Effect of Microwave Ablation Power and Antenna Approach on Tumor Seeding: An Ex Vivo Subcapsular Tumor Model Study

Objective: To evaluate the effects of microwave (MW) power and antenna approach methods on extrahepatic tumor seeding and ablation zone size using an ex vivo subcapsular tumor-mimic model.

Materials and methods: Forty-one subcapsular tumor mimics were prepared by injecting a mixture of contrast media into bovine liver blocks. Ablation was performed using low- and high-power protocols (75 W and 100 W for 4 and 3 minutes, respectively). The antenna approach was assessed in two directions: parallel and perpendicular to the capsule. CT scans were obtained before and after the ablation to detect contrast leakage on the hepatic surface. The presence of leakage, ablation zone size, and the timing of the first popping sound were compared between the two groups.

Results: Five cases of contrast leakage were observed in the low-power group (n = 21) and 17 in the high-power group (n = 20) (23.8% vs. 85.0%, P < 0.001). Contrast leaks were less frequently observed in the low-power protocol compared to the high-power protocol, regardless of the antenna approach (18.2% [2/11] vs. 80.0% [8/10], P = 0.009 for parallel access; 30.0% [3/10] vs. 90.0% [9/10], P = 0.020 for perpendicular access). The timing of the first popping sound was significantly delayed in the low-power group compared to the high-power group (137.7 ± 51.4 s vs. 77.8 ± 31.4 s, P < 0.001). The size of the ablation zone did not differ significantly between the two power groups (P = 0.415). The parallel and perpendicular antenna approaches did not show significant differences in the number of contrast leaks, popping sound timing, or ablation-zone size (P = 0.536, 0.463, and 0.271, respectively).

Conclusion: Low-power MW ablation may be superior to a high-power protocol in reducing the risk of tumor seeding in subcapsular tumors, regardless of the antenna approach.