Effects of a Thermal Accelerant Gel on Microwave Ablation Zone Volumes in Lung: A Porcine Study

Simulation of Image-Guided Microwave Ablation Therapy Using a Digital Twin Computational Model

Emerging computational tools such as healthcare digital twin modeling are enabling the creation of patient-specific surgical planning, including microwave ablation to treat primary and secondary liver cancers. Healthcare digital twins (DTs) are anatomically one-to-one biophysical models constructed from structural, functional, and biomarker-based imaging data to simulate patient-specific therapies and guide clinical decision-making. In microwave ablation (MWA), tissue-specific factors including tissue perfusion, hepatic steatosis, and fibrosis affect therapeutic extent, but current thermal dosing guidelines do not account for these parameters. This study establishes an MR imaging framework to construct three-dimensional biophysical digital twins to predict ablation delivery in livers with 5 levels of fat content in the presence of a tumor. Four microwave antenna placement strategies were considered, and simulated microwave ablations were then performed using 915 MHz and 2450 MHz antennae in Tumor Naïve DTs (control), and Tumor Informed DTs at five grades of steatosis. Across the range of fatty liver steatosis grades, fat content was found to significantly increase ablation volumes by approximately 29-l42% in the Tumor Naïve and 55-60% in the Tumor Informed DTs in 915 MHz and 2450 MHz antenna simulations. The presence of tumor did not significantly affect ablation volumes within the same steatosis grade in 915 MHz simulations, but did significantly increase ablation volumes within mild-, moderate-, and high-fat steatosis grades in 2450 MHz simulations. An analysis of signed distance to agreement for placement strategies suggests that accounting for patient-specific tumor tissue properties significantly impacts ablation forecasting for the preoperative evaluation of ablation zone coverage.

Computational modeling of microwave ablation with thermal accelerants

PURPOSE

To develop a computational model of microwave ablation (MWA) with a thermal accelerant gel and apply the model toward interpreting experimental observations in ex vivo bovine and in vivo porcine liver.

METHODS

A 3D coupled electromagnetic-heat transfer model was implemented to characterize thermal profiles within ex vivo bovine and in vivo porcine liver tissue during MWA with the HeatSYNC thermal accelerant. Measured temperature dependent dielectric and thermal properties of the HeatSYNC gel were applied within the model. Simulated extents of MWA zones and transient temperature profiles were compared against experimental measurements in ex vivo bovine liver. Model predictions of thermal profiles under in vivo conditions in porcine liver were used to analyze thermal ablations observed in prior experiments in porcine liver in vivo.

RESULTS

Measured electrical conductivity of the HeatSYNC gel was ∼83% higher compared to liver at room temperature, with positive linear temperature dependency, indicating increased microwave absorption within HeatSYNC gel compared to tissue. In ex vivo bovine liver, model predicted ablation zone extents of (31.5 × 36) mm with the HeatSYNC, compared to (32.9 ± 2.6 × 40.2 ± 2.3) mm in experiments (volume differences 4 ± 4.1 cm3). Computational models under in vivo conditions in porcine liver suggest approximating the HeatSYNC gel spreading within liver tissue during ablations as a plausible explanation for larger ablation zones observed in prior in vivo studies.

CONCLUSION

Computational models of MWA with thermal accelerants provide insight into the impact of accelerant on MWA, and with further development, could predict ablations with a variety of gel injection sites.

Survival benefit of thermal ablation therapy for patients with stage II-III non-small cell lung cancer: A propensity-matched analysis

Background

Thermal ablation (TA) is considered a safe alternative to surgical resection for the treatment of non-small cell lung cancer (NSCLC). While previous studies have shown that TA is beneficial for stage I NSCLC patients, however, few have reported on TA efficacy in patients with stage II-III NSCLC. The current study investigated the impact of TA on the overall survival (OS) and cancer-specific survival (CSS) of patients with stage II-III NSCLC.

Methods

Data on patients with stage II-III NSCLC who did not undergo surgical resection between 2004 and 2015 were extracted from the Surveillance, Epidemiology, and End Results (SEER) database. Propensity score matching (PSM), Kaplan-Meier survival curves, and Cox regression were used for statistical analyses.

