Sequential activation of multiple grounding pads reduces skin heating during radiofrequency tumor ablation.

PURPOSE: Radiofrequency (RF) tumor ablation has become an accepted treatment modality for tumors not amenable to surgery. Skin burns due to ground pad heating may become a limiting factor for further increase in ablation zone dimensions and generator power. We investigated a method were groups of ground pads are sequentially activated to reduce skin heating.
METHODS: We compared conventional operation (i.e. simultaneous connection of all pads) to sequentially switched activation of the pads where different pad combinations are active for periods of approximately 0.3 - 8 s. The timing during sequential activation was adjusted to keep the leading edge temperature equal between the pads. We created Finite Element Method computer models of three pads (5 x 5 cm, 1 cm apart) placed in line with the RF electrode on a human thigh to determine differences in tissue heating during simultaneous and sequential ground pad activation. We performed experiments with three ground pads (5 x 10 cm, 4 cm apart) placed on a tissue phantom (1.5 A, 12 min) and measured pad surface and leading edge temperatures.
RESULTS: Temperature rise below the leading edge for proximal, middle and distal ground pad in relation to active electrode location was 5.9 degrees C +/- 0.1 degrees C, 0.8 degrees C +/- 0.1 degrees C and 0.3 degrees C +/- 0.1 degrees C for conventional operation, and 3.3 degrees C +/- 0.1 degrees C, 3.4 degrees C +/- 0.2 degrees C and 3.4 degrees C +/- 0.2 degrees C for sequentially activated operation in the experiments (p < 0.001).
CONCLUSION: Sequential activation of multiple ground pads resulted in reduced maximum tissue temperature. This may reduce the incidence of ground pad burns and may allow higher power RF generators.