Comparison of radiofrequency ablation processes for monopolar and bipolar systems

Most of the manufactured radiofrequency ablation devices use single electrodes inserted into the tumor for heating. In order to increase the volume of heating, they are cooled from the inside, and some have a system for wetting the outer surface of the electrode with saline. The need for necrosis of tumors with a diameter of more than 3 cm made us look for other design solutions that would significantly increase the volume of heated tissue. At the beginning, these were attempts to increase the number of heat sources inside the tumor by opening additional wires in the tumor, then the transition began to increase the number of electrodes to three and increase the number of working zones on each electrode. As a result, heating volumes of 90 cm3 were achieved with a heating time of 45 min. A study of the scientific and technical literature on RFA showed that foreign firms producing ablation devices already understand the need to replace monopolar electrodes with bipolar multi-electrode devices. The reason for this is not only the better postoperative characteristics of the use of bipolar electrodes, but also the emergence, in addition to oncology, of new areas of ablation application, where more complex forms of thermal fields are used during therapy, for example, tubular zones of necrosis. A radical solution to the problem of increasing the volume of coagulation is the transition from monopolar single electrodes to bipolar multielectrode designs. In this case, the electric field is concentrated in the areas between the electrodes and the heating efficiency increases significantly throughout the tumor volume, including the peripheral part. The most effective way is to incorporate bipolar electrodes into a circular cluster, allowing all electrodes to work simultaneously. Under the control of an ultrasound scanner, 4 to 12 electrodes are inserted, operating in bipolar mode. A model has been developed and the design of a four-electrode cluster has been developed, which allows for distributed heating of the tumor in a bipolar mode. As a result of the studies carried out, it was found that the use of bipolar systems allows: to significantly increase the volume of the area of necrosis due to the possibility of increasing the power supplied to the tumor; to reduce the unevenness of heating over the volume of the tumor by obtaining temperature fields, the shape of which is closest to the required one; improve patient survival rates by placing electrodes outside the tumor (“NO TOUCH” mode). The work performed indicates the technical possibility of a significant increase in the volume of destroyed tissue by increasing the number of electrodes and placing electrodes along the tumor volume closer to the periphery, including the ablastic zone. As a result, it became possible to heat tumors from their periphery without contacting the electrodes with the tumor. The increase in the number of heat sources made it possible not only to reduce the load on the electrodes, but also to shorten the procedure time. Ablation of large volumes entailed an inevitable increase in the number of electrodes in a multi-electrode system, which led to the complication of their connection to the generator. So far, an unresolved problem remains to reduce the total impedance of the generator load.