Results

A total of 57,959 stage II-III NSCLC patients who did not undergo surgical resection were included in this study, 261 of whom received TA. Overall, TA was associated with a longer OS (p = 0.035) and CSS (p = 0.005) than non-ablation. After 1:3 PSM, 252 patients receiving TA and 732 patients not receiving ablation were enrolled in the matched cohort. The OS (p = 0.047) and CSS (p = 0.029) remained higher in the TA group than in the non-ablation group after PSM. Cox regression analysis showed that age, sex, primary tumor site, pathological type, tumor size, radiotherapy, chemotherapy, and thermal ablation were independently associated with OS and CSS (p <0.05). Subgroup analysis found that the advantages of TA were more pronounced among individuals ≥70 years of age, with tumor size ≤3.0 cm, or who did not receive radiotherapy.

Conclusion

TA could be an effective alternative treatment for stage II-III NSCLC patients unsuitable for surgical resection, particularly those ≥70 years of age, with tumor size ≤3.0 cm, or who have not received radiotherapy.

Swine models for translational oncological research: an evolving landscape and regulatory considerations

Swine biomedical models have been gaining in popularity over the last decade, particularly for applications in oncology research. Swine models for cancer research include pigs that have severe combined immunodeficiency for xenotransplantation studies, genetically modified swine models which are capable of developing tumors in vivo, as well as normal immunocompetent pigs. In recent years, there has been a low success rate for the approval of new oncological therapeutics in clinical trials. The two leading reasons for these failures are either due to toxicity and safety issues or lack of efficacy. As all therapeutics must be tested within animal models prior to clinical testing, there are opportunities to expand the ability to assess efficacy and toxicity profiles within the preclinical testing phases of new therapeutics. Most preclinical in vivo testing is performed in mice, canines, and non-human primates. However, swine models are an alternative large animal model for cancer research with similarity to human size, genetics, and physiology. Additionally, tumorigenesis pathways are similar between human and pigs in that similar driver mutations are required for transformation. Due to their larger size, the development of orthotopic tumors is easier than in smaller rodent models; additionally, porcine models can be harnessed for testing of new interventional devices and radiological/surgical approaches as well. Taken together, swine are a feasible option for preclinical therapeutic and device testing. The goals of this resource are to provide a broad overview on regulatory processes required for new therapeutics and devices for use in the clinic, cross-species differences in oncological therapeutic responses, as well as to provide an overview of swine oncology models that have been developed that could be used for preclinical testing to fulfill regulatory requirements.

Adjuvant Thermal Accelerant Gel Use Increases Microwave Ablation Zone Temperature in Porcine Liver as Measured by MR Thermometry

PURPOSE

To determine the effects of a thermal accelerant gel on temperature parameters during microwave liver ablation.

MATERIALS AND METHODS

Sixteen consecutive liver ablations were performed in 5 domestic swine under general anesthesia with (n = 8) and without (n = 8) administration of thermal accelerant gel. Ablation zone temperature was assessed by real-time MR thermometry, measured as maximum temperature (T_max) and the volume of tissue ≥ 60°C (V₆₀). Tissue heating rate, ablation zone shape, and thermal energy deposition using the temperature degree-minutes at 43°C (TDM43) index were also measured. Differences between groups were analyzed using generalized mixed modeling with significance set at P = .05.

RESULTS

Mean peak ablation zone temperature was significantly greater with thermal accelerant use (mean T_max, thermal accelerant: 120.0°C, 95% confidence interval [CI] 113.0°C-126.9°C; mean T_max, control: 80.3°C, 95% CI 72.7°C-88.0°C; P < .001), and a significantly larger volume of liver tissue achieved or exceeded 60°C when thermal accelerant was administered (mean V₆₀, thermal accelerant: 22.2 cm³; mean V₆₀, control: 15.9 cm³; P < .001). Significantly greater thermal energy deposition was observed during ablations performed with accelerant (mean TDM43, thermal accelerant: 198.4 min, 95% CI 170.7-230.6 min; mean TDM43, control: 82.8 min, 95% CI 80.5-85.1 min; P < .0001). The rate of tissue heating was significantly greater with thermal accelerant use (thermal accelerant: 5.8 min ± 0.4; control: 10.0 min; P < .001), and accelerant gel ablations demonstrated a more spherical temperature distribution (P = .002).

CONCLUSIONS

Thermal accelerant use is associated with higher microwave ablation zone temperatures, greater thermal energy deposition, and faster and more spherical tissue heating compared with control ablations.