Biological Rationale for Setting Exposure … Rationale for Setting Exposure Guidelines for ... • used dipole or horn antenna at 450 MHz or pulsed 2450 MHz, ... base of skull,

ICNIRP-MIC INTERNATIONAL WORKSHOP

Tokyo Japan 2nd December 2016Tokyo, Japan, 2 December 2016

Biological Rationale for Setting Exposure Guidelines for

High Frequency Fieldsg q y

Zenon Sienkiewicz ICNIRP



HF fields are defined as 100 kHz to 300 GHz

<1 Hz 100 kHz 300 GHz

HF fields are defined as 100 kHz to 300 GHz

Ionising RadiationOptical Lowfrequency

High frequencyq y q y



Starting perspectiveInvestigated for > 50 years

• Many thousand studies• Many thousand studies• Much information on many endpoints

Technically challenging subject• Metrology and dosimetry complexgy y p• Large scope for artefact/errors

ICNIRP (1998) RF GuidelinesICNIRP (1998) RF Guidelines• Based on stimulation and thermal effects



Frequencies of most interest

2.45 GHz cooking, industrial, Bluetooth10-50 MHz industrial, scientific, medical uses800-2000 MHz TACS, NTACS, NTT;800 2000 MHz TACS, NTACS, NTT;

GSM, DECT, TDMA; and UMTS400 500 MHz NMT TETRA400-500 MHz NMT, TETRA



What information do we need?

Scientifically substantiated effects of exposure• Good laboratory/epidemiological practices • Defined exposure and dosimetry • Control of confounding/bias • Appropriate statistics• Independent replication• Understand interaction mechanism• Consistent with present knowledge

Sir Austin Bradford Hill



Once substantiated effects identified Need to decide

• Acceptable level of risk, if stochasticAcceptable level of risk, if stochastic– probability increases with dose without a threshold

• Health effect level, if deterministic,– severity increases with dose above a threshold

• Reduction factors to produce appropriate exposure value – variability in biological response– uncertainty in metrology or dosimetry

i d d t f ff t– size depends on type of effect – not precise, expert judgement required here



So how do we use this information?Formulate basic restrictions

• Dosimetric quantities inside the bodyDosimetric quantities inside the body• Cannot be measured directly in people• Rate of energy absorption (mass or area)• Rate of energy absorption (mass or area)• Limits on exposure

Calculate reference levelsCalculate reference levels• Readily measurable field quantities

U d f d t ti li• Used for demonstrating compliance• Not limits of exposure



Investigated consequences of exposure

Cancer Male infertility, Cancer y,reproduction and

child developmentchild development

Cardiovascular t

Nervous systemoutcomes

ydisease



Substantiated consequences of exposure

Nerve stimulation

Elevation of tissue t t d

(ICNIRP 2010)

temperature and responses to heat

ElectroporationElectroporation

Microwave hearingMicrowave hearing



Thermoregulation in RF-exposed volunteersSeries of six studies by Eleanor Adair and colleagues (1998-2005)• healthy adults, male and female, n = 7 or 6, seated in bathing suits• exposed in anechoic test chamber for 45 min low humidity constant air flowexposed in anechoic test chamber for 45 min, low humidity, constant air flow• ambient temperature of 24, 28 or 31 C• used dipole or horn antenna at 450 MHz or pulsed 2450 MHz, behind subject,

partial body exposure on head, trunk, upper arms, 6 to 15 W/kgp y p , , pp , g• used dipole in corner reflector at 100 or 220 MHz, behind subject, whole-body

exposure, 0.2 to 0.7 W/kg

Physiological parameters measured before during and after exposure• oesophageal (core) and local skin temperature• metabolic heat production• sweating rates• local skin blood flow• heart rate (in latter studies)



Summary of Adair’s resultsCompared last 10 min of 30 min acclimation period with last 10 min of exposure

Overall magnitude of responses depend on ambient temperature and SAROverall, magnitude of responses depend on ambient temperature and SAR But great variability between individual subjects

