WHO International EMF Project. International Advisory Committee Meeting June 2009

Transcription

1 WHO International EMF Project International Advisory Committee Meeting June 2009 National Collaborating Institute Report Radiation Protection Division of the UK Health Protection Agency The Health Protection Agency (HPA) was formed in 2003 and brought together several organisations in order to provide an integrated approach to protecting UK public health. The HPA has a large network of approximately 3000 staff based at three major centres, and regionally and locally throughout England. There is a small central office based in London. The Agency works closely with locally based colleagues employed within the devolved administrations of Wales, Scotland and Northern Ireland. The Centre for Infections at Colindale is the base for communicable disease surveillance and specialist microbiology. The Centre for Radiation, Chemical and Environmental Hazards (CRCE), is based at Chilton and the Centre for Emergency Preparedness and Response, focusing on applied microbiological research and emergency response, is based at Porton Down. On 1 April 2005 the National Radiological Protection Board merged with the Health Protection Agency (HPA) forming its Radiation Protection Division (RPD). Together with the Chemical Hazards and Poisons Division of HPA it forms the Agency s Centre for Radiation, Chemical and Environmental Hazards (CRCE). RPD carries out the Health Protection Agency s work on ionising and non-ionising radiations. It undertakes research to advance knowledge about protection from the risks of these radiations; provides laboratory and technical services; runs training courses; provides expert information and has a significant advisory role in the UK. Patient and Volunteer Exposures in MRI New HPA advice was published in August 2008 on the protection of patients and volunteers from the static magnetic fields, switched gradient (time-varying) magnetic fields, RF fields and acoustic noise associated with MRI procedures [1]. Advances in technology now mean that MRI can be routinely used for diagnosis in most areas of the body and in most clinical specialities. Furthermore an increasing number of scanners in clinical use produce static fields of magnetic flux density 3 tesla (T). The new advice was produced by the HPA MRI Patients and Volunteers Group (MPEG) comprising staff from the HPA s Radiation Protection Division (RPD) and external experts in the field of MRI technology and its applications. The Group s main conclusion was that that the ICNIRP MRI exposure limits for static, switched gradient, and RF fields are broadly appropriate. However, somewhat higher exposure to static magnetic fields than those recommended by ICNIRP should be allowed, but only under carefully controlled exposure conditions. The new advice recognises the clear benefits to individual patients undergoing MRI examinations and more generally, through research involving volunteer exposures, to increasing medical knowledge for the benefit of all. It also sets out recommendations on best practice and further research needs. The advice is on the HPA website.

2 UK ELF stakeholder group SAGE is the Stakeholder Advisory Group on ELF EMFs which has been set up by the Department of Health to explore the implications and make practical recommendations for a precautionary approach to power frequency electric and magnetic fields. SAGE has representation from public concern groups as well as from the power supply industry, government departments and the Health Protection Agency. SAGE published its first interim report on 27 April The report considered a wide range of possible health effects, and mitigation options such as the 'corridor option', in which no development would not occur within a certain distance of power lines, optimal phasing of lines to reduce electric and magnetic fields, the design and promotion of low magnetic field appliances and changes in wiring practice, and provision of information in the public domain. The report is available on the SAGE website. HPA advises that precautionary measures should address the possible association with childhood leukaemia and not other more speculative health effects. HPA advises that it would be wise to err on the side of caution, but with a proportionate response. HPA supports precautionary measures that have a convincing evidence base to show that they will be successful in reducing exposure, are effective in providing reassurance to the public, and where the overall benefits outweigh the fiscal and social costs. The full advice from HPA, including responses to the range of measures identified by SAGE can be found on the HPA website: The Department of Health is considering the points HPA made on the SAGE interim report in consultation with colleagues in other areas of government. Theoretical Dosimetry Research at HPA-RPD Intercomparison of Voxel Phantoms An intercomparison of the HPA male and female models, NORMAN and NAOMI with the National Institute of Information and Communications Technology (NICT) male and female models, TARO and HANAKO has been performed [3]. Finite-Difference Time-Domain (FDTD) calculations of the whole-body SAR in these 4 phantoms were carried out at HPA, NICT and the Nagoya Institute of Technology. The exposures were for a plane wave with a vertically aligned electric field incident upon the front of the body from 30 MHz to 3 GHz under isolated conditions. As well as investigating the general differences through this frequency range, particular emphasis was placed on the assumptions of how dielectric properties are assigned to tissues (particularly skin and fat) and the consequence of using different algorithms for calculating SAR at the higher frequencies. Foetal SARs A study was performed to compare the foetal SAR in the HPA hybrid mathematical phantoms with the 26-week foetal model developed at NICT, Tokyo and the set of 13-, 26- and 38-week boundary representation models produced at Rensselaer Polytechnic Institute (RPI) [4]. FDTD calculations were performed at a resolution of 2 mm for a plane wave with a vertically aligned electric field incident upon of the body from the front, back and two sides from 20 MHz to 3 GHz under isolated conditions. The direction of irradiation was found to be important when looking at localised SAR in the foetus because of the varied postures and different positions within the uterus. These variations in the anatomy provide a way to understand the range of potential uncertainties in this type of calculation with potentially large differences in localised SAR depending on the particular model and incident field direction. A comparison of the electric field values required to produce the ICNIRP public exposure restriction of 2 W kg 1 over 10 g in the foetus for the models at 13-, 26- and 38-weeks gestation with the ICNIRP reference levels showed that the ICNIRP public reference level is still a very conservative predictor of local SAR in the foetus.

