Quantitative evaluation of 2 x 2 arrays of Lucite cone applicators in flat layered phantoms using Gaussian-beam-predicted and thermographically measured SAR distributions.

SAR distributions from four different E-field-orientated 2 x 2 arrays of incoherently driven Lucite cone applicators (LCAs) were investigated. The LCAs operated at 433 MHz with an aperture of 10.5 cm x 10.5 cm each. Two techniques were used to obtain SAR distributions in flat layered phantoms: Gaussian beam (GB) predictions and thermographical (TG) imaging. The GB predictions showed that the effective field size of the different array configurations varied by up to 3%. The TG-measured SAR distribution showed significant deviations from the GB-predicted SAR distributions (maximum 34.6%). The difference between GB-predicted and TG-measured SAR levels (averaged per 10% GB-predicted SAR intervals) equalled less than 11.3% for the parallel E-field orientated array and respectively 15.1% for the clockwise-orientated array. When antennae in the clockwise-orientated array were more widely spread (array aperture 23 cm x 23 cm) in order to diminish their mutual interactions, these differences decreased to 12.4%. However, the overall difference within the 50% SAR or higher range decreased from 14% to 9%. The results lead us to conclude that LCAs can be used clinically and their antenna interactions are not considered to be a problem under clinical conditions.