects of non-ionizingradiation (1979), Bulletin of the New YorkAcademy of Medicine, 55, 973-1296.

USA Federal Register, (1980), Microwave Diath­ermy products; Performance standard~ 45, (147).

Witters OM and Kantor G (1979), Free~Space

Electric Field Mapping of Microwave Diath­ermy Applicators~ HEW Publication (FDA)79.8074.

WHO (1981), Environmental Health Criteria 16- Radiofrequencyand Microwaves~ WorldHealth Organization - Geneva.

WHO (1982), WHO Regional Publication Euro­pean Series 'No. 10, Non-ionizing RadiationProtection~ Copenhagen, p. 111.

158 The Australian Joumalof Physiotherapy. Vol. 33, No.3, 1987

The Safe use of Microwave and Shortwave

Appendix ACode of Practice for the SafeUse of Microwave Diathermy

Units (1985)*

IntroductionThe therapeutic use of heat produced by

microwtlye radiation absorbed in the bodyis called*, microwave diathermy. The heatincreases the .flow of blood in the tissuesthrough dilation of the blood vessels. Thisin tum increases capillary pressure, cellularmembrane permeabilitY,and metabolic rate,causing a more rapid transfer of nutrientsfrom the·blood across cell membranes. Theseactions may reduce pain and promotequicker healing.

A microwave diathermy unit is a devicedesigned to generate microwave radiationand transfer it, via a coaxial cable and aradiating antenna, to the area to be treated.The antennais incorporatedin an applicatorwhich· has the function of directing the ra­diation towards the area to be treated.

These devices are capable of generatinga sufficiently high levelaf radiation thatthere may because for concern for thesafety of the eyes, the gonads and, in thecase of pregnant patients, the foetus. It isclaimed that radiation from microwavediathermy applicators has caused cataractsin patients being treated for sinus condi­tions. The eyes of patients being treated fora neck or shoulder injury could also beinadvertently subjected .to ·stray radiation.Improper use of the machine may result inburnsand/or scalds and tissue or organdamage. Care must also be taken to avoidsubjecting the operatorand/or the publicto radiation levels exceeding those pre­scribed in the Australian standard AS 2772(Maximum Exposure Levels - Radio..frequency Radiation - 300kHz to 300GHz). It must be noted that the level ofradiation present in the vicinity ofadiath­ermy unit may .be increased by reflections.

Care must be taken to ensure that themicrowave radiation does not cause inter­ference with other equipment.

This Code sets down appropriate rulesand procedures to avoid excessive and/orunnecessary exposure to microwaveradia­tionbut should be read in conjunction withany State/Territory regulations coveringtheir use.

DefinitionsMicrowave diathermy unit means a device

using electromagnetic energy in the micro­wave frequency range (300 MHz to 300 GHz)

• Reproduced by courtesy of The National Health andMedical Research Council.

for therapeutic purposes. The unit includesapplicators, the microwave generator, andall associated electronics, controls and en­closures. In Australia the only approvedfrequency for microwave diathermy treat­ments is 2450 MHz.Treatment means the use of a microwavediathermy unit ana human being to treata symptom, disease or disability.Applicator- means any device designed toconduct, transmit or transferelectromag­netic energy from a microwave diathermyunit to a patient undergoing treatment.Contro/means any control used during op­ertion of a microwave diathermy unit whichaffects the microwave radiation· emitted bythe applicator.Health professional means a registered per­son who has satisfactorily completed an ap­propriate course of training approved bythe relevant registration board and the State/Territory health authority.User means the person having administra­tive responsibility for ·use of·a particularmicrowave diathermy unit. This.person.shallbe the owner or hirer of the unit or hisagent or, if. the unit is owned or hired byan .institution .or organization, the agent ofthat body.Operator means the health professionalgiven the responsibility, by the user, to treatthe patient using .a microwave diathermyunit.Shall indicates that the particular require­ment is considered necessary to ensure pro­tection from radiation.Should indicates a procedure or precautionwhich is to be applied, whenever practica­ble, in the interests·of minimizing radiationhazards.

