M. Chive

Microwave prostatic hyperthermia: interest of urethral and rectal applicators combination-theoretical study and animal experimental results

Microwave thermotherapy systems used for benign prostatic hyperplasia treatment generally operate with urethral or rectal applicator to deliver the microwave energy in the prostate. This technique does not allow an efficient heating of all the gland particularly in the case of large adenoma or when the treatment is limited to only one heating session. A solution to this problem is given by using simultaneously the rectal and urethral applicators. A complete 915-MHz microwave thermotherapy system is presented with two applicators which can operate independently or simultaneously to deliver the microwave energy in the prostate. Electromagnetic and thermal modeling have been developed for the applicator antenna optimization, to calculate the specific absorption rate (SAR) and the thermal pattern in the prostate for each applicator alone and when they operate together in phase. Different canine experiments have been performed to prove the interest of using the two applicators simultaneously as compared when they operate alone. Histological examination cuts of the prostate gland after heating have been carried out.

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. >

Combination of Local Heating and Radiometry by Microwaves

New methods for combination of microwave heating and microwave radiometry are presented. The processes experimented with here make it possible to collect the thermal signal emitted in the very volume in which the power dissipation is achieved. They can be used for medical (atraumatic control of local hyperthermia) or industrial applications (regulation of microwave heating).

Methods of hyperthermia control

1 Thermometry in Therapeutic Hyperthermia.- 1.1 Introduction.- 1.2 Clinical Considerations.- 1.2.1 Practical Applications.- 1.2.2 Temperature Control.- 1.3 Available Technologies.- 1.3.1 Thermocouple Thermometry.- 1.3.2 Electrical Resistance Thermometry.- 1.3.3 Gallium Arsenide Optical Thermometry.- 1.3.4 Photoluminescent Thermometry.- 1.4 Measurement Errors and Artifacts.- 1.4.1 Calibration and Drift.- 1.4.2 Thermal Smearing.- 1.4.3 Electromagnetic Artifacts.- 1.4.4 Ultrasound Artifacts.- 1.5 Future Developments.- 1.5.1 Noninvasive Thermometers.- 1.5.2 Mathematical Modeling.- 1.6 Summary.- References.- 2 Noninvasive Control of Hyperthermia.- 2.1 Introduction.- 2.2 General Considerations Regarding Imaging Technique Performances.- 2.2.1 Presentation.- 2.2.2 Expected Performances for Noninvasive Control of Hyperthermia.- 2.2.3 Classification of Imaging Modalities.- 2.2.4 Analysis of Image Content.- 2.2.5 Usual Criteria of Image Quality.- 2.2.6 Temperature Dependence of Images.- 2.2.7 Other Practical Considerations.- 2.2.8 Optimization of Performances.- 2.3 Electromagnetic Radiometric Techniques.- 2.3.1 Presentation.- 2.3.2 Natural Limitations.- 2.3.3 Recent Developments.- 2.3.4 Discussion.- 2.4 X-Ray Tomodensitometry.- 2.4.1 Presentation.- 2.4.2 Fundamentals.- 2.4.3 Image Quality.- 2.4.4 Temperature Dependence of CT Numbers.- 2.4.5 Some Results.- 2.4.6 Discussion.- 2.5 NMR Tomography.- 2.5.1 Fundamentals.- 2.5.2 Image Quality.- 2.5.3 Temperature Dependence of NMR Imaging Parameters.- 2.5.4 Some Results.- 2.5.5 Discussion.- 2.6 Imaging of Dielectric Properties.- 2.6.1 Presentation.- 2.6.2 Fundamentals.- 2.6.3 Salient Features of Dielectric Properties of Living Tissues.- 2.6.4 Electrical Impedance Tomography.- 2.6.5 Microwave Imaging.- 2.6.6 Radiofrequency Inverse Scattering Techniques.- 2.6.7 Conclusion.- 2.7 Ultrasonic Techniques.- 2.7.1 Presentation.- 2.7.2 Sensitivity of Living Tissue Characteristics to Temperature.- 2.7.3 Active Modalities.- 2.7.4 Ultrasound Radiometry.- 2.7.5 Thermo-induced Acoustic Imaging.- 2.7.6 Discussion.- 2.8 Discussion, Synthesis, and Prospects.- References.- 3 Use of Microwave Radiometry for Hyperthermia Monitoring and as a Basis for Thermal Dosimetry.- 3.1 Introduction.- 3.2 Measurement of Thermal Radiation.- 3.2.1 Physical Principles: The Black Body Radiation.- 3.2.2 Thermal Power Collected by an Antenna: Nyquists Formula.- 3.2.3 Thickness of Medium and Radiometric Measurement.- 3.2.4 Reflection Effects at the Air-Medium Interface.- 3.2.5 Characteristics of the Radiometric Method for Temperature Measurement.- 3.3 Microwave Radiometric Systems.- 3.3.1 The Dicke Radiometer: Principle and Limitations.- 3.3.2 The Modified Radiometer.- 3.3.3 Description and Performances of the Radiometer Used for Medical Applications Performances of the Applicator Antenna.- 3.4 Control of Hyperthermia by Microwave Radiometry.- 3.4.1 Principles and Problems.- 3.4.2 Design of the Microwave Systems.- 3.4.3 Performances and Possibilities: Examples of Experiments on Phantoms, Animals, and Patients.- 3.4.4 Use of Microwave Radiometry to Control Radiofrequency Hyperthermia.- 3.5 Thermal Dosimetry for Microwave Hyperthermia Based on Microwave Radiometry.- 3.5.1 Principles of the Method.- 3.5.2 Computation of the Radiometric Signal.- 3.5.3 Computation of Thermal Profile Using the Bioheat Transfer Equation.- 3.5.4 The Inverse Process.- 3.5.5 Examples of Results Obtained with These Programs: Theory-Experiment Comparisons.- 3.6 Conclusion.- References.