3 Spatial averaging An investigation to assess the validity and accuracy of spatial averaging when used for halfwave dipoles at frequencies between 65 MHz and 2 GHz and distances of λ/2, λ/4 and λ/8 from the body has been completed [7]. The differences between mean electric field values calculated using 10 field measurements and that of the true averaged value were ~15% in the 600 MHz to 2 GHz range. The results presented suggest that the use of modern survey equipment, which takes hundreds rather than tens of measurements, is advisable to arrive at a sufficiently accurate mean field value. Whole-body averaged and peak localised SAR values, normalised to calculated spatially averaged fields, were calculated for the NORMAN voxel phantom. It was found that the reference levels were conservative for all whole-body SAR values, but not for localised SAR, particularly in the 1-2 GHz region when the dipole was positioned very close to the body. However, if the maximum field is used for normalisation of calculated SAR as opposed to the lower spatially averaged value, the reference levels provide a conservative estimate of the localised SAR basic restriction for all frequencies studied. Experimental Dosimetry Research at HPA-RPD UK Childhood Cancer Study (ELF) The bulk of the ELF EMF research in the EMF Dosimetry Group has been in support of the UKCCS, a large and comprehensive case-control epidemiological analysis of the possible causes of childhood cancer. Several distinct exposure-based hypotheses were assessed in the study, including childhood exposure to EMFs. The key aspects of the dosimetry work have included assistance in the design and development of appropriate exposure protocols; provision and development of instrumentation and instrument integrity check sources and the maintenance of calibration facilities; modelling and computation of exposure measures; and the training of study staff in the measurement of electric and magnetic fields. Most of the UKCCS research in this area has now been completed; however, the UKCCS Research and Steering Committee has identified EMFs as one of the continuing strategic areas of the study, and the EMF Dosimetry Group continues to contribute to the study through the execution of supplementary analyses and involvement in scientific meetings. Residential Sources Study (ELF) The Residential Sources Study published in 2007 has provided an important basis for understanding sources of elevated ELF exposure in UK homes, and this year, an analysis was completed which demonstrated the high level of exposure misclassification which arises from the use of the distance from power line exposure surrogate [9]. These research activities have provided valuable input to HPA advice, most recently in its response to the First Interim Assessment of the Stakeholders Advisory Group on ELF EMFs (SAGE), as mentioned above. Exposure to Wi-Fi in schools The Agency announced in November 2007 that it was to carry out a systematic programme of research into wireless local area networks (WLANs) and their use. The project began with a review of technical standards and existing exposure information. A review of equipment used in schools was then carried out and this led to a selection of equipment for testing (laptops and access points operating in 2.4 & 5 GHz bands). Experimental facilities have been constructed, consisting of an anechoic chamber with a positioning system that allows power density to be measured as a function of angle from a source and as a function of distance up to 2 m. Unlike previous studies, which have used a spectrum analyser and had to make compacted corrections to measure burst power, this study is using a signal analyser to measure burst power directly. Results for the field strengths and total radiated powers from laptops at 2.4 GHz will be presented at the BEMS Conference in June 2009 (next week).

