Local Current Field Research Articles

Estimation of temperature distribution inside tissues heated by interstitial RF electrode hyperthermia systems.

The computational method presented relies on a semi-infinite tissue model. The needle-shaped RF electrodes are modeled with elongated spheroids. The heat transfer problem is treated in three dimensions. The localized current fields set up inside the tissue from the discrete implants are computed by using electrostatic methods, and the bioheat diffusion equation under a steady-state condition is solved to determine the temperature distributions inside superficial tissues. A Green's-function technique is applied to solve the bioheat transfer equation. The heat removal due to blood circulation is also taken into account. Analytical techniques are used to treat the singularities in the vicinity of implanted electrodes. Numerical results are presented for several electrode configurations. >

Advanced technique in localized current field hyperthermia.

Interstitial localized current field (LCF) hyperthermia has gained a good reputation as an excellent method for heating localized tumors (Joseph et al. 1981; Manning et al. 1982; Cosset et al. 1984; Goffinet et al. 1985; Vora et al. 1986; Linares et al. 1986; Emami and Perez 1985). Heating is performed by means of ohmic currents flowing through tissue between implanted electrodes. To gain a homogeneous temperature distribution throughout the tumor volume even if perfusion is not uniform it is necessary to continuously measure temperature inside the tumor at many points of interest. Temperature differences can be reduced by altering the specific absorption rate (SAR).

Spiral superconducting NbTi filaments: electric field and critical current

As a first step to a better understanding of the voltage—current characteristics of fine filament multifilamentary composite superconductors, the electric field and critical current along a single spiral-shaped filament were studied. When the spiral superconducting filament was carrying constant current and placed in a magnetic field, the local critical current and electric field vary due to the change of the angle between the magnetic field and filament axis. A theory is presented which enables us to calculate the mean and local values of the electric field and critical current of spiral samples for arbitrary orientation between the magnetic field and spiral axis. The presented experimental results are in good agreement with this theory.

Interstitial thermoradiotherapy in treatment of malignant tumours.

From October 1981 to October 1985, 48 recurrent/persistent tumours (46 patients) were treated with a combination of interstitial hyperthermia and interstitial radiation therapy. All patients had failed other conventional treatment modalities. Radiation was administered using 192Ir with doses varying from 2000 to 6000 rad, depending on the dose of previous irradiation. Hyperthermia was administered with either localized current fields (LCF) or microwaves, two sessions each, minimum tumour temperature of 42.5 degrees C for 60 min. Of 37 lesions treated with at least one satisfactory hyperthermia session, there were 26 of 37 (70 per cent) complete responses and 11 of 37 (29.7 per cent) partial responses. Of 11 lesions with no sessions of satisfactory hyperthermia, there were no complete responses and only five partial responses. The detailed results are presented.

A 500 KHz localized current field hyperthermia system for use with ophthalmic plaque radiotherapy.

Ophthalmic plaque radiotherapy has been demonstrated to be a useful alternative to enucleation in the treatment of small choroidal melanomas. The prognosis for tumours larger than 8 mm in height, however, continues to be poor. Treatment complications limit the radiation dose which may be delivered to these larger tumours. Hyperthermia has been shown to enhance the effectiveness of radiotherapy for many tumours, particularly malignant melanoma. The use of hyperthermia in conjunction with plaque radiotherapy may improve local tumour control for larger choroidal melanomas, allowing patients to maintain useful vision. We have developed an instrument which enables the combination of localized current field hyperthermia with radiotherapy using an episcleral plaque. The system is simple and inexpensive. We have measured temperature distributions in tissue-like phantoms, in excised bovine eyes, and in vivo in normal rabbits. In each of the cases studied, temperature varied by less than 1 degree C within 3 mm of, and across the concave surface of the plaque. At distances greater than 3 mm, the temperature gradient was approximately -0.3 degree C per millimetre.