Hazards of ffigh Level Exposure to Micro­wave RadiationBurns

These may result as a consequence ofexcessive irradiances or may he due to pref..erential absorption of microwave radiation(as in the case of a wet dressing over awound) or to red.ucedheat dissipation mech­anisms (as in the case· of the subcutaneousfat layer). .In some cases deep tissue andorgan damage may ensue.

Ocular effectsLens opacities maybe induced by micro­

wave radiation..Single exposure to intense(> 100 mW /cm~ electromagnetic radiationat 2450 MHz for an hour or longer hasresulted in cataract formation inexperi­mental animals. The power density in thetherapeutic beam is of a similar level, butthe treatment time is generally somewhatshorter. However, repeated direct irradia­tion of the eye at such levels and for suchtreatment times does approach the power-

time threshold required for cataract pro­duction. Goggles do not offer reliable pro­tection.

Effects on the GonadsExposure to microwave .radiation may in·

crease the temperature of the testes to thepoint where temporary sterility is induced.Very .high specific absorption rates maycause permanent damage. The ovaries mayalso be at risk.

Teratogenic EffectsAbnormalities in offspring have beenre­

ported in several animal species after ex­posure to intense microwave radiation. In­tense fields resulting in significanttemperature increase of the foetus couldresult in teratogenic effects in humans.

Examination and ·InterviewMicrowave treatment shall not be admin­

istered unless prescribed by a health profes­sional .(as previously defined). At the ex­amination .and interview, when treatment isbeing prescribed, the health professionalshall determine the suitability of the patientfor treatment. This.should not be prescribedif:- The patient does not understand the

potential risks,- the patient is not able to co-operate with

the operator in maintaining the properposition and in reporting the presenceofa heating sensation which is the onlyindication of an adequate or excessivedose.

- the patient does not have normal sen­sation ·in the treatment area,

- the patient has metallic implants withinthe treatment area,

- the patient is pregnant,- the patient wears apacem,aker,- the patient has undergone ionizingra-

diation therapy to the treatment area inthe three months prior to the diathermybeing administered, as skin sensation andblood circulation may be diminished,

;,- there is evidence .or known history ofvascular insufficiency,

- the patient has any evidence of cancer,unless the microwave treatment is car­riedout as partofa hyperthermia treat­ment regime. (The metastasis of a can­cerous growth may be accelerated byamoderate increase in temperature,suchas .can be caused by a microwave treat­ment not specifically intended to treat amalignancy.),

- there are open wounds,haemorrhage,ischaemic tissue, tuberculous joints, oracute infections within· the treatmentarea.

In the cases where the health professional,after due risk/benefit consideration,sees itnecessary to prescribe >microwave diathermy

The Australian Journal of Physiotherapy. Vol. 33, No. 3)1987 159

The Safe use of Microwave and Shortwave

treatment outside the guidelines given above,adequate advice shall be given to the patient,to the user and to the operator ofthe micro,,­wave diathermy unit.

The head shall not be directly irradiatedas there isa significant· risk of irradiatingthe eyes. Most applicators are notsuffi,.ciently directional to restrict irradiation tothe targeted area. Microwave irradiation ofthe head may only be carried <out as partof acaAcer therapy.

User ResponsibilitiesThe user shall ensure, by.administrative

controls or otherwise, that:- the microwave apparatus complies with

all relevant Australian Standards and ismaintained .inaccordance with the reI,.evant State requirements,

- the unit is operated only by healthprofessionals,

- the unit operator is not exposed to aradiation level exceeding the standardfor ·occupational exposure specified bythe appropriate .authority,

- the general public (including waiting pa­tients, receptionist etc.) is not exp,osedtoa radiation level exceeding \hatrecommended by the appropriate au­thority,

- a range of applicators suitable for treat­ing different areas of the body is avail,,­able (the use of modern applicatorswhich reduce scattered radiation andconcentrate the energy to the treatmentarea is encouraged),

-"- a visibleandloraudibl~ signal is in­stalled, to indicate that the unit is op­erating,

- the unit is not. the cause of electric in­terference with other equipment (Thismay require the use of a screened.cubicleand a.mains ruter.),

- non metallic chairs andlor beds areavailable to patients undergoing micro­wave diathermy treatments.

