Nagaoka T, Kunieda E and Watanabe S. (2008). Proportion-corrected scaled voxel models for Japanese children and their application to the numerical dosimetry of specific absorption rate for frequencies from 30 MHz to 3 GHz. Phys. Med. Biol. 53:6695-6711.

The growth of wireless communication technology has led to concerns over the potential health effects, especially among children, caused by the electromagnetic waves emitted by this technology. Safety thresholds are based on the energy absorbed by the human body following exposure to radiofrequency electromagnetic fields (RF-EMFs) and are expressed as a specific absorption rate (SAR). To set safety thresholds, knowledge of SAR under all possible exposure scenarios is necessary.  However, directly measuring the SAR in a person is difficult. For this reason, computer simulations and computer models derived from high-resolution medical imaging scans of the adult human body, called voxel models, are used. To generate voxel models of children is expensive, time-consuming and fraught with ethical dilemmas and is therefore done infrequently. For these reasons, methods of scaling and re-shaping the voxel model of the adult body to that of a child have been investigated.

To develop three voxel models which match the body shapes of average Japanese children of 3, 5, and 7 years old by deforming an adult Japanese voxel model. To compare the SAR of the pediatric voxel models obtained by deformation to those obtained by simply re-scaling the adult model. To evaluate the safety standards of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) as they pertain to children.

To obtain accurate values of the body dimensions of children, 66 body parts of five children in each age category were measured. These values were then used to deform the voxel model of an adult Japanese man to fit the height, weight, and proportions of an average Japanese 3, 5, and 7 year old children. Comparable pediatric models were developed by linearly scaling the adult model to match the average height and weight of a Japanese 3, 5, and 7 year old children. SAR values were calculated using computer simulations. The strength of the electric field necessary to achieve the acceptable SAR values determined by the ICNIRP in the deformed pediatric models was compared to that of the public.

The differences in the whole-body-averaged SAR (WBA-SAR) between the deformed models and the simply scaled models were within 30% while the differences in SAR averaged over specific tissues (skin, fat, muscle) were within 10%.  Conversely, the SAR averaged over the head and neck region differed significantly between the two models.  The strength of the electric field required to produce the ICNIRP reference level for WBA-SAR exposure was much higher for the child models developed by deformation than for the public.

Interpretation and Limitations 
The simulations used in this study included various uncertainty factors which must be considered when interpreting the results. In addition, the child models may not have been representative of the wider Japanese population.

The differences in WBA-SAR between the two models are tolerable and suggest that the simply scaled models can be used to practically evaluate the WBA-SAR safety standards.  The ICNIRP safety thresholds set for the public are adequate for children, although some situations may exist where the WBA-SAR of children is above the acceptable safety limit.


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