Microwave thermochemotherapy in the treatment of the bladder carcinoma-electromagnetic and dielectric studies-clinical protocol

Microwave thermotherapy is currently used in clinical routines for benign prostatic hyperplasia treatments. The temperature increase is obtained using an endocavitary microwave applicator placed in the prostatic urethra. This urethral applicator after a technical modification can be placed inside the bladder in order to potentiate the effects of the treatment by chemotherapy of vesical carcinoma. This paper deals with electromagnetic studies of this new endocavitary applicator. First of all, the experimental determination of the dielectric permittivities for the propagation domain characterization is achieved in order to be used in the electromagnetic model. Compared to experimental results, these simulations obtained by the finite-difference time-domain formalism allow us to determine the electromagnetic performance of this applicator. Finally, the in vivo study realized on anesthetized dogs to determine the therapeutic protocol associating chemotherapy and thermotherapy in the treatment of the bladder cancer is presented.

Modeling of various kinds of applicators used for microwave hyperthermia based on the FDTD method

Interstitial and endocavitary applicators, which have been designed and developed for microwave hyperthermia treatments controlled by microwave radiometry, are modeled using the finite difference time domain (FDTD) method. For each type of applicator, the numerical results concerning the reflection coefficient S/sub 11/, the power deposition, and the heating patterns are given. These results are compared with measurements performed on phantom models of human tissues and show good agreement. Possibilities for future developments are discussed.

Coaxial antenna array for 915 MHz interstitial hyperthermia: design and modelization-power deposition and heating pattern-phased array

Coaxial antennas different in their active length have been designed for use in a complete 915-MHz hyperthermia system with temperature control by microwave radiometry. Heating patterns are reconstructed from the power deposition associated with the bioheat transfer equation. Temperature control is effected by means of microwave radiometry and used in order to determine bioheat parameters. Phased arrays are studied allowing heated volume expansion. >

Progress in Microwave and Radiofrequency Hyperthermia Controlled by Microwave Thermography

Previous feasibility experiments have indicated the possibility of achieving microwave local heating and microwave thermography with the same system.1,2 This combined process is now available for measurement and control of the local increase of temperature in hyperthermia therapy. Several systems have been built according to this principle3,4,5 which are intended for biomedical applications.

Microwave interstitial hyperthermia controlled by microwave radiometry: technical aspects, animal experiments and first clinical results

The microwave and thermal performance of a microwave interstitial hyperthermia system with temperature controlled by microwave radiometry is discussed. Miniature coaxial antennas have been designed for heating at 915 MHz or 434 MHz and for radiometric temperature measurements around 3 GHz and 9 GHz. The feasibility of this system has been demonstrated by experiments on an acrylamide phantom, and the first clinical results are promising.<<ETX>>