Purpose: To determine the extent of variable post-ablative inflammatory response in the periablationl tissue when using microwave (MWA), radiofrequency thermal ablation (RFA), and irreversible electroporation (IRE).
Materials and methods: Wild type C57b 9-10 month old mice (n= 27) were anesthetized and subject to laparotomy to enable direct liver ablation. For MWA (n= 27), 10 W were applied for 12 seconds [AMICA MWA system]. RF liver ablation was performed by using a clinical RF coagulator (CC- 1, Cosman Coagulation System; Radionics, Burlington, Mass) 5 minutes and was adjusted to 70°C 6 1, IRE liver ablation was performed by using a clinical IRE generator (Nanoknife; Angiodynamics, Marlborough, Mass). The exposed lobe of the liver was placed between a pair of 10-m diameter circular flat-plate electrodes (Tweezerode 522; BTX, a division of Genetronics, San Diego, Calif) adjusted to 500 V/cm, a 70-sec pulse length, and 90 pulse repetitions.
The mice were sacrificed at day 1, 3, 7, 14, 21 to permit analysis of the dynamic inflammatory changes in the border zone. Activated inflammatory cell populations in the border zone assessed including Polymorphonuclear cells (Ly-6B.2), Macrophages (F480), and Activated Myofibroblasts (αSMA). Additionally, cells Entering G1 Phase (CDC47) were measured, counted and compared among the three methods of ablation in both the periablational and distant regions of the liver.
All data were expressed as means and standard deviations and were compared by using two-tailed t tests and analysis of variance for selected group comparisons.
Results: Overall, the border zone was less extensive in MWA (37 m) (stdev=10.4) than (RF) (82 m) (stdev=8.6), and (IRE )(108 m)(stdev=10.3), (p<0.01). Although similar amounts of activated Myofibroblasts (αSMA) were seen between day 1 and day 7 for the three methods of ablation MWA 2.6-121.6 cells (P<.009), for RF 6.6-113.6 cells (P<.05), for IRE 1.1-27.7 cells (P<.000) respectively, fewer Macrophages (F480) were seen in the inflammatory response between day 14 and day 21 for MWA 16-17 cells and IRE 16-20 compared to RF 40.3-43 (P<.05) for both time points.
Furthermore, there were fewer percentage of hepatocytes cells that entering G1 Phase (CDC47) in MWA (35%) in the distant liver compared to either RF (44%) or IRE (60%).
Conclusion: MWA produces less of an inflammatory response than RF or IRE. Reduced recruitment and activation of these potentially tumorigenic cell populations potentially may lead to a reduced chance to develop distant liver tumor after MWA.