TreatmentBefore administering the treatment the

operator shall:-"-ensure that the thermal sensitivity of the

patients is not impaired by analgesics,- ensure that the patient has removed all

metallic objects (rings, watches metalrimmed glasses, etc.) from the treatmentarea,

-ensure that the treatment area is notcovered bya wet dressing or adhesivetape,

-"- remove bandages or clothing from thetreatment area,

-"- ensure that the skin is dry,- ensure that if the patient is wearing a

hearing aid, .it is. removed,-"-ask the patient to immediately report any

symptoms experienced during the treat-

ment except' 'a mild, comfortablewarmth",

-"-ensure that the testes are not .directlyirradiated and that care is taken to min­imize indirect ·irradiation,

-ensure that the coaxial cable is correctlyconnected to both the machine .and theapplicator,

- .not rest the applicator or cable over metalsurfaces,

-align the·applicator. accurately to ensurean appropriate pattern of heating,

- direct the applicator awayfromthe unit'scontrols,

- use.care in.handling the applicator (dam­age may result in an alteration of itsdirectional properties),

- ensure that the chair or other patientsupport is not metallic.

After activating the unit the operatorshall:- remain outside the field of emission of

microwaves and at least 2 metres fromthe patient,

- not leave the patient alone in the roomduring .the treatment,

- ensure that the patient maintains the cor­rect position and remains co-operative,

- interrupt the treatment if perspirationappears on· the patient'sskin,

- not allow the patient to touch the unit,- ensure that no other person is in the

vicinity of the unit or of the applicatorduring the treatment, in accordance withthe administrative controls establishedby the user.

AppendixB

Code of Practice for the SafeUse of Shortwave*

(Radiofrequency) DiathermyUnits (1985)

IntroductionThe therapeutic use of heat produced in

deep tissue ·by<electromagnetic radiation ab"­sorbed ·in .the body is called diathermy. Theheat increases the flow of blood in the tis­sues through dilation of the blood vessels.This in tum increases capillary pressure,cellular membrane permeability, and met­abolic rate, .causing a more rapid transferof nutrients from the blood across cellmem­branes. These actions may reduce pain andpromote quicker healing~

• Reproduced by courtesy of the National Health andMedical· Research Council.

A shortwave diathermy unit is a devicedesigned to generate radiofrequency radia­tionand transfer it, via cables andelec­trodes, to theare~ to be treated. The unitscan be operated in either a continuous waveor pulsed mode, but both produce heat indeep tissue. Two basic types of electrodes(applicators) are in use, the capacitor typeand the inductor type. Inthe first case tissueheating is basically due to the radiofre­quency electric field, while for the inductiveelectrodes .(coils), .heating occurs by a com­bination of electric field effects and currentsinduced in the tissue by a magnetic field,the heating profile of the two mechanismsis somewhat different.

These devices are capable of generatinga sufficiently .high level of radiation thatthere maybe cause for concern for thesafety of the gonads and, in the case ofpregnant patients, the foetus. Improper useof the machine may result in burns andlorscalds and deep ·tissue or organ damage.Care must also be taken to avoid subjectingthe operatorand/or the public to radiationlevels exceeding those prescribed in the Aus­tralian standard AS 2772 (maximum expo­sure levels· - radio-frequency radiation ­300kHz to 300 GHz). Itmust be noted thatthe level of radiation present in the vicinityof a diathermy unit may be increased bythe presence of nearby metallic objects orother units or by reflection from the wall.

Care must be taken to ensure that theshortwave radiation .does not cause inter­ferencewith other equipment.

This Code sets down appropriate rulesand procedures to avoidexcessiveand/orunnecessary exposure to shortwave radia·tion but should be read in conjunction withanyState/Territory regulations coveringtheir use.

