RF-ablation pattern shaping employing switching channels of dual bipolar needle electrodes: ex vivo results

Bipolar radiofrequency ablation treatment of liver cancer employing monopolar needles: A comprehensive investigation on the efficacy of time-based switching

Radiofrequency ablation (RFA) is a thermal ablative treatment method that is commonly used to treat liver cancer. However, the thermal coagulation zone generated using the conventional RFA system can only successfully treat tumours up to 3 cm in diameter. Switching bipolar RFA has been proposed as a way to increase the thermal coagulation zone. Presently, the understanding of the underlying thermal processes that takes place during switching bipolar RFA remains limited. Hence, the objective of this study is to provide a comprehensive understanding on the thermal ablative effects of time-based switching bipolar RFA on liver tissue. Five switch intervals, namely 50, 100, 150, 200 and 300 s were investigated using a two-compartment 3D finite element model. The study was performed using two pairs of RF electrodes in a four-probe configuration, where the electrodes were alternated based on their respective switch interval. The physics employed in the present study were verified against experimental data from the literature. Results obtained show that using a shorter switch interval can improve the homogeneity of temperature distribution within the tissue and increase the rate of temperature rise by delaying the occurrence of roll-off. The coagulation volume obtained was the largest using switch interval of 50 s, followed by 100, 150, 200 and 300 s. The present study demonstrated that the transient thermal response of switching bipolar RFA can be improved by using shorter switch intervals.

Thermal and thermal damage responses during switching bipolar radiofrequency ablation employing bipolar needles: A computational study on the effects of different electrode configuration, input voltage and ablation duration

Recent studies have demonstrated the effectiveness of switching bipolar radiofrequency ablation (bRFA) in treating liver cancer. Nevertheless, the clinical use of the treatment remains less common than conventional monopolar RFA - likely due to the lack of understanding of how the tissues respond thermally to the switching effect. The problem is exacerbated by the numerous possible switching combinations when bRFA is performed using bipolar needles, thus making theoretical deduction and experimental studies difficult. This article addresses this issue via computational modelling by examining if significant variation in the treatment outcome exists amongst six different electrode configurations defined by the X-, C-, U-, N-, Z- and O-models. Results indicated that the tissue thermal and thermal damage responses varied depending on the electrode configuration and the operating conditions (input voltage and ablation duration). For a spherical tumour, 30 mm in diameter, complete ablation could not be attained in all configurations with 70 V input voltage and 5 minutes ablation duration. Increasing the input voltage to 90 V enlarged the coagulation zone in the X-model only. With the other configurations, extending the ablation duration to 10 minutes was found to be the better at enlarging the coagulation zone.

No-Touch Multi-bipolar Radiofrequency Ablation for the Treatment of Subcapsular Hepatocellular Carcinoma ≤ 5 cm Not Puncturable via the Non-tumorous Liver Parenchyma

PURPOSE

The percutaneous ablation of subcapsular hepatocellular carcinoma (S-HCC) may involve a risk of complications such as hemorrhage and tumor seeding, mainly linked to the direct tumor puncture often inevitable with mono-applicator ablation devices. The purpose of this study was to assess the efficacy and safety of no-touch multi-bipolar radiofrequency ablation (NTMBP-RFA) for the treatment of S-HCC ≤ 5 cm not puncturable via the non-tumorous liver parenchyma.

MATERIALS AND METHODS

Between September 2007 and December 2014, 58 consecutive patients (median age: 63 years [46-86], nine females) with 59 S-HCC ≤ 5 cm (median diameter: 25 mm [10-50 mm]), not puncturable via the non-tumorous liver parenchyma, were treated with NTMBP-RFA. Response and follow-up were assessed by CT or MRI. Complications were graded using the Cardiovascular and Interventional Radiological Society of Europe classification. Overall local tumor progression (OLTP)-free survival was assessed using the Kaplan-Meier method. A Cox proportional model evaluated the factors associated with OLTP. Signs of peritoneal or parietal tumor seeding were noted during follow-up imaging studies.

RESULTS

A complete ablation was achieved in 57/58 patients (98.3%) after one (n = 51) or two (n = 6) procedures. Three patients (5.2%) experienced complications (sepsis, cirrhosis decompensation; CIRSE grade 2 or 3). After a median follow-up period of 30.5 months [1-97], no patients had tumor seeding. The 1, 2 and 3-year OLTP-free survival rates were 98%, 94% and 91%, respectively. No factors were associated with OLTP.

CONCLUSION

NTMBP-RFA is a safe and effective treatment for S-HCC not puncturable via the non-tumorous liver parenchyma.

Roll-Off Displacement in Ex Vivo Experiments of RF Ablation With Refrigerated Saline Solution and Refrigerated Deionized Water

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.