High-frequency versus low-frequency microwave ablation in malignant liver tumours: evaluation of local tumour control and survival.

Purpose: To compare local tumour control and survival rates in patients with liver metastases treated with microwave ablation (MWA), using either a low-frequency (LF) (915 MHz) or high-frequency (HF) system (2.45 GHz).
Materials and Methods: The retrospective study included 221 patients (mean age: 61.7 years) with 356 malignant hepatic lesions. Ninety-four patients with 133 lesions underwent LF-MWA between September 2008 and February 2011, while 127 patients with 223 lesions were treated with HF-MWA between March 2011 and July 2013. MRI was performed after 24 h from each procedure and at 3, 6, 9, 12, 18 and 24 months post-ablation. Both groups were compared with the Fisher's exact test. Survival rates were calculated using the Kaplan-Meier test.
Results: The mean initial ablation volume of LF-MWA was nearly half of HF-MWA (19.1 mL vs. 39.9 mL). The difference in volume between both systems was significant (p < .0001). With LF-MWA, 39/133 lesions (29.32%) progressed at follow-up while the number of lesions which progressed with HF-MWA was 10/223 (4.5%). The mean time to progression was 5.03 and 5.31 months for the lesions treated with LF-MWA and HF-MWA, respectively. The difference between both systems was significant (p = .00059). The 1-, 2- and 4-year overall survival rates for curative indication were 98.9%, 95.7% and 82.9% for LF-MWA, respectively, and were 100%, 97.6% and 92.9% for HF-MWA, respectively. The difference in survival rates was not significant (p > .05).
Conclusion: Both LF- and HF-MWA systems are effective treatment options for oligonodular liver malignant lesions, but significantly higher ablation volumes, longer time to progression and lower progression rates were observed in HF-MWA.