Fundamental Aspects of Electromagnetic Hyperthermia in Medicine.

This article considers the fundamental advantages of electromagnetic hyperthermia over different techniques for heating the human being's body. It also presents basic parameters that characterize hyperthermia and electromagnetic techniques for heating biological tissues. Apart from that, engineering solutions directed at providing effective hyperthermia are outlined.

[The efficacy of simultaneous and sequential irradiation and hyperthermic treatment of tumor cells in vitro and transplantable tumors in vivo].

The elevated efficacy of simultaneous treatment of cancer by irradiation and hyperthermia in comparison with their sequential application was confirmed in the experiments with V-79 cells in vitro and transplantable melanoma B-16 and ELD solid carcinoma in vivo. Irradiation of the tumors transplanted in the calf muscle of mice was performed at the extended Bragg peak of accelerated protons, while extremities of the group of 6 animals were fixed one after another in a water bath at 42 degrees C (hyperthermia) or at 36 degrees C (irradiation at normal temperature). In another series of experiments, the tumors were heated with the microwave (2450 MHz) antennae and irradiated on the 60Co clinical machine. The tumor temperature (42-43 degrees C) was permanently measured with a sensor based on p-i-n diode. In all cases, a hyperthermic treatment lasted 1 h and started either 15 min before irradiation (simultaneous use of both modalities) or 1 h after the end of irradiation, as is usually performed at many institutions. These results, demonstrating a notably better effect of a simultaneous treatment using the cell clonogenicity, the dynamic of tumor regression and the survival of animals as endpoints, made it possible to initiate the development and production of microwave antennae suitable for use during tumor irradiation in clinic.

Computational evaluation of changes in ionizing radiation dose distribution in tissues caused by EM applicators when external radiation and hyperthermia act simultaneously.

PURPOSE: The presented theoretical study investigates the influence of CFMA-like electromagnetic microstrip applicators (MAs) on ionizing radiation intensity and depth radiation dose distribution (DRDD) in irradiated tissues which are tightly covered with a MA. METHODS: It is shown that at relatively low photon energy (<200 keV) the MA does not affect noticeable the profile of the DRDD curve and does not lead to skin overdosing. Nevertheless, it significantly (up to 20-35%) decreases the low energy ionizing radiation intensity. For high energy photons (>1 MeV), on the contrary, the decrease of radiation intensity, caused by the MA, is small (3-10%), but the profile of the DRDD curve, calculated by means of the Monte-Carlo method, is significantly affected. RESULTS: The radiation dose maximum is shifted to the skin, resulting in possible skin overdosing. Radiation absorption characteristics of MA are calculated and compared with published parameters of EM horn and US applicators now in use for external simultaneous radiation and hyperthermia (ESRH) procedures. The MA provides the minor ionizing radiation absorption. Due to it and owing to their conformability with the tissue surface the MAs would not require any additional means or devices to be used for ESRH treatment procedures with any common ionizing radiation equipment. CONCLUSIONS: The necessity of development means for decreasing the time of radiation equipment occupation during ESRH procedures is pointed out.

Assessment of the performance characteristics of a prototype 12-element capacitive contact flexible microstrip applicator (CFMA-12) for superficial hyperthermia.

The electrical performance of the CFMA-12 operating at 433 MHz is assessed under laboratory conditions using a RF network analyser. From measurements of the scattering parameters of the CFMA-12 on both a multi-layered muscle- and fat/muscle-equivalent phantom, the optimal water bolus thickness, at which the transfer of the energy to the phantom configuration is maximal, is determined to be approximately 1 cm. The SAR distribution of the CFMA-12 in a multi-layered muscle-equivalent phantom is characterized using Schottky diode sheets and a TVS-600 IR camera. From the SAR measurements using the Schottky diode sheets it is shown that the contribution of the E(x) component to the SAR (SAR(x)) is maximal 7% of the contribution of the E(y)component to the SAR (SAR(y)) at different layers in both phantom configurations. The complete SAR distribution (SAR(tot)) at different depths is measured using the power pulse technique. From these measurements, it can be seen that SAR(y)at a depth of 0 cm in the muscle-equivalent phantom represents up to 80% of SAR(tot). At 1 and 2 cm depth, SAR(y) is up to 95% of SAR(tot). Therefore, in homogeneous muscle-equivalent phantoms, E(y) is the largest E-field component and measurement of SAR(y) distribution is sufficient to characterize SAR-steering performance of the CFMA-12. SAR steering measurements at 1 cm depth in the muscle-equivalent phantom show that the SAR maximum varies by 40% (1 SD) around the average value of 38.8 W kg(-1) (range 10-65 W kg(-1)) between single antenna elements. The effective fieldsize (E(50)) varies by 14% (1 SD) around the average value of 19.1 cm(2).

Morphological changes in the liver after microwave destruction.

We studied morphological changes in the liver after local MW-destruction. Microwave radiation damaged vascular walls with the formation of extensive necrotic focus; demarcation zone appeared 24 h after exposure, encapsulation occurred after 7 days, and replacement with a fine cicatrix formed by mature connective tissue after 4 months.

Technical aspects of electromagnetic hyperthermia in medicine.

This article considers the fundamental advantages of electromagnetic hyperthermia over different techniques for heating the human being's body. It also presents basic parameters that characterize hyperthermia and electromagnetic techniques for heating biological tissues. Apart from that, engineering solutions directed at providing effective hyperthermia are outlined.

Resonance effects in applicator water boluses and their influence on SAR distribution patterns.

