Heat Sink Effect on Tumor Ablation Characteristics as Observed in Monopolar Radiofrequency, Bipolar Radiofrequency, and Microwave, Using Ex Vivo Calf Liver Model

Abstract

Thermal ablation of liver tumors near large blood vessels is affected by the cooling effect of blood flow, leading to incomplete ablation. Hence, we conducted a comparative investigation of heat sink effect in monopolar (MP) and bipolar (BP) radiofrequency ablation (RFA), and microwave (MW) ablation devices.With a perfused calf liver, the ablative performances (volume, mass, density, dimensions), with and without heat sink, were measured. Heat sink was present when the ablative tip of the probes were 8.0 mm close to a major hepatic vein and absent when >30 mm away. Temperatures (T1 and T2) on either side of the hepatic vein near the tip of the probes, heating probe temperature (T3), outlet perfusate temperature (T4), and ablation time were monitored.With or without heat sink, BP radiofrequency ablated a larger volume and mass, compared with MP RFA or MW ablation, with latter device producing the highest density of tissue ablated. MW ablation produced an ellipsoidal shape while radiofrequency devices produced spheres.Percentage heat sink effect in Bipolar radiofrequency : Mono-polar radiofrequency : Microwave was (Volume) 33:41:22; (mass) 23:56:34; (density) 9.0:26:18; and (relative elipscity) 5.8:12.9:1.3, indicating that BP and MW devices were less affected.Percentage heat sink effect on time (minutes) to reach maximum temperature (W) = 13.28:9.2:29.8; time at maximum temperature (X) is 87:66:16.66; temperature difference (Y) between the thermal probes (T3) and the temperature (T1 + T2)/2 on either side of the hepatic vessel was 100:87:20; and temperature difference between the (T1 + T2)/2 and temperature of outlet circulating solution (T4), Z was 20.33:30.23:37.5.MW and BP radiofrequencies were less affected by heat sink while MP RFA was the most affected. With a single ablation, BP radiofrequency ablated a larger volume and mass regardless of heat sink.

A comparison between 915 MHz and 2450 MHz microwave ablation systems for the treatment of small diameter lung metastases

“…Although microwave ablations have been shown to be less susceptible towards the heat-sink effect, its influence on the therapy success is still significant using the current generation of MWA devices (26,27). The significantly higher LTP rate after the ablation of perivascular tumors with both systems confirms these observations.…”

Time-Dependent Impact of Irreversible Electroporation on Pancreas, Liver, Blood Vessels and Nerves: A Systematic Review of Experimental Studies

“…Contrary to thermal ablation techniques, IRE leaves the surrounding tissue intact, causing less collateral damage and thus leading to fewer side effects, less morbidity and a faster recovery[5]. Also, due to the non-thermal electroporation effect, treatment with IRE is not impaired by a heat-sink effect[6] where relatively cool blood flowing in large vessels through the ablation zone prohibits the attainment of effective temperatures around these vessels, leaving viable tumor tissue in situ [7]. Consequently, IRE can be beneficial in the treatment of unresectable tumors or tumors that are not eligible for thermal ablation therapies.…”

Microwave ablation for thyroid nodules: a new string to the bow for percutaneous treatments?

“…Mean volume reduction is the higher among percutaneous techniques: 51-85% (2,15-28). One of the major limits is the heat sink effect, which impacts a lot on high vascularized structures like thyroid parenchyma and thyroid nodules (29). MWA is the more recent percutaneous technique developed.…”