Life-Time Dosimetric Assessment for Mice and Rats Exposed in Reverberation Chambers for the Two-Year NTP Cancer Bioassay Study on Cell Phone Radiation

Yijian Gong, Myles H. Capstick, Sven Kuehn, Perry F. Wilson, John M. Ladbury, Galen Koepke, David L. McCormick, Ronald L. Melnick, and Niels Kuster, IEEE Transactions on Electromagnetic Compatibility, online 17 March 2017, doi: 10.1109/TEMC.2017.2665039

The main objective of this paper is to present the detailed life-time dosimetry analysis for rodents exposed in the reverberation exposure system designed for the two-year cancer bioassay study conducted by the National Toxicology Program (NTP) of the National Institute of Environmental Health Sciences (NIEHS). The study required the well-controlled and characterized exposure of individually housed, unrestrained mice at 1900 MHz and rats at 900 MHz, frequencies chosen to give the best uniformity exposure of organs and tissues. The whole-body specific absorption rate (SAR), the peak spatial SAR, and the organ-specific SAR as well as the uncertainty and variation due to the exposure environment, differences in the growth rates, and animal posture were assessed. Compared to the whole-body SAR, the average exposure of the high-water-content tissues (blood, heart, and lung) were higher by +4 dB, while the low-loss tissues (bone and fat) were less by −9 dB. The maximum uncertainty over the exposure period for the SAR was estimated to be <49% (k = 2) for the rodents, whereas the relative uncertainty between the exposure groups was <14% (k = 1). The instantaneous variation (averaged over 1 min) was <13% (k = 1), which is small compared to other long-term exposure research projects. These detailed dosimetric results empower comparison with other studies and provide a reference for studies of long-term biological effects of exposure.

The scientific and technical impact of the study can be summarized as:

• Detailed life-time dosimetry (2-year averaged exposure including variation and uncertainty for peak spatial and whole-body SAR as well as organ-averaged SAR values) is provided for the NIEHS NTP study to empower detailed analysis of the results and enable comparisons with past and future studies;
• The dosimetry covers for the first time the effects of a number of rodent postures on the electromagnetic coupling and SAR distributions;
• The numerical dosimetry was extensively validated by means of experiments performed with physical phantoms.

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