Tumor ablation at low frequencies for preferential tumor heating: initial ex-vivo tissue studies

Radiofrequency (RF) ablation is a common treatment modality for inoperable liver cancer. Several studies have demonstrated that significant differences exist between the electrical properties of tumor and normal tissue, especially at lower frequencies. In this study, we investigated in an ex vivo setting whether the use of lower frequencies during ablation results in preferential heating of tumor tissue.

We created a setup consisting of adjacent layers (3 cm thick each) of tumor phantom (agar gel) and freshly excised normal porcine liver tissue in a saline bath. A standard RF needle electrode was placed such that half of the active electrode was in each layer. We applied 25 W of power at a frequency of either 20 or 325 kHz to the electrode for 12 minutes. Temperatures were recorded 6 and 10 mm from the electrode in both the phantom and normal tissue layers.

The ratio of the temperature rise in the tumor phantom to the temperature rise in the normal tissue was significantly higher in the 20 kHz trials after 12 minutes at both 6 mm (1.50+/-0.27 vs. 1.02+/-0.16) and 10 mm (1.34+/-0.28 vs. 0.90+/-0.11) from the electrode (p<0.01).

Tumor ablation at frequencies lower than currently used may preferentially heat tumor tissue, preserving normal tissue at the treatment site.