[Effects of needle heating: studies in normal canine liver]

Hyperthermia has great potential as an anti-hepatic tumor agent because it has not only direct anti-tumor effect by itself but also synergistic effect in combination with radiotherapy or chemotherapy. Focal hyperthermia can be produced by needle-type heater implanted directly into the tumor. Hyperthermic effect of this needle heating and the influence of tissue blood flow on it were studied in normal canine liver. Fifty V heating for 10 minutes (5208 joule) by needle-type heater produced the effective thermal field, 27mm in diameter, above 42 degrees C. Tissue temperature dropped rapidly with the increase of distance from the heater, which reveals that hepatic tumor can be heated selectively by this method. The relation between the tissue blood flow and hyperthermic effect was investigated in the conditions that hepatic perfusion was controlled by clamping either hepatic artery or portal vein, or both of them. The effective thermal volume, 24.4cc, in normal liver tissue with no perfusion was compared with 10.3cc in normal liver tissue with normal perfusion (88.1ml/min/100g), which means that heat delivered in tissue by needle heater is rapidly dissipated by the flowing blood. The microscopical findings one week after heating revealed that normal liver tissue was irreversibly damaged by heating above 46 degrees C for more than 5 minutes.