A 27-MHZ CURRENT SOURCE INTERSTITIAL HYPERTHERMIA SYSTEM FOR SMALL ANIMALS

Temperature distribution is an important factor in thermo-radiotherapy and it is greatly dependent on the applied heating technique. Consist ency of the heating method is therefore important in translating in vi vo experimental data to the clinical situation. To further evaluate th e combination of interstitial hyperthermia and interstitial radiothera py, an experimental interstitial hyperthermia system has been develope d for small (500-2000 mm(3)) tumours growing in the flank of a rat. Th e system used reproduces the properties of our clinical current source interstitial hyperthermia system. The heating system consists of four applicators, each with independent tuning and power control. The appl icators are situated inside plastic afterloading catheters and are cap acitively coupled with the surrounding tissue. The tumour is heated th rough dissipation of a 27 MHz current flowing to an external ground pl ane. An effective RF-filter allows reliable thermocouple temperature m easurements when the power is switched on. The tumour temperature is e asily controlled by means of a continuous temperature read-out and a c lear temperature display. A minimum temperature up to 46 degrees C can be reached within 4-10 min and maintained (+/- 0.5 degrees C) through out the treatment period. Modelling calculations performed for this he ating system indicate that the applicator temperatures should be kept equal in order to minimize the difference between maximum and minimum tumour temperature. Significantly higher applicator currents are neede d at larger distances from the ground plane. In addition, the homogene ity of the temperature distribution is improved when either the tumour is isolated or when the environmental temperature is increased. The c alculations also show that temperature distribution is strongly depend ent on effective heat conductivity. A description of the system and it s performance is presented.