RESUMO
OBJECTIVE: The recurrence rate in the treatment of liver tumors using radio frequency ablation (RFA) is often related to incomplete tissue necrosis and consequently the limitation in the ablation volume. This paper proposes an ablation protocol combined with the infusion of saline solution and deionized water aiming at achieving a time displacement in the roll-off occurrence and consequently increasing the volume of ablation. METHODS: An infusion of saline solution and deionized water at 5 and 23 °C was performed to evaluate the influence of these liquids on the RFA procedure in ex vivo bovine liver pieces. The obtained results were used to propose a mathematical model of the roll-off phenomenon by means of the system identification techniques. RESULTS: The RFA combined with the infusion of saline solution 0.9% at 5 °C presented optimal results, with a time delay of the roll-off occurrence in 27.8% compared to pure RFA ( p = 0.002) and an increase in the necrotic volume of 51.2% ( p = 0.0002). Two Box-Jenkins models were obtained to describe the roll-off phenomenon: 1) pure RFA; and 2) RFA combined with the saline solution 0.9% at 5 °C. CONCLUSION: The RFA therapy combined with the saline solution 0.9% at 5 °C increases the time range to the roll-off occurrence, leading to higher necrosis volumes in ex vivo bovine liver samples. The development of a mathematical model to describe the roll-off behavior demonstrated that the transient response is improved by the infusion of the saline solution 0.9% at 5 °C.