Hepatic Thermal Ablation: Effect of Device and Heating Parameters on Local Tissue Reactions and Distant Tumor Growth

Abstract

Purpose To determine whether variable hepatic microwave ablation (MWA) can induce local inflammation and distant pro-oncogenic effects compared with hepatic radiofrequency ablation (RFA) in an animal model. Materials and Methods In this institutional Animal Care and Use Committee-approved study, F344 rats (150 gm, n = 96) with subcutaneous R3230 breast adenocarcinoma tumors had normal non-tumor-bearing liver treated with RFA (70°C × 5 minutes), rapid higher-power MWA (20 W × 15 seconds), slower lower-power MWA (5 W × 2 minutes), or a sham procedure (needle placement without energy) and were sacrificed at 6 hours to 7 days (four time points; six animals per arm per time point). Ablation settings produced 11.4 mm ± 0.8 of coagulation for all groups. Distant tumor growth rates were determined to 7 days after treatment. Liver heat shock protein (HSP) 70 levels (at 72 hours) and macrophages (CD68 at 7 days), tumor proliferative indexes (Ki-67 and CD34 at 7 days), and serum and tissue levels of interleukin 6 (IL-6) at 6 hours, hepatocyte growth factor (HGF) at 72 hours, and vascular endothelial growth factor (VEGF) at 72 hours after ablation were assessed. All data were expressed as means ± standard deviations and were compared by using two-tailed t tests and analysis of variance for selected group comparisons. Linear regression analysis of tumor growth curves was used to determine pre- and posttreatment growth curves on a per-tumor basis. Results At 7 days, hepatic ablations with 5-W MWA and RFA increased distant tumor size compared with 20-W MWA and the sham procedure (5-W MWA: 16.3 mm ± 1.1 and RFA: 16.3 mm ± 0.9 vs sham: 13.6 mm ± 1.3, P < .01, and 20-W MWA: 14.6 mm ± 0.9, P < .05). RFA and 5-W MWA increased postablation tumor growth rates compared with the 20-W MWA and sham arms (preablation growth rates range for all arms: 0.60-0.64 mm/d; postablation: RFA: 0.91 mm/d ± 0.11, 5-W MWA: 0.91 mm/d ± 0.14, P < .01 vs pretreatment; 20-W MWA: 0.69 mm/d ± 0.07, sham: 0.56 mm/d ± 1.15; P = .48 and .65, respectively). Tumor proliferation (Ki-67 percentage) was increased for 5-W MWA (82% ± 5) and RFA (79% ± 5), followed by 20-W MWA (65% ± 2), compared with sham (49% ± 5, P < .01). Likewise, distant tumor microvascular density was greater for 5-W MWA and RFA (P < .01 vs 20-W MWA and sham). Lower-energy MWA and RFA also resulted in increased HSP 70 expression and macrophages in the periablational rim (P < .05). Last, IL-6, HGF, and VEGF elevations were seen in 5-W MWA and RFA compared with 20-W MWA and sham (P < .05). Conclusion Although hepatic MWA can incite periablational inflammation and increased distant tumor growth similar to RFA in an animal tumor model, higher-power, faster heating protocols may potentially mitigate such undesired effects. RSNA, 2016.

Radiofrequency Ablation and Microwave Ablation in Liver Tumors: An Update

“…Generally, RFA is a safe, well‐tolerated, effective treatment for unresectable hepatic malignancies with a dimeter <6.0 cm . Velez et al assessed the safety and efficacy of ablative therapies in preclinical study on F344 rats (150 g, n = 96) with subcutaneous R3230 breast adenocarcinoma tumors, testing the device effect and heating parameters on local tissue reactions and distant tumor growth . They evaluated RFA (70°C for 5 minutes), rapid higher‐power MWA (20 W for 15 seconds), slower lower‐power MWA (5 W for 2 minutes), or a sham procedure (needle placement without energy).…”

A Comparative Study of Ablation Boundary Sharpness After Percutaneous Radiofrequency, Cryo-, Microwave, and Irreversible Electroporation Ablation in Normal Swine Liver and Kidneys

“…Following image-guided ablation procedures, evaluation of the region of cytotoxic treatment zone and the ablation margin is typically assessed with post-treatment contrast-enhanced CT imaging [9,10]. Ablated tissue does not enhance after intravenous contrast injection, and is therefore assumed to be successfully treated and undergoing necrosis.…”

“…Transition to viable tissue often appears sharply demarcated, and sometimes is circumscribed by an enhancing rim [11]. This enhancing rim may represent tissue that has been transiently injured but is expected to recover viability [10]. …”

Benign thyroid nodules treatment using percutaneous laser ablation (PLA) and radiofrequency ablation (RFA)

“…On the other hand, energy deployed was significantly higher in the RFA group than in the PLA group. Systemic effects related to the energy delivered through percutaneous ablations have been occasionally reported, and investigated mainly in preclinical study and for liver disease [22][23][24]. Particularly, oncogenesis has been reported as an off-target effect of radiofrequency ablation [22][23][24], but clear relationship with different ablative methods, the total deployed energy or time of ablation has not been fully investigated yet.…”

“…Systemic effects related to the energy delivered through percutaneous ablations have been occasionally reported, and investigated mainly in preclinical study and for liver disease [22][23][24]. Particularly, oncogenesis has been reported as an off-target effect of radiofrequency ablation [22][23][24], but clear relationship with different ablative methods, the total deployed energy or time of ablation has not been fully investigated yet. Thus, even though very few data exist on the systemic effects of thermal ablations, this aspect cannot be totally neglected when comparing the effects of different ablative modalities which, as in the present study, show highly different energy deposition profile.…”