Radiofrequency Ablation: Effect of Surrounding Tissue Composition on Coagulation Necrosis in a Canine Tumor Model

PURPOSE: To determine the effect of surrounding tissue type on coagulation necrosis from radiofrequency (RF) ablation in a homogeneous animal tumor model. MATERIALS AND METHODS: Thirty canine venereal sarcomas were implanted in three tissue sites (subcutaneous, kidney, and lung) in 13 mildly immunosuppressed dogs. Five of 25 tumors, which were 19 mm ± 3 (mean ± SD) in diameter, were allocated to each of five groups: (a) subcutaneous tumors, (b) kidney tumors, (c) lung tumors with blood flow, and (d) subcutaneous and (e) renal tumors without blood flow, which was achieved by sacrificing the animal to eliminate tumor perfusion. A sixth group comprised larger subcutaneous tumors (mean diameter, 46 mm ± 4) that were also treated. RF ablation was performed with a 1-cm tip and 5 minutes of ablation at 90°C ± 1. Impedance, temperature, and resultant coagulation diameter were recorded and compared. Data were analyzed statistically, including one-way analysis of variance to determine the effect of tissue conductivity (ie, systemic impedance) on necrosis size and tissue temperatures. Linear regression analysis was used to compare changes in impedance between the control and experimental groups. RESULTS: Increasing linear correlation was observed between tumor coagulation diameter and overall baseline system impedance (R² = 0.65). RF ablation of lung tumors resulted in the greatest coagulation diameter (13.0 mm ± 3.5) compared with that in the other groups (P < .01). The smallest coagulation diameter was observed in kidney tumors in the presence of blood flow (7.3 mm ± 0.6) compared with that in the other groups (P < .01). Elimination of blood flow in kidney tumors increased coagulation diameter to 10.3 mm ± 0.6 (P < .01). After RF ablation, coagulation diameter in the subcutaneous tumor groups was the same (mean, 9.8 mm ± 1.0) (difference not significant), regardless of tumor size of presence of blood flow. CONCLUSION: The characteristics of tissue that surrounds tumor, including vascularity and electric conductivity, affect ablation outcome. Predominance of tissue-specific characteristics will likely result in site-specific differences in RF-induced coagulation necrosis.