Determination of the optimal heating pattern obtained with external planar applicators used for 915 MHz microwave hyperthermia.

Knowledge of the temperature distribution in the human body in response to electromagnetic field exposure is instrumental in the assessment of the biological effects of electromagnetic waves. Such is the case of microwave hyperthermia when using external planar applicators. The goal of this paper is to determine the optimal thermal therapeutic volume (region where temperatures are in the range 42 degrees C-46 degrees C) using a F.D.T.D.-H.T.E algorithm (Finite Difference Time Domain combined with Heat Transport Equation). The variations of the blood flow coefficient as a function of temperature are taken into account. We can also determine the parameters of the bolus (thickness, temperature of the flowing water, heat exchange coefficients) which allows one to obtain this larger therapeutic volume.

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.

Non-invasive microwave multifrequency radiometry used in microwave hyperthermia for bidimensional reconstruction of temperature patterns.

Microwave radiometry, used routinely since 1984 for non-invasive temperature measurements during hyperthermia sessions for superficial tumours treatment has proven its efficiency for temperature control. From radiometric temperature measurements in two frequency ranges (around 1 and 3 GHz) and superficial (or cutaneous) temperature measurements achieved during hyperthermia sessions, a numerical method to obtain the two-dimensional thermal profile has been developed and implemented. This method is based on hyperthermia simulation from the bioheat equation, the absorbed microwave power calculation in the medium taking into account the radiative diagram of the applicator, and the calculation of radiometric temperatures. From these experimental measurements (radiometric and superficial temperatures, heating power, dielectric and thermal characteristics), a program to determine the bidimensional distribution of temperature during the hyperthermia session has been developed, tested and used during and after clinical treatments.