A cluster electrode system (E) for use with a high frequency generator (16) for inducing coherent high frequency heat ablation volumes within targeted tissue of a patient comprises a plurality of hollow electrodes (1, 2 and 3) wherein each electrode includes a rigid shaft having a sealed distal conductive tip (4, 5 and 6) for insertion into the target tissue of the patient and a proximal insulated shaft portion, wherein electrode (1, 2 and 3) is configured to allow circulation of a fluid therein. A reference electrode (19) is electrically connected to the generator (16) for placement in contact with the patient. The high frequency generator (16) is electrically connectable to each electrode (1, 2 and 3).