4 In addition to the burst powers, the duty factors of Wi-Fi equipment during normal use are needed to assess exposures. The project is investigating various ways to acquire these data during school lesson scenarios to identify the range of values that occurs during normal use and any possible determinants associated with the type of activity. The internal electromagnetic structure of WiFi sources, in particular their antenna types and locations, is also being considered and will provide an input to computer modelling of equipment and exposed people in realistic scenarios. The results will be compared with international exposure guidelines and also with exposures from other commonly used RF sources, including mobile phones. A health risk review will be performed at the end of the project. Information about the project and HPA s position on Wi-Fi is available on the following web pages. MobiKids Mobikids is a new international case-control study that will research into the potential associations between the use of communication devices and other environmental risk factors and brain tumours in young people. Over a study period of five years, nearly 2000 young people between 10 to 24 years with brain tumours (cases) and a similar number of young people without a brain tumour (controls) will be invited to participate in the study. Support for exposure assessment will be provided by France Telecom SA and the UK Health Protection Agency and involves tasks such as identifying which factors need to be taken into account in the questionnaire design as well as performing occupational and environmental exposure assessments from extremely low frequency (ELF) magnetic fields and radio frequency (RF) EMF sources. Independent Advisory Group on Non-ionising Radiation Protection (AGNIR) Background AGNIR was set up in The terms of reference were to review work on the biological effects of non-ionising radiation relevant to human health and to advise on research priorities. The Group was reconstituted in 1999 as an independent advisory group and reported directly to the Board of NRPB; since April 2005 it reports to the sub-committee of the Board of the HPA that deals with radiation, chemical and environmental hazards. In addition to the work of the Advisory Group, subgroups address specific issues. The Advisory Group has, to date, issued twelve major reports and a number of statements. The reports have mainly covered reviews of experimental and epidemiological studies, together with exposure data relevant to assessing possible health effects from exposures to electromagnetic fields (EMFs) and ultraviolet radiation (UVR). They have been a valuable input to NRPB, and now HPA, advice and have been used in the development of UK exposure guidelines as well as being widely circulated and used by the UK Government and the devolved administrations. The ongoing programme of work of AGNIR is summarised below and it is also given on the HPA web site: Static magnetic fields Static magnetic fields are used in certain industries, high energy physics research facilities, and particularly in medicine where magnetic resonance imaging (MRI) provides exceptionally clear images of tissue that can lead to more precise diagnosis of disease or injury. There have been rapid advances in the applications of static fields and, in addition, there have been progressive increases in the strength of the fields used. In particular, in MRI, it is expected that exposures of several tesla (T) may become more common while partial body exposures can be even higher. The AGNIR published its report on Static Magnetic Fields in May

