Estimation of RF energy absorbed in the brain from mobile phones in the Interphone Study

Abstract

Objectives: The objective of this study was to develop an estimate of a radio frequency (RF) dose as the amount of mobile phone RF energy absorbed at the location of a brain tumour, for use in the Interphone Epidemiological Study.

Methods: We systematically evaluated and quantified all the main parameters thought to influence the amount of specific RF energy absorbed in the brain from mobile telephone use. For this, we identified the likely important determinants of RF specific energy absorption rate during protocol and questionnaire design, we collected information from study subjects, network operators and laboratories involved in specific energy absorption rate measurements and we studied potential modifiers of phone output through the use of software-modified phones. Data collected were analysed to assess the relative importance of the different factors, leading to the development of an algorithm to evaluate the total cumulative specific RF energy (in joules per kilogram), or dose, absorbed at a particular location in the brain. This algorithm was applied to Interphone Study subjects in five countries.

Results: The main determinants of total cumulative specific RF energy from mobile phones were communication system and frequency band, location in the brain and amount and duration of mobile phone use. Though there was substantial agreement between categorisation of subjects by cumulative specific RF energy and cumulative call time, misclassification was non-negligible, particularly at higher frequency bands. Factors such as adaptive power control (except in Code Division Multiple Access networks), discontinuous transmission and conditions of phone use were found to have a relatively minor influence on total cumulative specific RF energy.

Conclusions: While amount and duration of use are important determinants of RF dose in the brain, their impact can be substantially modified by communication system, frequency band and location in the brain. It is important to take these into account in analyses of risk of brain tumours from RF exposure from mobile phones.

Figure 1

Combining the information collected in the Interphone study into an RF dose estimate

Figure 2

Surface and axial views of 1 cm3 SAR (W/kg) distributions in the GRIDMASTER brain at 800-900 MHz and 1800 MHz respectively, for a phone held on the right side (the colour scale used in all views is the same)

Figure 3

Distribution of estimated CSE (in J/kg) at the origin of the tumour by mobile phone communication system and frequency band. (Glioma study subjects 5 Interphone countries. For controls, location of tumour is taken to be the location of the tumour of the case to which they are matched). AMPS: Advanced Mobile Phone System; D-AMPS: Digital AMPS; CDMA: code division multiple access; GSM: Global System for Mobile. Numbers beside CDMA and GSM indicate the main frequency band (see Appendix 1 for details of the communication systems).