Sequential Activation of Ground Pads Reduces Skin Heating During Radiofrequency Tumor Ablation: In Vivo Porcine Results

Skin burns below ground pads during monopolar RF ablation are increasingly prevalent, thereby hindering the development of higher power RF generators capable of creating larger tumor ablation zones in combination with multiple or new applicators. Our goal was to evaluate reduction in skin temperatures via additional ground pads in an in vivo porcine model. Three ground pads placed on the animal's abdomen were activated either simultaneously or sequentially, where activation timing was adjusted to equilibrate skin temperature below each pad. Thirteen RF ablations (n = 4 simultaneous at 300 W, n = 5 sequential at 300 W, and n = 4 sequential at 375 W) were performed for 12 min via two internally cooled cluster electrodes placed in the gluteus maximus of domestic swine. Temperature rise at each pad and burn degree as determined via histology were compared. Ablation zone size was determined via T2-weighted MRI. Maximum temperature rise was significantly higher with simultaneous activation than with either of the sequential activation group (21.4°C versus 8.1°C or 9.6°C, p < 0.01). Ablation zone diameters during simultaneous (300 W) and sequential activations (300 and 375 W) were and 6.9 ± 0.3, 5.6 ± 0.3, and 7.5 ± 0.6 cm, respectively. Sequential activation of multiple ground pads results in significantly lower skin temperatures and less severe burns, as measured by histological examination.

I Introduction

RF ablation has been successfully utilized as a minimally invasive treatment for primary and metastatic liver tumors, as well as tumors in kidney, lung, bone, and adrenal gland tissue [1]–[6]. Since the introduction of RF ablation for tumor treatment, the inability to create large ablation zone volumes without multiple power applications has been a major limitation. While current commercial systems have allowed the creation of larger coagulation zones (4–6 cm) than initial systems (1.5 cm), partially due to an increase in maximum generator power (250 versus 50 W), recent studies have shown the possibility of obtaining even larger coagulation zones by using higher power levels (up to 1000 W) [7], [8]. However, it should be noted that not all applicators, currently in clinical use, will benefit from higher power, and new applicators may be required to take advantage of higher power levels.