Image-guided percutaneous chemical and radiofrequency tumor ablation in an animal model.

PURPOSE

To determine whether combining acetic acid instillation before radiofrequency (RF) ablation can improve local tissue electrical conductivity, RF energy deposition, intratumoral heating, and tumor necrosis in a large animal model.

MATERIALS AND METHODS

Multiple hypovascular canine venereal sarcomas were implanted in 11 mildly immunosuppressed dogs (25 mg/kg cyclosporin A twice daily). Tumors were incubated for 8-12 weeks to 4.2 cm +/- 0.6 in diameter. Treatment strategies included 10% and 15% acetic acid diluted in distilled water, 10% and 15% acetic acid diluted in saturated NaCl solution, 50% acetic acid, and 100% ethanol, with 6 mL of each injected alone or in combination with RF ablation (internally cooled, 1-cm tip; 12 minutes). Two additional control groups were studied in which tumors received either RF alone or distilled water injected alone. Comparisons were also made with groups treated with 36% NaCl with and without RF ablation. Resultant coagulation for these ablative strategies, along with local temperatures and RF parameters such as impedance, current, and power, were compared.

RESULTS

Increasing coagulation was observed with increasing acetic acid concentrations (1.7 cm +/- 0.4, 2.8 cm +/- 0.6, and 3.5 cm +/- 0.3 for 10%, 15%, and 50% acetic acid alone, respectively; P <.01). The combination of RF ablation with acetic acid resulted in greater coagulation than with either therapy alone (P <.05). However, maximum heating and coagulation were observed with 10% acetic acid diluted in NaCl, with which the entire tumor (diameter, 4.5 cm +/- 0.4) was completely ablated in every case. This was equivalent to results for tumors treated with 36% NaCl combined with RF. RF with a 50% acetic acid concentration resulted in coagulation measuring only 3.7 cm +/- 0.3 (P <.01). Significantly greater RF heating (89.7 degrees C +/- 12.3 at 10 mm) was observed when the tumors were pretreated with 10% or 15% acetic acid in saturated NaCl, compared with 67.9 degrees C +/- 13.7 observed when acetic acid was diluted in water (P <.02). RF combined with ethanol produced less coagulation (2.8 cm +/- 0.3) than combinations with acetic acid because rapid and irreversible impedance increases were observed.

CONCLUSION

Addition of acetic acid injections to RF ablation substantially increases tumor destruction compared with RF or injection therapy alone. However, lower acetic acid concentrations in saturated NaCl produced greater tumor coagulation, suggesting that, in this hypovascular tumor model, alterations in electrical conductivity play a more important role in increasing tumor ablation efficiency than do the additional ablative effects of acetic acid.