Spurious electromagnetic oscillations in the water layer of applicator water boluses are investigated. Two oscillation types--volume oscillations (VO) and surface standing wave oscillations (SWO)--are considered. Conditions leading to their excitation in water boluses, commonly used in clinical practice for local hyperthermia, are examined. It was found that the thickness d of the water layer is the main critical parameter which determines the possibility of spurious oscillation modes excitation. Analytical equations are derived, allowing calculations of critical d(c) and resonance d(r) values for a given water bolus, and determine the approximate structure of electrical field strength distribution at its radiating plane, taking account of spurious oscillations. Calculated d(c) and d(r) values are in satisfactory quantitative agreement with experimental data, whereas experimentally observed complicated SAR distribution perturbations correlate qualitatively with the calculations in terms of volume and/or surface standing wave oscillations excited within the water bolus.

A HF EM installation allowing simultaneous whole body and deep local EM hyperthermia.

The structure and main features of a HF EM installation based upon a new approach for creating electromagnetic fields destined for whole body (WBH) and deep local (DLH) hyperthermia are discussed. The HF EM field, at a frequency of 13.56 MHz, is created by a coplanar capacity type applicator positioned under a distilled water filled bolus that the patient is lying on. The EM energy being released directly in the deep tissues ensures effective whole body heating to required therapeutic temperatures of up to 43.5 degrees C, whereas the skin temperature can be maintained as low as 39-40.5 degrees C. For DLH, the installation is equipped with additional applicators and a generator operating at a frequency of 40.68 MHz. High efficiency of the WBH applicator makes it possible to carry out the WBH procedure without any air-conditioning cabin. Due to this, a free access to the patient's body during the WBH treatment is provided and a simultaneous WBH/DLH or WBH/LH procedure by means of additional applicators is possible. Controllable power output in the range of 100-800 W at a frequency of 13.56 MHz and 50-350 W at a frequency of 40.68 MHz allows accurate temperature control during WBH, DLH and WBH/DLH procedures. SAR patterns created by the WBH and DLH applicators in a liquid muscle phantom and measured by means of a non-perturbing E-dipole are investigated. The scattered EM field strength measured in the vicinity of the operating installation during the WBH, DLH and WBH/DLH procedures does not exceed security standards. Examples of temperature versus time graphs in the course of WBH, DLH and WBH/DLH procedures in clinics are presented. The installation is successfully used in leading oncological institutions of Russia and Belarus, though combined WBH/DLH procedures are evidently more complicated and demand thorough planning and temperature measurements to avoid overheating.

An attempt at quantitative specification of SAR distribution homogeneity.

A homogeneity coefficient (HC) is suggested allowing quantitative evaluation of SAR distribution homogeneity over the heated area. Its efficacy in appreciation of SAR patterns quality is demonstrated on idealized and real SAR distributions. The HC parameter of a series of applicators widely used in clinics are calculated. HC could be assumed as a useful parameter additional to the qualified effective field size (EFS) in characterizing the applicator's properties.

[Use of ultra high-frequency electromagnetic fields in pediatric surgery]. / Primenenie sverkhvysokochastotnogo élektromagnitnogo polia v detskoi khirurgii.

The procedures associated with the application of a super-frequency electromagnetic field (SFEMF) are being introduced into a therapeutical process in their various modifications at the Pediatric Surgery Hospital of Russian State Medical University. This has been preceded by enormous experimental work aimed at evaluating the potentialities of SFEMF for potentiation of cryogenic exposure and for individual use for endovascular occlusion and local hyperthermia. A total of 947 patients were treated with SFEMF from 1979 to 1990. The largest group included children with hemangiomas of various site (n = 465) and those with cheloid scars (n = 395). Thirty-one patients underwent intravascular coagulation with SFEMF in the treatment of arterial and venous malformations and 31 patients were treated for pigmentary spots of various site with SFEMF + cryodestruction. Local hypothermia was performed in 25 children with extensive hemangiomas of the face and neck with SFEMF. The total therapeutical benefits reached 98%. For these purposes the authors used a Plot routine apparatus, 915 mHz, with a set of contact and special emitters. The experience with SFEMF in pediatric surgery suggests that it is highly effective and the trend is promising.

[Local microwave hyperthermia in the combined treatment of malignant tumors of the eyelids and orbit]. / Lokal'naia sverkhvysokochastotnaia gipertermiia v kompleksnom lechenii zlokachestvennykh opukholei vek i orbity.

The paper is concerned with the results of experimental investigation of the effect of different microwave radiation ranges on some segments of the rabbit's eye and its clinical application to the treatment of malignant tumors of the lid and orbit. It has been shown that the effect of definite microwave radiation ranges on the rabbit's eye, while ensuring necessary conditions for local hyperthermia (43-45 degrees C), does not cause clinically visible changes in the refractive media and fundus of the eye during 3 months after irradiation. The results of effective combined therapy of advanced malignant tumors of the lid and orbit in 5 patients are presented. Our experience in using definite ranges of local microwave radiation for therapy of malignant eye tumors has shown the feasibility, prospects and relative safety of the method in cancer ophthalmology.

[Effect of an ultrahigh-frequency electromagnetic field on the heat conductivity of experimental biological tissue]. / Vliianie sverkhvysokochastotnogo élektromagnitnogo polia na teploprovodnost' biotkani v éksperimente.

It has been established that heat conductivity was markedly increased after UHF-irradiation. The combined use of UHF-irradiation and cryogenic destruction is 30-40 times as effective as cryogenic destruction alone.

[Radiators for electromagnetic hyperthermia of malignant intracavitary neoplasms]. / Izluchateli dlia élektromagnitnoi gipertermii vnutripolostnykh zlokachestvennykh novoobrazovanii.

Rod radiators of electromagnetic field designed for electromagnetic hyperthermia of tumors of the body cavities were developed. Their main parameters were investigated in laboratories. Experimental samples of radiators were advanced for clinical trial in the leading cancer institutes of the country.