Prevention of Ground Pad During Radiofrequency Tumor Ablation

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DESCRIPTION (provided by applicant): Radiofrequency (RF) ablation is a promising, minimally invasive heat-based method used to ablate cancer of the liver, kidney, bone, and lung. Under imaging guidance, an electrode is inserted into the tumor, and radiofrequency current is applied to the electrode resulting in ionic agitation and tissue heating. The tumor is destroyed by coagulative necrosis once it reaches >50 ¿C. One of the major advantages of RF ablation is that it can be applied in a minimally invasive fashion, resulting in rapid patient recovery and low morbidity. Initial RF devices used 25 W power and created 1.5 cm diameter coagulation zones, while current devices use 200 - 250 W power and create 4-6 cm diameter coagulation zones. One major limitation of current RF devices is the inability to treat even moderate size tumors (> 3 cm) with a single ablation due to insufficient size of the coagulation zone. Therefore future devices will likely continue the trend towards higher generator power and multiple electrodes to increase the size of coagulation zone and decrease treatment times. A major obstacle in employing higher power RF generators and enabling increased coagulation zones is ground pad heating, which can lead to 3rd degree skin burns in severe cases. The current incidence of ground pad skin burns ranges from 0.1 - 3.2 % for severe skin burns (2nd or 3rd degree), with mild skin burns ranging between 5-33 %. Due to inhomogeneous distribution of RF current below the ground pads, the edge closest to the electrode is where the highest skin temperatures and burns are most likely occur. In clinical ablation procedures, two-to-four ground pads are placed equidistant from the ablation electrode, usually around the thighs. Adding additional ground pads further away from the electrode will only provide minimal improvement, since RF current travels preferentially to the closest pads. Attempts in reducing ground pad related heating so far have been limited to optimizing pad placement, pad shape, and cooling of the pads. We propose to modulate the RF current and associated heating below each pad by sequentially activating ground pads, and adding a layer of electrically conductive gel below the pads. Thereby RF current is distributed evenly among multiple pads, related heating is reduced, and pads can be placed arbitrarily without the current limitation of being at the same distance from the RF electrode. This method will enable higher generator power, and reduce the likelihood of skin burns. Relevance of this project to public health: Successful completion of this project will enable more effective treatment of liver cancer. Physicians will be able to treat larger tumors, treatment times will be reduced, and success rates may increase.