Evaluation of Probe Angles for Synchronous Waveform 915-MHz Microwave Ablation

The purpose of this study is to compare the ablation performance between a synchronous microwave ablation (MWA) system and a commercially available asynchronous system in ex vivo bovine liver and evaluate the efficacy of ablation at varying entrance angles.

Two 915-MHz MWA systems were used in bench top ex vivo bovine livers with various conditions (synchronous versus asynchronous). Using synchronous technology ablations to liver, kidney, or lung at angles of 0, 15, 30, and 90° were evaluated.

Synchronous and asynchronous MWA systems created mean ablation zone volumes of 26.4 and 15.8 cm³, 62.9 and 45.4 cm³, 90.8 and 56.4, and 75.7 and 54.8 cm³ with single, double (2 microwave probes in use simultaneous) (2 cm spacing), and triple (three probes in use simultaneously) (2 cm and 3 cm spacing) antennae configurations, respectively; adjusted P-values ≤ 0.006. Ablation defects were similar across all groups when evaluated for entrance angle. Specifically, when comparing 0-degree angle to all other angles, achieved zones of ablation (ZA) were similar (mean ± standard deviation for 0-degree versus all other angles: 8.72 ± 4.84 versus 9.38 ± 4.11 cm², P = 0.75). The use of the long-tip probe resulted in a statistically significant increase in the achieved ZA when compared to the short tip probe (10.9 ± 4.3 versus 6.5 ± 2.4, respectively; P = 0.01).

Newly developed synchronous microwave technology creates significantly larger ablation zones when compared to an existing asynchronous commercially available system. The angle of approach does not affect the resulting ZA. This is clinically relevant as true 0-degree angle is often difficult to obtain.