Results are mainly descriptive few statistical analysesResults are mainly descriptive, few statistical analyses • no measurable effects on metabolic heat production• small changes in body core temperature (~ 0.1 to ~ 0.3 C, peak 0.48 C)• local skin temperature increased (~1 5 to ~ 4 C) plateau reached after ~15 to 30local skin temperature increased ( 1.5 to 4 C), plateau reached after 15 to 30

min only at higher ambient temperatures• 100 and 220 MHz (resonance) produced hot spots in top of foot, front of ankle,

base of skull, back of kneebase of skull, back of knee• also skin blood flow, sweat rates increased with increasing SAR at 28 or 31 C• moderate effects on heart rate (<15% increase)

Results consistent with responses to conventional thermal stress



MRI studies with volunteersSt di h i ti t d th l ti i MRI lth h t di did tStudies have investigated thermoregulation using MRI, although some studies did not include a sham control or volunteers were not blind to exposure conditions• suggest exposures used only caused small rises in core temperature, acceptable

rises in local skin temperaturerises in local skin temperature

Kido et al (1987) • used a 1 5 T system sham had no RF just static and gradient fields• used a 1.5 T system, sham had no RF just static and gradient fields• axillar temperature measured by thermistor probe before and after exposure (17 min)

• 13 subjects exposed to head scan at 0 02 or 0 06 W/kg13 subjects exposed to head scan, at 0.02 or 0.06 W/kgno significant increase in temperatureheart rate decreased (>3 bpm) at higher SAR

• 14 subjects exposed to lumbar scan at 0.2 or 0.8 W/kgtemperature increased by 0.2 C and 0.5 Cheart rate increased (3 bpm) at higher SAR( p ) g



Boss et al (2007) • used a 3 T system sham had no RF just static and gradient fields• used a 3 T system, sham had no RF just static and gradient fields• skin temperature measured by fibre-optic sensors or IR camera for 10min

before and during exposures (6 and 4 min) • 18 subjects, exposed to 3D gradient-echo sequence and 2D fast spin-echo18 subjects, exposed to 3D gradient echo sequence and 2D fast spin echo

sequence of pelvis (WBA SAR 1.6 or 2.9 W/kg), head (1.2 or 2.5 W/kg), or knee (0.2 or 4.8 W/kg)

• mean skin temperatures all increasedp~ 1 C for pelvis~ 0.5 C for head ~ 0.3 C for knee

• no effect on heart rate or blood pressure

• “…may be regarded as safe, even in patients with cardiovascular disease.”



Mobile phone handsetsStraume et al (2005) • measured temperatures in ear and cheek by IR camera in one male • GSM 900 MHz signal at 0 21 W (~ 0 8 W/kg) or signal to load or turned off• GSM 900 MHz signal at 0.21 W (~ 0.8 W/kg) or signal to load, or turned off• after 15 and 30 min, compared to non phone side, • temperature rise of ~ 1.5 C due to insulation, ~ 0.7 C due to electrical power dissipation• no additional effects of RF



Dorn et al (2014) d t t i b i 15 l

Position of non perturbing fluoro-optical glass probes

• measured temperature using probes in 15 males• TETRA 385 MHz via antenna fixed at left ear• heating of antenna of ~ 0.2 C• non-significant temperature increases at 1.5 W/g of ~ 0.3 C• significant temperature increases at 6 W/kg of ~ 0.8 C



Lindholm et al (2011) ( )• measured temperature in ear canal and on face in 23 males, 14-15 years,

using thermistors and IR camera• GSM 902 MHz, battery/speaker removed, via coaxial cable from another

phone, 4 cm from right ear (dummy phone on left)• average SAR of 2.0 W/kg in head , 0.66 W/kg in brain• no significant increase in temperature in ear or on face• also no effect on cerebral blood flow, heart rate or mean arterial pressure



ConclusionsHealthy people are able to maintain core body temperatures very effectively and efficiently under a range of thermal loads • behaviour skin blood flow sweatingbehaviour, skin blood flow, sweating

Laboratory studies with volunteers exposed to RF fields suggest• skin temperatures may increaseskin temperatures may increase • but core body temperature is minimally increased • thermoregulatory mechanisms are working well• no adverse health effects

Overall, responses are consistent with conventional heat stress or exercise• BUT studies used small number of resting subjects • need studies with larger numbers and performing physical activity • a wider range of ambient conditions and exposures



