RF Exposure Assessment Within Interphone

Abstract

TS4-02 Abstract: Within the framework of the INTERPHONE Study, much work has gone into the development of radiofrequency (RF) exposure gradients and the estimation of associated uncertainties for the different head and neck tissues included in the case–control studies. Absorption of RF energy in the tissue volume of interest during a relevant time period is being taken as the main exposure quantity to be evaluated and allows for combining exposures at different frequencies and to different signal characteristics, eg, pulsed and continuous radio emissions. Specific absorption rate (SAR) of energy is a quantity that is routinely measured by mobile phone manufacturers to ensure compliance of their products with safety requirements. The testing involves the manipulation of a small field probe inside a phantom head shell filled with tissue-equivalent liquid while the phone is mounted in a defined position and radiates at its maximum power. In the case of compliance testing, the objective is to define the maximum average SAR occurring in any 10-g cube. However, for the purposes of INTERPHONE, SAR can then be integrated over any tissue volume of interest such as a region where a tumor was initiated and over a relevant time period. Different mobile phones produce different distributions of SAR inside the head; and INTERPHONE has put considerable effort into trying to group phones into a small number of categories that produce similar distributions based on their external observable characteristics and frequency band. Generic distributions have been developed to represent each of these classes so the SAR at a defined tumor location can be assessed by a lookup table. The output power of modern mobile phones can vary during a call, and this offers the potential for the environment in which a phone is used to influence its average output power and hence exposure. INTERPHONE has used a combination of software-modified phones (SMPs) and information from network operators to gather data on output power for a range of conditions such as indoor/outdoor, moving/stationary, urban/rural, different countries, and different network operators. There is also a need to consider whether there are any historical factors causing exposure to have changed during the period of exposure of the subject such as the move from analog to digital technology, the introduction of variable output powers, and the reducing size of mobile phones. Key dates for technologic changes influencing exposure have been collected for the network subscribed to as well as changes in the model of phone being used. In summary, the main information sources INTERPHONE is using to develop exposure indices for a particular case/control tumor are: 1. The initiation location, which is defined by neuroradiologists through an agreed reporting framework; 2. A database of generic SAR distributions from which the appropriate distribution is selected based on the phone make/model being used; 3. A database of generic phone output power distributions from which an applicable distribution is selected based on the call environment; and, 4. Data on the use of the mobile phone reported through a questionnaire.