DefinitionsShortwave diathermy unit means a·device

using electromagnetic energy in the short­wave frequency range (3-30 MHz) fortherapeutic purposes. The unit includes elec­trodes, the shortwavegenerator,and allassociated electronics, controls andenclo­sures. In Australia the only approved fre­quency for shortwave diathermy is 27.12MHz.Treatment means the use ofa.shortwavediathermy unit ana human being to treata symptom, disease or disability.Applicator means any device designed toconduct, transmit or transfer electromag"­netic energy from a shortwave diathermyunit to a patient undergoing treatment.Control means any control used during ap­emon of a shortwave diathermy unit whichaffects the radiation emitted by theappli­cator.Health professional means a registered per­son who has satisfactorily completed an .ap-

1'60 The Australian. Journal of Physiotherapy. Vol. 33, No. 3,1987

The Safe use of Microwave and Shortwave

propriate course of training approved bythe relevant registration board and the State/Territory health authority.User means the person having administra..tive responsibility for use of a particularshortwave diathermy unit. This person shallbe the owner or hirer of the unit or hisagent or, if the unit is.owned or hired byan instttution or .organization, the agent ofthat bod¥.Operator means the health professionalgiven the responsibility, by the user,· to treatthe patient using a shortwave diathermy unit.Shall indicates that the particular require­ment .is considered necessary to ensure pro..tection from radiation.Should indicates a procedure or precautionwhich is to be applied, whenever practica­ble, in the interests of minimizing radiationhazards.

Hazards of Higb Level Exposure to Micro­wave RadiationBurns

These may result as a consequence ofexcessive exposures or may be due to non­uniform heating of different tissue layer& orto reduced heat dissipation mechanisms (asin the case of the subcutaneous fat layer).In some cases deep tissue and organ damagemay ensue because heating is induced at adepth where thermal sensation is reduced.

Teratogenic EffectsAbnormalities in offspring have been re­

ported in several animal species after ex­posure to intense shortwave radiation.Intense fields resulting in significant tem­perature increase of the foetus could resultin teratogenic effects in humans.

Effects on the GonadsExposure to shortwave radiation may in­

crease the temperature of the testes to thepoint where temporary·sterility is induced.Very high specific absorption rates maycause permanent damage. The ovaries mayalso be at risk.

Examination and InterviewShortwave treatment shall not be admin­

istered unless prescribed by a health profes­sional (as previously defined). At the ex­amination and interview, when treatment is _being prescribed, the health professionalshall determine the suitability of the patientfor treatment. This should not be prescribedif:-Thepatient does not understand the po­

tential risks,- the 'patient is not able to co-operate with

the operator in maintaining the properposition and in reporting the presenceof a heating sensation which is the onlyindication of an adequate or excessivedose.

- the patient does not have normal sen­sation in the treatment area,

~ the patient has metallic implants withinthe treatment area,

- the· patient is pregnant,- the patient wears a pacemaker,- the patient has undergone ionizing ra"

diation therapy to the treatment area inthe three months prior to the diathermybeing administered, as skin sensation andblood circulation maybe diminished,

- there is evidence or known history ofvascular insuffiCiency in the treatmentarea,

- the patient has any evidence of cancer,unless the shortwave treatment is carriedollt.as part of a hyperthermia treatmentregime. (The metastasis of a cancerousgrowth may be accelerated by a mod­erate increase in temperature, such ascan be caused by a shortwave treatmentnot specifically intended to treat a ma­lignancy.),

- there are open wounds, haemorrhage,ischaemic tissue, tuberculous joints, oracute infections within the treatmentarea.

In the cases where the clinician, ·after duerisk/benefit consideration, deems it neces­sary to prescribe shortwave diathermy treat­ment outside the guidelines given above,adequate advice shall be given to the patient,to the user and to the operator of the short­wave diathermy unit.

