New 434 MHz interstitial hyperthermia system monitored by microwave radiometry: theoretical and experimental results

A new complete microwave interstitial hyperthermia system monitored automatically by microwave radiometry and working at 434 MHz is described in this paper. This system, which includes a new radiometer with two internal temperature references, is detailed. All its characteristics for microwave heating and radiometry are presented. The new possibilities are shown through numerous experiments on acrylamide phantom and excised tissues, which have been carried out for different antennae implantation corresponding to the clinical situation. The clinic protocol, associate to the brachytherapy, imposes the use of semi-loop catheters. Coaxial antennae, inserted in these catheters, are not, therefore, positioned in a rectilinear manner but undergo a curve. So, models based on the FDTD formalism are developed to determine the theoretical power deposition. Owing to these models, the effects of this physical motive on radiation diagrams can be taken into account. The results of the power deposition are presented for two antennae. Thermal patterns can then be determined by the solution of the bioheat-transfer equation in the steady state. Also, the comparison of the results given by the new interstitial hyperthermia system with those obtained with the previous 915 MHz one shows an improvement of the thermal performances.