Topic

Determination of whole-body specific absorption rates in children by means of numerical computations

Start

29.12.2006

End

30.09.2008

Project Management

IT'IS Foundation, Zurich, Switzerland

Background

Previous studies conducted by other groups revealed that children could absorb more energy compared to adults in terms of whole-body-averaged specific absorption rate (SAR) when exposed to high-frequency electromagnetic fields. Internationally recommended basic restrictions could even be exceeded in specific frequency bands. The studies performed so far used numerical body models of adults, which have been scaled down to properties of children with respect to size and weight. However, due to different proportions in bodies of adults and children and because of different tissue distributions (e.g. distribution of body fat) the uncertainty of theses results is hardly to estimate.

Objective

The study aimed at reviewing whether recommended basic restrictions are met in the frequency range between several MHz and some GHz. To overcome shortcomings of previous studies, computer simulations should use more realistic numerical models of children and adolescents rather than scaled models. As no qualified models had been available at the time of the start of the project, the models had to be developed in the first phase of the study.

Results

In the first interim report the contractor reports on the selection of the probands and the procedure of developing the CAD models from MRI scans.

The report is available as a PDF-file in German (827 KB).

The second interim report shows the body phantoms developed within the scope of the project.

The report is available as a PDF-file in German (1,177 KB).

The developed phantoms can be made available to interested parties. The right to use the phantoms is restricted to scientific purposes. Interested parties should contact the research organization (IT'IS Foundation, Zurich, Switzerland) or the BfS. Please mention the intended use.

The final report contains the results of the dosimetric simulations. They confirm that whole body absorption in children may exceed the recommended level of 0.08 W/kg when external field strengths are at reference levels. Frequencies between 1.5 and 5 GHz and around 100 MHz are affected. Basic restrictions were exceeded up to about 50%. The simulations carried out in the course of the project excel previous studies by using more realistic body models of children. The numerical uncertainty for the determination of whole-body SAR was estimated 1.2 to 1.3 dB.

Conclusions

The results confirm previous findings of others that the internationally recommended basic restriction for whole-body averaged specific absorption rate may be exceeded in children when exposed to field strengths at reference levels. The uncertainty associated with using scaled models and neglecting age-dependent dielectric properties of tissues could be reduced. However, external field strength levels that are necessary to exceed the basic restrictions do not occur at places open to the general public. All recent studies (e.g. within the German Telecommunication Programme) demonstrate that field strength levels in the vicinity of fixed transmitters like mobile phone base stations are well below the reference levels, reaching up to a few percents only. In Germany the reference levels are legal limits, set by the 26. Ordinance Implementing the Federal Immission Control Act. Field strength levels beyond the reference limits do occur in close proximity of some transmitting devices, but the field pattern are inhomogeneous and do not result in exposure situations as discussed within the course of this project. Restrictions on partial body exposure are more feasible radiation protective measure in situations like this. For that reason the results of the project do not imply any radiation protection problem for the general public at the present time. However, they reveal an inconsistency between the basic restrictions and the reference levels. ICNIRP has already provided comments on the issue [1], saying that the new dosimetric results are negligible compared to the large reduction factor of 50 (5,000%) between the basic restrictions and the reference levels. No comments of other international bodies are available at present. In Germany the new results will be discussed in the course of revising the 26. Ordinance. Further studies using models with different geometries (e.g. different BMI) and with different postures seem necessary for consolidation of the results e.g. with respect to the frequencies affected.

[1] The International Commission on Non-Ionizing Radiation Protection, "ICNIRP STATEMENT ON THE "GUIDELINES FOR LIMITING EXPOSURE TO TIME-VARYING ELECTRIC, MAGNETIC, AND ELECTROMAGNETIC FIELDS (UP TO 300 GHz)"," Health Physics, vol. 97, pp. 257-258, Sep 2009.