[Experimental study on optimal operating parameters setting of radiofrequency thermal ablation in normal ex-swine...

As a non-surgical minimally invasive treatment, percutaneous radiofrequency ablation (PRFA) is widely used to treat hepatocellular carcinoma (HCC). Treatment effect of PRFA depends on extent of ablative zone. Initially, necrosis diameter achieved by RFA in normal ex-swine liver was about 1.4-1.6 cm, but now larger ablative zone can be achieved with recently developed techniques. This study was to explore optimal operating parameters to enlarge ablative zone resulted from a single process, reduce chances of needle seeding via reducing needle insertion times, and improve curative effects.

The first step: mode A, B, and C (starting power was set to 10 W, 50 W, and 90 W, respectively, output power ascended by 10 W/min till ultimate power of 90 W) were adopted to perform ablation on 8,7,7 normal ex-swine livers, respectively, which were processed to be cylinders. The second step: mode A was adopted to perform ablation on 22 ex-swine liver cylinders, the distances between needle tip and grounding pad were set to 3,8,and 13 cm. Characteristics of ablative zones, such as parallel and vertical diameters, isoperimetric ratio, and volume of ablative zones, ablative energy, and time were analyzed.

The average ablative zone achieved by mode A was larger than those achieved by mode B, and C (2.5 cm x 2.7 cm vs. 1.6 cm x 1.8 cm, and 2.0 cm x 1.5 cm, P<0.05); the volume of ablative zone achieved by mode A was larger than those achieved by mode B, and C (10.0 cm(3) vs. 3.1 cm(3), and 2.1 cm(3), P<0.05); the ablative time achieved by mode A was longer than those achieved by mode B, and C (281.9 s vs. 79.4 s, and 61.4 s, P<0.05)u the ablative zones achieved by mode A were much like a pellet. Ablative zone volume was strongly correlated with ablative time, and energy output (R(2)=0.920, and 0.853, P<0.05). When the distances between needle tip and grounding pad were 3, 8, and 13 cm, the achieved ablative zones were 2.5 cm x 2.7 cm, 3.8 cm x 3.4 cm, and 4.9 cm x 4.1 cm, respectively; ablative volumes were 10.0 cm(3), 22.9 cm(3), and 43.3 cm(3), respectively; ablative time were 281.9 s, 495.6 s, and 896.1 s, respectively (P<0.05).

Adopting lower starting power, and slower power ascending speed may enlarge ablative zone. In a certain extent, distance between needle tip and grounding pad may be positively correlated with ablative volume, and needed ablative time; ablative zone volume may be positively correlated with ablative time, and energy output.