Generalised thermoregulatory profileSweatingIncreased

skin blood flow LCT

lower critical temperature

UCT

flow

UCT upper critical temperature

TNZShivering

TNZthermoneutral zone

from Adair and Black (2003)



Generalised heat balance equation

S = M ± W ± R ± C ± K − E + RF

S is rate of heat storage (ideally, close to zero )

M is metabolic heat productionW is mechanical work by/on body

R is heat exchange via radiation C i h h i i ( ki bl d fl )C is heat exchange via convection (skin blood flow)K is heat exchange via conduction

E i h t h i ti ( ti l )E is heat exchange via evaporation (sweating, lungs)

RF is rate of absorbed RF energy (W/kg) =



Body core temperature

Average body core temperature (BCT) ~ 37 Cindividual differences 36 38 Cindividual differences 36 - 38 Ccircadian variation ± 0.5 C

Elevated BCT above average (hyperthermia)38 C h t t ( ibl h d h di i> 38 C heat stress (reversible: headache, dizziness,

increased accident rates)>40 C heat stroke (severe: unconsciousness)>40 C heat stroke (severe: unconsciousness)>43 C death



Thresholds for whole body effects

Operational threshold for heat stress is taken asOperational threshold for heat stress is taken as increase in BCT of 1 Cnot possible to specify as absolute valuenot possible to specify as absolute value

This is taken to correspond to whole body average SAR of 4 W/kgThis is taken to correspond to whole body average SAR of 4 W/kgconservative value to reflect paucity of human data



Thresholds for local effectsThreshold for thermal damage to tissues > 41 - 43 C

likelihood of damage and severity increases with timelikelihood of damage and severity increases with time Operational threshold for thermal damage is taken as 40 - 41 C

Head and trunk (includes eyes, abdomen, pelvis, thorax)( y p )limited to increase of 2 C absolute value of 40 C (assuming typical temperature of <38 C)

Testes limited to increase of 2 Cabsolute value of ~35 C (assuming typical temperature of ~33 C)absolute value of ~35 C (assuming typical temperature of ~33 C)

Extremities (includes arms & hands, legs & feet, skin, pinna)limited to increase of 4 C absolute value of 40 C (assuming typical temperature of < 36 C)



Thresholds for local effects At 100 kHz to 6 GHz, using 10 g averaging mass, heating factor of 0.2 C kg/W g

This is taken to correspond to s s a e o co espo d oLocal SAR in head and trunk of 10 W/kgLocal SAR in extremities of 20 W/kgLocal SAR in extremities of 20 W/kg

Above 6 GHz mainly skin heating use incident power densityAbove 6 GHz, mainly skin heating, use incident power densityAt 30 GHz, this is taken to correspond to

400 W/m2 averaged over 4 cm2 body surface400 W/m averaged over 4 cm body surface increases at lower frequencies, decreases at higher



Possible basic restrictions f h l b d ff tfor whole body effects

Reasonable to use a 6 min averaging time

Apply reduction factor of 10 for workersSAR of 0.4 W/kg

Apply reduction factor of 25 for the general publicSAR of 0.16 W/kg



Possible basic restrictions for local effects Reasonable to use a 6 min averaging time, 10 g averaging massFor head and trunk

Apply reduction factor of 2 for workersSAR of 5 W/kg

Apply reduction factor of 5 for the general public SAR of 2 W/kg

For extremitiesApply reduction factor of 2 for workers

SAR of 10 W/kgApply reduction factor of 5 for the general public

SAR of 4 W/kg



Possible basic restrictions for incident power density (6-300 GHz)

Reasonable to use a 6 min averaging time

Apply reduction factor of 2 for workers280 W/m2 to 140 W/m2

Apply reduction factor of 5 for the general public110 W/m2 to 56 W/m2

Averaging interval depends on frequency (from 6 min to 10 s)



Summary and conclusions Presented a logical and scientific rationale

based on local and whole body heatingy gusing other endpoints not justifiable

Provides adequate protection for workers, members of the public including children and those at particular risk

Rationale is not yet completey pmicrowave hearing effectelectroporationp



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Biological Rationale for Setting Exposure … Rationale for Setting Exposure Guidelines for ... • used dipole or horn antenna at 450 MHz or pulsed 2450 MHz, ... base of skull,