Histopathogical changes of the normal liver by local hyperthermia were studied in rabbits. Hyperthermia was administered by an RF current heating divece with needle type applicators. Rabbits were allocated into 3 heated groups according to the treatment temperature and one control group. At laparotomy the left medial lobe of the liver was heated for 30 min at 38-39, 40-41 and 42-43 °C respectively. The livers were excised for the histopathological examination 1, 3, 7, 30, 90, and 180 days after the treatment. Irreversible changes did not occur after heating at lower than 41 °C. Extensive necrosis developed 1-7 days after heating at 42-43 °C and the necrotic area was gradually absorbed and replaced by fibrosis 30-180 days after heating.
These rusults indicate that the effect of local hyperthermia on the normal rabbit liver depends on temperatures and the irreversible change seems to occur when the liver is heated at higher than 42-43 °C.

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A two-dimensional numerical method for calculating electric field and specific absorption rate (SAR) distributions in a human body cross-section produced by a large waveguide applicator is developed using Fast-Fourier-Transform algorithm and conjugate gradient method. Severial examples of SAR distributions in a muscle-like cylinder model and a realistic model of a human body cross-section calculated by the method are given. Results of the numerical analysis show the possibility of deep tumor heating by the use of the large waveguide applicator. Large amount of energy is deposited in high-conductivity regions like kidney, muscle, and liver without excessive deposition in fat and bone.

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An attempt is made to control SAR distribution in a human body by the use of the large waveguide applicator in this paper. First, an example is worked out to show how the SAR distribution in a specfic region in liver can be increased by adjusting the position of the body in the waveguide applicator, relative to the SAR distribution in other regions of the body. This method is then applied to three cases of liver tumor based on CT-images. Results indicate that favorable SAR distributions can be obtained by positioning the region of tumor at around the center of waveguide applicator whose width is chosen at about 1. 5-2 times of the body width.

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Clinical applicator of hyperthermia is greatly hindered by the lack of appropriate apparatus for selective application of heat to the malignant tissues.
We investigated an endotract antennae for radio frequency (RF) for clinical application in rectal carcinoma. In the study we examined the physical and biological characteristics resulting from use of the applicator. In result this applicator has stable and sufficient capacity for heating purposes (4042°C) Tissue could be warmed quickly and safty, selecting adequit temperature in irrigation water.

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Eighty-four patients with unresectable various malignant tumors had received radiofrequency (RF) hyperthermia in combination with radiotherapy and /or chemotherapy. Hyperthermia was applied for 50 to 60 minutes once or twice weekly by using RF capacitive heat delivery systems operating at 8 or 13. 56 MHz. Of 84 tumors, 18 were superficial and 66 were deeply seated. These deeply seated tumors consisted of 21 primary tumors (TN group), 11 recurrent tumors (RC group), 24 primary or metastatic liver tumors (H group) and peritoneal disseminations (P group). The rate of CR (complete response) and PR (partial response) in total tumors was 31% whereas 7 tumors showed CR, 19 PR, 37 NC (no change), 11 PD (progressive disease) and 10 NE (not evaluable). Those regression rates in TN, RC, H, P groups and superficial group were 9.5, 18.2, 45.8, 0 and 61.1%, respectively. Subjective effects as pain relief, improvement of passage through the alimentary tract and so on emerged in 32. 1%. The regression rate was related not with histology of tumor but maximum intratumoral temperature. These results supported that RF hyperthermia with radiation and anticancer drugs was useful especially for liver and superficial tumors.

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