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

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.

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.

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).

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.