Thursday, November 20, 2014

The structure of the head affects the amount of cell phone radiation absorbed in specific brain locations

The structure of the head affects the amount of cell phone radiation absorbed in specific brain locations

My comments:  This paper identifies yet another problem with using a model of a single head, Specific Anthropomorphic Mannequin (SAM), to certify cell phones. The paper examines the specific absorption rate (SAR) using 20 different different head models that were based upon real individual heads. The authors find that the SAR in specific brain locations varies considerably depending upon the structure of the head. Since the official SAR tests use a single head (SAM), the results from the official test are not generalizable to the population. Thus, many people are likely to experience hotspots in their brain where the SAR exceeds the legal limit.


Impact of head morphology on local brain specific absorption rate from exposure to mobile phone radiation

Adibzadeh F, Bakker JF, Paulides MM, Verhaart RF, van Rhoon GC. Impact of head morphology on local brain specific absorption rate from exposure to mobile phone radiation. Bioelectromagnetics 9999:1-11, (2014). 2014 Nov 15. doi: 10.1002/bem.21885. [Epub ahead of print]


Among various possible health effects of mobile phone radiation, the risk of inducing cancer has the strongest interest of laymen and health organizations. Recently, the Interphone epidemiological study investigated the association between the estimated Radio Frequency (RF) dose from mobile phones and the risk of developing a brain tumor. Their dosimetric analysis included over 100 phone models but only two homogeneous head phantoms. So, the potential impact of individual morphological features on global and local RF absorption in the brain was not investigated.

In this study, we performed detailed dosimetric simulations for 20 head models and quantified the variation of RF dose in different brain regions as a function of head morphology. Head models were exposed to RF fields from generic mobile phones at 835 and 1900 MHz in the "tilted" and "cheek" positions. To evaluate the local RF dose variation, we used and compared two different post-processing methods, that is, averaging specific absorption rate (SAR) over Talairach regions and over sixteen predefined 1 cm3 cube-shaped field-sensors. The results show that the variation in the averaged SAR among the heads can reach up to 16.4 dB at a 1 cmcube inside the brain (field-sensor method) and alternatively up to 15.8 dB in the medulla region (Talairach method). In conclusion, we show head morphology as an important uncertainty source for dosimetric studies of mobile phones. Therefore, any dosimetric analysis dealing with RF dose at a specific region in the brain (e.g., tumor risk analysis) should be based upon real morphology.
The main objective of our study was to investigate the variation in averaged specific absorption rate (SAR) in specific brain-regions due to morphological changes, that is, changes in head size and shape.

In this study, we investigated the variation of local power absorption in the brain caused by morphological changes in 20 head models. We used two different evaluation methods and found that the variation of the averaged SAR in specific brain regions can reach up to 15.8 dB in the medulla region (Talairach method) and up to 16.4 dB in a 1 cm3 cube (field-sensor method). This large variation is due to the fact that, in different heads, the distance from the source (mobile phone antenna) to that specific brain region is different, that is, although the equivalent regions are in relatively the same positions in all brains, their absolute distances from the source are different.

... three of the four sensors with the maximum variations (Table 2: sensors 1, 9, and 10) are located in the areas in which brain tumors are most frequently found, that is, the frontal and temporal lobes. 

... the variations in morphology lead to larger differences in SAR at a higher frequency. This is caused by the fact that the smaller penetration depth at a higher frequency leads to a lower absorption in the deeper regions of the brain, and consequently to less uniform exposure of the brain.

To be able to evaluate the potential impact of our results on the Interphone study, we must apply the same restrictions as in the Interphone study ... individual morphological features, even in a restricted population, can lead up to about 12 dB variations in the RF dose absorbed at the tumor locations.

... our study had a number of limitations. First, the sample of 20 selected head models is not representative for the general population ... Second ... the brain tissues were not segmented in this study, that is, the brain was considered as a homogeneous tissue ... Third, the phone model which was used in this study was generic and simplistic ... Although a modern phone will have a different emission pattern than the generic mobile phone used in this study, this study shows that the resulting SAR distribution in the head is strongly dependent on the precise morphology of the head. 

Differences in head morphological properties caused up to 16.4 dB variation in the averaged SAR in specific brain regions between 20 head models (Sample: 13 males and 7 females aged between 36 and 76 years) and 11.8 dB limited to the Interphone's restrictions (sub-sample: four males aged between 65 and 69 years). Thus, estimation of local RF averaged SAR in the brain on the basis of generic phantoms and not on the real morphology is subject to a considerable variability and therefore head morphology should be taken into account for estimation of cumulative RF dose in the brain. The extent of this variability depends on the exposure setup (mobile phone frequency and position) and on the size and position of the brain region in question.

Joel M. Moskowitz, Ph.D.
Director, Center for Family and Community Health
School of Public Health, University of California, Berkeley

Electromagnetic Radiation Safety

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