User ResponsibilitiesThe user shall ensure, by administrative

control or otherwise, that:- the shortwave diathermy unit complies

with all relevant Australian Standardsand is maintained in accordance withthe relevant State requirements,

- the unit is operated only by healthprofessionals,

- the unit operator is not exposed toaradiation level exceeding the standardfor occupational exposure specified bythe appropriate authority,

- the general public (including waitingpa­tients, receptionist etc.) is not exposedtoa radiation level exceeding thatrecommended by the appropriate au­thority,

- a range of applicators suitable for treat­ing different areas of the body is avail­able,

-a visibleand/or audible signal is in­stalled, to indicate that the unit isop­erating,

- the unit is not the cause of electric in­terferencewith other equipment ·(Thismay require the use of a screened cubicleand a mains filter.),

-non metallic chairs and/or beds areavailable to patients undergoing short­wave diathermy treatments.

TreatmentBefore administering the treatment the

operator shall:---ensure that the thermal sensitivity of the

patient is not impaired. by analgesics,--- ensure that the .patient has removed all

metallic objects (rings, watches, metalrimmed glasses, etc.) from the treatmentarea.

- remove bandages or clothing from thetreatment area,

- ensure that the skin is dry,- ensure that if the patient is wearing a

hearing aid, it is removed,- ask the patientto report immediately any

symptoms experienced during' treatmentexcept "a mild, comfortable warmth",

-ensure that the cables are correctly con­nected to both the machine and the ap­plicator,

- not rest the applicator or cables overmetal .surfaces,

- align the applicator accurately to ensurean appropriate pattern of heating,

- ensure that the testes are not directlyirradiated and that care is taken to min­imize indirect irradiation,

-ensure that the cables leading to the ap­plicatorare not placed in the vicinity ofthe patient's non targeted tissue,

-ensure that the chair or other patientsupport is not metallic and that otherlarge metallic objects are kept at leastthree metres from the electrodesandca­bles.

After activating the unit the operatorshall:- remain at least .1 m from the electrodes

and 0.5 m from the cables during treat­ment,

- ensurethat the patientmainta,ins the cor-"rectposition and remains co~operative,

- not leave the patient during the .treat­ment,unless the patient has been sup­plied with an emergency cut-off switchand the patient is reliable,

- not· allow the patient to touch the unit,- ensure .that no other person is in .the

vicinity of the unit or of the applicatorduring the treatment, in accordance withthe administrative controls establishedby the user.

Appendix C

Advisory AuthoritiesAustralia:Australian Capital TerritoryConsultant, Radiation ·SafetyACT Health AuthorityPO Box 825CANBERRA CITY ACT 2601Telephone: (062) 47 2899

The Australian Joumalof Physiotherapy. Vol. 33, No.3, 1987 181

The Safe use of Microwave and Shortwave

New South WalesOfficer-in-ChargeRadiation Health ServicesDepartment of HealthPOBox 163LIDCOMBE NSW2141Telephone: (02) 646 0327

Norlhern TerritoryDirectorOccup~tional and Environmental HealthNT Department of HealthPO Box 1701DARWIN NT 5794Telephone: (089)802601

QueenslandDirectorDivision of Health and Medical Physics

.Department of Health535 Wickham TerraceBRISBANE QLD 4000Telephone: (07) 224 5611

South AustraliaSenior Health PhysicistOccupational Health and Radiation ControlBranchSouth Australian Health CommissionGPO Box 1313ADELAIDE SA 5001Telephone: (08) 2183473

TasmaniaHealth PhysicistDivision of Public HealthDepartment of Health ServicesPO Box 191BHOBART TAS 7001Telephone: (002) 306421

VictoriaChief Radiation OfficerRadiation Safety SectionHealth Department of Victoria555 Collins StreetMELBOURNE VIC 3000Telephone: (03) 616 7084

Western AustraliaThe. DirectorRadiation Health BranchHealth Department of Western AustraliaVerdun Street·NEDLANDS WA 6009Telephone: (09) 389 2713

CommonwealthDirectorAustralian Radiation LaboratoryLower Plenty RoadYALLAMBIE VIC 3085Telephone: (03) 433 2211

New Zealand:The DirectorNational Radiation LaboratoryPOBox 25-009CHRISTCHURCHTelephone: Christchurch 65 059

162 The Australian Journal of PhysiQtherapy. Vol. 33, No.3, 1987