SAR patterns of external 915 MHz microwave applicators

Analysis of the results from recent clinical trials has shown that tumour size is a significant prognostic factor in eventual tumour control in patients treated with thermoradiotherapy. The critical issue appears to be the adequate coverage of hyperthermia target volume with 'therapeutic temperature'. Therefore one must choose appropriate applicators for the treatment of a given tumour. Accurate knowledge of performance characteristics of the applicators used in clinics thus becomes crucial. In an attempt to take the first step for the appropriate selection of applicators in clinics several commonly used applicators were evaluated according to their 75%, 50%, and 25% two-dimensional SAR (specific absorption rate) contours at depths of 1-3 cm. The data were subsequently approximated by rectangles. This type of information, even with its limitations, is extremely important in implementing quality assurance in hyperthermia. In this communication we will present such information, and the implications in current hyperthermia clinical trials will be discussed.