Factors Impacting Microwave Ablation Zone Sizes: A Retrospective Analysis

Simple Summary Ablation zone volumes (AZV) following microwave ablation (MWA) for liver tumours exhibit considerable variability, posing challenges for precise therapy planning. In this retrospective analysis, we aimed to identify factors influencing AZV using a specific device designed to restrict the ablation zone past the needle tip. Furthermore, we assessed the efficacy of a 'surgical mode' in expanding the device's application range compared with the conventional 'standard mode'. Notably, the observed AZVs were smaller than the manufacturer's predictions. We found significantly larger AZVs in non-perivascular tumour locations and in hepatocellular carcinoma, compared with metastases. Despite these variations, the use of the 'surgical mode' did not yield significantly larger AZVs compared with the 'standard mode'. These insights contribute to understanding the nuances of AZV and optimising the application of MWA for liver tumours.Abstract Purpose: Evaluation of the influence of intrinsic and extrinsic conditions on ablation zone volumes (AZV) after microwave ablation (MWA). Methods: Retrospective analysis of 38 MWAs of therapy-naive liver tumours performed with the NeuWave PR probe. Ablations were performed either in the 'standard mode' (65 W, 10 min) or in the 'surgical mode' (95 W, 1 min, then 65 W, 10 min). AZV measurements were obtained from contrast-enhanced computed tomography immediately post-ablation. Results: AZVs in the 'standard mode' were smaller than predicted by the manufacturer (length 3.6 +/- 0.6 cm, 23% below 4.7 cm; width 2.7 +/- 0.6, 23% below 3.5 cm). Ablation zone past the tip was limited to 6 mm in 28/32 ablations. Differences in AZV between the 'surgical mode' and 'standard mode' were not significant (15.6 +/- 7.8 mL vs. 13.9 +/- 8.8 mL, p = 0.6). AZVs were significantly larger in case of hepatocellular carcinomas (HCCs) (n = 19) compared to metastasis (n = 19; 17.8 +/- 9.9 mL vs. 10.1 +/- 5.1 mL, p = 0.01) and in non-perivascular tumour location (n = 14) compared to perivascular location (n = 24, 18.7 +/- 10.4 mL vs. 11.7 +/- 6.1 mL, p = 0.012), with both factors remaining significant in two-way analysis of variance (HCC vs. metastasis: p = 0.02; perivascular vs. non-perivascular tumour location: p = 0.044). Conclusion: Larger AZVs can be expected in cases of HCCs compared with metastases and in non-perivascular locations. Using the 'surgical mode' does not increase AZV significantly.