5 AGNIR concluded that there is a pressing need for a well-conducted study of mortality and cancer incidence in workers with high occupational exposures to static magnetic fields, particularly those associated with medical MRI scanners. HPA responded by setting up a scoping group to examine the feasibility of such a study and with the aim of launching it as soon as possible. A press release is available on the HPA website: Radiofrequency radiation The Independent Expert group on Mobile Phones (IEGMP) drew attention to concerns on this topic in its 2000 report and called for more research. Similar calls were raised in other countries around the same time, and also within Europe and by the WHO. The result has been a substantial programme of research supported by governments, industry and the European Union. In recognising that research would proceed apace, IEGMP recommended that a further review of the science should be carried out within three years of its own report and the AGNIR prepared such a review in At this time, many studies were in progress and, in particular, epidemiological research of mobile phone users was at an early stage. Hence, it was agreed in 2003 that the AGNIR should produce a further review of studies relevant to concerns about health for publication in a few years time. The first phase of the UK s Mobile Telecommunications and Health Research (MTHR) programme is now drawing to a close and a report on the bulk of the work has been published. The initial phases of work funded in other countries and by the EU are also largely complete, meaning that the time is right for the AGNIR to begin its review. The AGNIR has therefore been asked to perform a review of exposure to radiofrequency radiation and human health focusing particularly on those areas of the science where knowledge has been added since its last review. This work is expected to take 2-3 years and will begin this summer. Power frequency fields In 2001 the AGNIR published its most recent report on ELF Electromagnetic Fields and the Risk of Cancer. The AGNIR continues to keep under review published research related to health concerns arising from exposure to power frequency electromagnetic fields. At present there is insufficient new information to justify the development of an update to the 2001 report although this will be needed at some point in the future. Some recent EMF-related publications from HPA-RPD [1] HPA (2008). Protection of patients and volunteers undergoing MRI procedures: Advice from the Health Protection Agency. Documents of the HPA, RCE-7. (Prepared by: McKinlay AF, Bouffler SD, Broom K, Findlay RP, Mann SM, Meara J, Muirhead CR, Saunders RD, Sienkiewicz ZJ, Wainwright PR, Zhang W, Giles S, Gowland PA, Hand JW, Price DL, Maslanyj MP and Rance L. August [2] Dimbylow P J and Findlay R P. (2009) SAR Calculations in Realistic Voxel Models and their Application to Electromagnetic Field Guidelines. To be published in EMC/Kyoto Conf. Proc. [3] Dimbylow P J, Hirata A and Nagaoka T. (2008) Intercomparison of whole-body averaged SAR in European and Japanese voxel phantoms. Phys. Med. Biol [4] Dimbylow P J., Nagaoka T and Xu X G. A comparison of foetal SAR in three sets of pregnant female models. Phys. Med. Biol. in press (2009) [5] Findlay R P and Dimbylow P J. (2008) SAR calculations in a human voxel phantom under exposure conditions where the incident electromagnetic field is reflected from a ground plane. Bioelectromagnetics Society Annual Conference, San Diego.

6 [6] Findlay R P and Dimbylow P J. (2009) Problems with Electromagnetic Guidelines for Scaled Child Voxel Models in Various Postures between 10 MHz and 3 GHz. To be published in EMC/Kyoto Conf. Proc. [7] Findlay R P and Dimbylow P J. (2009) Spatial averaging of fields from half-wave dipole antennas and corresponding SAR calculations in the NORMAN human voxel model between 65 MHz and 2 GHz. Phys. Med. Biol [8] Lophatananon A, Liu JF, Van Tongeren M, Demetriou L, Hepworth SJ, McKinney P, Mee T, Whatmough P, Dunn C, Broad L, Maslanyj M, Allen SG, Bowman JD, Yost MG, Richardson L, Hours M, Muir K. Occupational exposure to extremely low frequency magnetic fields and the risk of glioma, meningioma and acoustic neuroma; a UK case control study. American Journal of Epidemiology (in press). [9] Maslanyj MP, Simpson J, Roman E, and Schüz J (2009). Power frequency magnetic fields and risk of childhood leukaemia: Misclassification of exposure from the use of the distance from power line exposure surrogate. Bioelectromagnetics, 30(3): [10] Peyman A, Gabriel C, Grant EH, Vermeeren G and Martens L, 2009, Variation of the dielectric properties of tissues with age: the effect on the values of SAR in children whenexposed to walkie talkie devices Phys. Med. Biol. 54 (2009) [11] Peyman A, Calderon C, Mann S, Khalid M, Addison D and Mee T, 2009, Evaluation of Exposure of School Children to Electromagnetic Fields from Wireless Computer Networks (Wi-Fi): Phase 1 Laboratory Measurements, Bioelectromagnetics Society s annual Meeting in Davos, June 2009 [12] Wainwright P R (2008) A parametrised planar tissue model to investigate the relationship of temperature rise, SAR and power density. 5th International Workshop on Biological Effects of Electromagnetic Fields. Sicily Sep 28-Oct Prepared by Simon Mann, Head of Physical Dosimetry Department Radiation Protection Division Health Protection Agency Chilton Oxfordshire OX11 0RQ United Kingdom simon.mann@hpa.org.uk