SAR CHARACTERISTICS OF 3 TYPES OF CONTACT FLEXIBLE MICROSTRIP APPLICATORS FOR SUPERFICIAL HYPERTHERMIA

The Effective Field Sizes (EFS) and the Effective Heating Depths (EDH) of Contact Flexible Microstrip Applicators (CFMA), tuned at a frequen cy of 434 MHz, were determined on two fat/muscle phantoms. One phantom was box-shaped with a flat top layer of 1 cm thick artificial fat and the other one a tube of which the cross-section was elliptically shap ed (25 x 36 cm) having a fat equivalent shell of 1 cm thick. For the m uscle material a 6 g/l saline (NaCl) solution was used. On the flat re ctangular phantom, the effective field size at 1 cm depth in saline wa s measured to be 4.7 x 13.5 cm, 17.5 x 17.7 cm and 12.5 x 14.0 cm for the 1H-applicator, the 3H-applicator and the SH-applicator, respective ly. For the 3H- and the 5H-applicator, the Specific absorption rate (S AR) distribution at 1 cm depth showed a single maximum of SAR for a th in bolus, which split into two separate 'hot spots' for a thicker bolu s. The Effective Heating Depths in the phantom with a flat surface wer e of the order of that of a plane wave (approximate to 1.4 cm), wherea s a larger EHD of 2.4 cm was achieved below the 3H-applicator bent to fit the elliptical phantom. Due to the large effective field size and the 'flatness' of the SAR distribution, the applicators 3 H and 5 H ar e suitable to adequately treat large superficial tumours.