Dosimetry considerations in far field microwave exposure of mammalian cells

A circulating water bath exposure system has been designed for in vitro radiofrequency radiation (RFR) exposure studies in the 915 to 2450 MHz range. A Styrofoam float, in which 10 T-25 plastic tissue culture flasks are embedded, is rotated at approximately 20 rpm in a Plexiglas water bath at a distance beneath a rectangular horn. The continuous circular rotation of the flasks is designed to "average out" the heterogeneity present in stationary flask exposures. The rotation also serves to prevent the establishment of chemical gradients in the medium within the flasks. Several factors have been demonstrated to affect the specific absorption rate (SAR) measured in the medium in the exposed flasks. These factors include: 1) the position of the exposure flasks relative to the long axis of the antenna horn; 2) whether the flasks are exposed while stationary or in rotation; 3) the volume of the medium contained in the flask; and 4) the depth in the medium in the flask at which temperatures for SAR calculation are measured. The presence of cells in the exposure flask (as attached monolayer or cell suspension) did not result in an SAR different from that measured in the same volume of medium without cells present.