Analysis of prognostic variables in hyperthermia treatment of 161 patients

From 1977–1982, 161 patients were treated using hyperthermia as an adjuvant in Phase I trials. Microwave applicators (MW), capacitively coupled plates (RF plates), interstitial localized current fields (LCF), and magnetic induction heating (MI) techniques were used together with radiation in 135 patients, with chemotherapy in 10 patients, and alone in 16 patients. Tumor volume response categories were no response (NR, less than 50% decrease); partial response (PR, 50% ⪕ volume decrease < 100%); and complete response (CR, complete disappearance). The CR rates and total response rates (CR + PR) were 38/160 (24%) and 90/160 (56%), respectively. There were highly significant differences among techniques in CR vs PR + NR ( p = .001), and in CR + PR vs NR ( p < .0005). Response did not vary significantly with histologic category. Overall toxicity was 16%, and did not vary significantly with technique ( p = .193). In the patient group treated with hyperthermia and radiation, multivariate analysis revealed that a set of three variables had prognostic importance for CR: technique ( p = .011), radiation dose ( p = .019), and tumor volume ( p = .001, negatively correlated). A good correlation also existed between CR and the minimum tumor temperature averaged over all treatments, T MIN (P < .0005 ). Temperature variables themselves were correlated with tumor volume. Minimum T correlated negatively with volume ( p = .017) and T MAX correlated positively with volume ( p = .026). In fewer than 50% of patients could minimum T > 40.7° C be achieved. Our conclusions are: 1) T MIN , tumor volume, radiation dose, and heating technique have prognostic value for initial response; 2) variation in CR vs technique reflects variation in tumor volume treated and in minimum temperature achieved with these techniques; and 3) acute toxicity of treatment is infrequent, but serious toxicity is possible with the interstitial technique.

Local current field radiofrequency hyperthermia for the treatment of superficial skin tumours in cats

Local current field radiofrequency (LCF-RF) hyperthermia was used to treat 38 superficial skin tumours (predominantly squamous cell carcinomas) of the nose, face and ears in 35 cats. LCF-RF hyperthermia was applied at 50 degrees C for 60 seconds at single or multiple sites depending on the tumour size. Each cat was observed over a four-month period after treatment and 14 out of 35 cases were also available for re-evaluation eight months after treatment. Tumours which had not resolved completely within one month after the initial treatment were re-treated. LCF-RF hyperthermia is most suited for the treatment of superficial skin tumours (<5 mm diameter). Ninety-two per cent (12/13) of tumours of this dimension showed some regression and 69% (9/13) completely resolved. Larger tumours >5mm diameter) were also successfully treated. 54% (8/14) regressed but only 14% (2/14) completely resolved. LCF-RF hyperthermia is not recommended for the treatment of tumours of the pinnae as 5 of the 6 tumours at this site failed to respond.

Interstitial implant with interstitial hyperthermia.

A Phase I Pilot Study combining interstitial or intracavitary irradiation using 192Ir or 137Cs and interstitial hyperthermia in advanced or recurrent tumors is underway at the City of Hope National Medical Center. Hyperthermia is performed using 0.5 megahertz RF (500 kilohertz) radiofrequency localized current fields. In the implanted volume, a temperature of 41 degrees to 45 degrees C is maintained for 30 to 40 minutes. Hyperthermia is performed prior to irradiation in all patients. All patients had either failed previous conventional treatments, including surgery, chemotherapy and/or radiation therapy, or had advanced malignant tumors which were not felt to be controllable by conventional means. Sixteen lesions were implanted in 15 patients. Of the 16 lesions, 11/16 (68%) achieved complete response, and three had no response or recurred locally. The six patients (100%) receiving interstitial implant and hyperthermia as the primary therapy achieved complete response. Normal tissue complications were minimal. Range of response was three to 13 months. Interstitial thermoradiotherapy appears to be a safe and promising mode of therapy in advanced or recurrent accessible malignant tumors.

A localized current field hyperthermia system for use with 192-iridium interstitial implants.

