A comparison between 915 MHz and 2450 MHz microwave ablation systems for the treatment of small diameter lung metastases

PURPOSE We aimed to retrospectively compare the local tumor control rates between low frequency (LF) and high frequency (HF) microwave ablation devices in the treatment of <3 cm lung metastases. METHODS A total of 36 patients (55 tumors) were treated with the LF system (915 MHz) and 30 patients (39 tumors) were treated with the HF system (2450 MHz) between January 2011 and March 2016. Computed tomography (CT) scans performed prior to and 24 hours after the ablation were used to measure the size of the ablation zone and to calculate the ablation margin. The subsequent CTs were used to detect local tumor progression. Possible predictive factors for local progression were analyzed. All patients had a minimum follow-up of 3 months with a median of 13.8 months for the LF group and 11.7 months for the HF group. RESULTS The ablation margin (P = 0.015), blood vessel proximity (P = 0.006), and colorectal origin (P = 0.029) were significantly associated with the local progression rate. The local progression rates were 36.3% for LF ablations and 12.8% for HF ablations. The 6, 12, and 18 months local progres-sion-free survival rates were 79%, 65.2% and 53% for the LF group and 97.1%, 93.7%, and 58.4% for the HF group, with a significant difference between the survival curves (P = 0.048). CONCLUSION HF ablations resulted in larger ablation margins with fewer local progression compared with LF ablations.