Hepatic radiofrequency ablation at low frequencies preferentially heats tumour tissue

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Abstract
Purpose: Radiofrequency ablation is a clinically accepted treatment modality for liver cancer. There are significant differences in dielectric properties between normal and cancer tissue in the liver, which are particularly pronounced at frequencies below 100 kHz. This study performed computer simulations to determine whether radiofrequency (RF) ablation at lower frequencies than currently employed (450–500 kHz) can take advantage of this difference to preferentially deposit energy within the tumour. Materials and methods: Finite Element Method computer models were created for a cooled needle electrode and a multi-tine RF electrode inserted into a 2 cm diameter tumour. RF ablation was simulated and current density as well as tissue temperature distribution determined. In vivo data were used on electrical conductivity of normal and cancer tissue in the models to simulate RF ablation in liver at the currently used frequency of 500 kHz and at 10 kHz. Results: At 500 kHz there was little difference in RF current density and final tissue temperature between normal and cancer tissue. Due to the more pronounced differences in electrical conductivity at 10 kHz, cancer tissue was heated preferentially at this frequency. Depending on power control algorithm, this resulted in either higher intra-tumour temperatures or lower temperatures outside the tumour at 10 kHz compared to 500 kHz. Conclusion: Radiofrequency ablation at lower frequencies than currently used may preferentially heat the tumour and preserve normal tissue. A targeted device for selective tumour destruction may be designed to make use of this principle.