The efficacy of localized current field (LCF) hyperthermia as an adjunct to 192Ir interstitial implantation of tumors is currently under investigation. In this article, we describe an experimental LCF system suitable for such investigations, and discuss some of the physical and biological parameters pertinent to its design and safe operation.

Microscopic and Macroscopic Aspects of Nuclear Dynamics in Mean-Field Approximation. (I. Formalism)

A macroscopic approach to the quantum self-consistent Boltzmann equation is suggested. With the crucial introduction of a quasi-equilibrium assumption about the underlying nuclear distribution function, the usual time-dependent Hartree-Fock equation can be reduced to those of hydrodynamics for local density, current and internal energy density fields. Solutions to these macroscopic equations produce the smooth quasi-equilibrium distribution function and allow one to extract the irregular contribution to the exact quantal Wigner function. The effects of viscosity which arise from two-body collisions are examined in this context. Formulated in a slab geometry, this problem has been solved by a straightforward comparison between the exact quantal and the quasi-equilibrium distribution.

Localized current field heating as an adjunct to radiation therapy

The purpose of this paper is to report the results of a pilot study using hyperthermia as an adjunct to radiation therapy in the treatment of malignant disease, spontaneously occurring in domestic animals. Localized current fields (LCF) have been used to produce the hyperthermia. The aim of the pilot study was to establish a reasonable dose regime for testing in a randomized trial. The doses tested ranged from an equivalent 3,000 rads in 3 weeks to 6,000 rads in 6 weeks for the radiation treatments and 43 degrees C for 30 min to 45 degrees C for 30 min for the hyperthermia treatments. To date, there have been either complete or partial (over 50% tumor regression) responses in 82.9% of the animals and complete regression in 54.3% of the tumors. The details of the randomized trial are described.

A temperature regulating circuit for experimental localized current field hyperthermia systems.

Interest in localized current field (LCF) hyperthermia tumor therapy is rapidly increasing. As yet, however, there is no integral LCF system commercially available. An experimental LCF system may be readily assembled from discrete, general purpose components, except for the tumor temperature regulating circuitry. In this article we present an LCF system designed around general purpose components and a simple circuit for temperature regulation. Comments on system safety, calibration, and performance are also included.

Ring current effects in the conformation dependent NMR chemical shifts of aliphatic protons in the basic pancreatic trypsin inhibitor

Previously, a highly refined crystal structure and energy refined atomic coordinates were obtained for the basic pancreatic trypsin inhibitor, as well as numerous individual resonance assignments in the 1H NMR spectrum. These data were now used to investigate the contributions from the local ring current fields of the aromatic rings to the overall conformation dependent chemical shifts in this globular protein. A program was written which allowed the consideration of certain aspects of internal mobility of the protein, and the different commonly used ring current equations were compared. These studies indicate that ring current shifts are the dominant contribution to the observed conformation dependent chemical shifts of the peripheral aliphatic side chain protons. On the other hand, it appears that ring current shifts do not make dominant contributions to the conformation dependent shifts of the backbone α- and amide protons or the aromatic protons in the inhibitor. On the basis of the empirical calibration with the peripheral aliphatic side chain protons, the Johnson-Bovey ring current equation was selected for an analysis of the ring geometries of two prolines in the inhibitor.

The potential of localized heating as a adjunct to radiation therapy.

Experimental studies have shown that (a) tumor cells may be more sensitive to heat than normal cells; (b) hyperthermia inactivates cellular repair mechanisms for radiation damage; and (c) heat may lower the OER for ionizing radiation (anoxic cells are at least as sensitive to hyperthermia as oxygenated cells). Localized hyperthemia produced by localized current fields in the range of 100 kHz-10 MHz by direct contact electrodes offers two major advantages: the eletrode configurations may be manipulated to obtain desired thermal dose distributions, and, since the mode of heating is essentially instantaneous, accurate temperature control can be maintained during treatment.