L. Dubois

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.

Complete three-dimensional modeling of new microstrip-microslot applicators for microwave hyperthermia using the FDTD method

Describes a complete 3D modeling using the finite difference time domain (FDTD) method of a new generation of external applicators for microwave hyperthermia used at either at 434 MHz or 915 MHz without any modifications. With this new model, it is possible to obtain theoretical results concerning the variations of the reflection coefficient as a function of frequency, the power deposition inside the heated lossy tissues and the heating patterns. Experimental electromagnetic and thermal characteristics are presented and compared with the theoretical results obtained with the 3D method. >

915 MHz microwave interstitial hyperthermia. Part I: Theoretical and experimental aspects with temperature control by multifrequency radiometry

Microwave interstitial hyperthermia now plays an increasing part in the various hyperthermia techniques used in cancer treatment. This paper will present the design, construction and theoretical as well as experimental study of miniature coaxial antennas designed to heat tumours of various volumes and sizes. Monitoring temperature using multifrequency radiometry during hyperthermia stems naturally from the very design of these antennas. Experiments on phantoms, animals and patients in phase I clinical assessment have demonstrated that microwave interstitial hyperthermia can be achieved with temperature control and monitoring by microwave radiometry.

915 MHz microwave interstitial hyperthermia. Part II: Array of phase-monitored antennas

In order to heat the whole volume of a tumour by microwave interstitial hyperthermia it is necessary to use an antenna array. The antenna modelization and the numerical solution of the bidimensional bioheat transfer equation allow determination of temperature evolution during a heating session. The calculations are taken for four antennas fed in phase and the theory is then proven by experiments on gel and on patients. Results are presented on cross-section heating patterns and their time evolution. Temperature distribution is calculated when feeding one antenna by a feeding current out of phase with the other currents. The phase difference value is optimized and it is then demonstrated that the heated volume is increased by successively feeding each antenna with an out-of-phase current. The time taken to feed each antenna one after the other is optimized.

Modeling of planar applicators for microwave thermotherapy

In order to improve the external applicators used for microwave thermotherapy controlled by microwave radiometry in medical applications, we propose specific planar applicators developed for heating: either annular ones to be used at the frequency equal to 915 MHz or in the shape of a horseshoe (short-circuited ring) for 434 MHz. The final goal of this paper is the realization of a honeycomb network for the treatment of larger areas and greater volumes.

Microwave Interstitial Hyperthermia System Monitored by Microwave Radiometry (HIMCAR) and Dosimetry by Heating Pattern Remote Sensing

A complete microwave intersitial hyperthermia system with temperature control by microwave radiometry is described. The designed antennas and all their characteristics for microwave heating and radiometry are presented and taken into account in the softwares of temperature control and heating pattern reconstruction. The complete system and its using are then detailed, and its possibilites are shown through a few hyperthermia sessions.

Radiometric sensor for temperature control of food processing

This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented.

Thermal profile reconstruction in the steady state during microwave hyperthermia based on microwave radiometry measurements: bidimensional aspects

A method for bidimensional thermal profile reconstruction in the steady state during microwave hyperthermia has been developed. It is based on experimental radiometric measurements taken during the heating session. Two numerical programs have been developed: the first, which is based on the bioheat equation, gives a bidimensional thermal profile in the multilayered inhomogeneous medium; the second calculates the radiometric temperatures corresponding to this thermal profile. The two programs are combined in an optimization algorithm that is used to deduce the bidimensional thermal profile, accounting for the experimental radiometric temperatures. Comparisons between theory and experiments on phantoms, animals, and more recently on patients have given good results.<<ETX>>

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 42degC-46degC) 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.

Computation of the Electromagnetic Field with an Improved 2D FDTD Algorithm When Using Planar Applicators in Microwave Hyperthermia

In this paper, the electromagnetic field in biological tissues during microwave hyperthermia is computed by using an algorithm combining the SDA and the FDTD methods. The planar microstrip-microslot applicators as well as the surrounding heterogeneous tissues are seen to be guided structures where all electromagnetic fields are computed. Measured and computed results show a good agreement.