The invention concerns a medical instrument for radio-frequency induced hyperthermia treatment of tumours. It is made up of a guide needle which houses two or more active radio-frequency wires connected at their proximal end to a radio-frequency generator and each one having a spiraled, helicoidal or spiral, distal segment. The wires can be moved longitudinally between a completely retracted passive position in the needle to an active position where the distal segments of the wires protrude from the distal end of the guide needle, automatically adopting a coiled shaped.
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