Analysis to a critical state of thermal field in microwave ablation of liver cancer influenced by large vessels

Transapical intramyocardial septal microwave ablation in treatment of hypertrophic obstructive cardiomyopathy: 12-month outcomes of a swine model

BACKGROUND

To date, the extended Morrow procedure is considered the gold standard treatment for patients with obstructive hypertrophic cardiomyopathy who experience severe symptoms and are unresponsive to medication treatment. We therefore aimed to perform transapical intramyocardial septal microwave ablation to reduce the thickness of the interventricular septum myocardium in a minimally invasive method.

METHODS

Fourteen swine were divided to form either a microwave ablation group (n = 7) or a sham group (n = 7). In the microwave ablation group, a transapical microwave antenna was inserted into the septum to ablate each myocardial segment at 40 W for 1 min, while in the sham group, the same operation was performed but without power output. We used echocardiography, electrocardiogram, during the operation. And added computerized tomography, cardiac nuclear magnetic resonance during follow-up.

RESULTS

Segment hypokinesis was observed in all swine immediately following ablation. Compared with the sham group, the thickness of ablated segments in the ablation group decreased significantly 1 month post-operation (ablation group, 5.53 ± 1.00 mm vs. 8.03 ± 1.15 mm, respectively, P < 0.01; sham group, 8.40 ± 0.94 mm vs. 8.21 ± 1.09 mm, respectively, P = 0.081), and the outcome was still observed 1 year post-operation (ablation group, 3.36 ± 0.85 mm vs. 8.03 ± 1.15 mm, respectively, P < 0.01). No perforation of the septum was observed during the procedure or follow-up, and no heart failure or sudden cardiac death occurred during postoperative feeding.

CONCLUSIONS

Transapical intramyocardial septal microwave ablation can effectively and safely produce a large region of necrosis. This technique can potentially mimic surgical myectomy while avoiding cardiopulmonary bypass and median sternotomy in high-risk hypertrophic obstructive cardiomyopathy patients.

Learning curve of microwave ablation for liver cancers

PURPOSE

To evaluate MWA efficacy and safety by cumulative MWA volume and interventional experience.

METHOD

3113 primary liver cancers treated by 7 operators between 2006 and 2018 were studied. Conditional logistic regression was used to estimate within-operators effects of increasing cumulative MWA volume per year on major complication, technical efficacy (TE) and local tumor progression (LTP) rates were adjusted for treatment-level characteristics. Changes were also evaluated by subgroups of tumor size and location.

RESULTS

Lower severe complication rate was detected only in higher MWA volume (HR: 0.31, P = 0.02)). TE rates increased with the increase of MWA volume ((100-150 procedures (HR: 0.33, P = 0.00); 150-200 procedures (HR: 0.08, P = 0.00)) per year. Similar results were found in subgroup analysis of interventional experience (5 to < 10 years (HR: 0.10, P = 0.00). MWA volume per year larger than 150 cases could reduce the major complication rate for tumors smaller than 5 cm (HR: 0.21, P = 0.03) and tumors in higher risk location (HR: 0.18, P = 0.03). The increase of MWA volume per year could significantly increase the TE rate in all tumor size, expect for tumors in high-risk location (100-150 procedures (HR:1.12, P = 0.84), 150-200 procedures (HR: 0.14, P = 0.08)).

CONCLUSIONS

Early and intensive performance of MWA procedures would reduce major complication rates regardless of tumor size and tumor location, but could not improve TE rate in high-risk locations.

Computed tomography-guided microwave ablation of perivascular liver metastases from colorectal cancer: a study of the ablation zone, feasibility, and safety

OBJECTIVES

To compare the ablation margins and safety of microwave ablation (MWA) of perivascular versus non-perivascular liver metastases from colorectal cancer (CRC) and to determine the risk factors for local tumor progression (LTP) after perivascular MWA.

METHODS

Between June 2017 and June 2019, 84 metastases were treated: 39 perivascular (<5 mm from a vessel >3 mm), and 46 non-perivascular. Perivascular metastases were treated with either conventional or optimized protocols (maximum power and/or several heating cycles after repositioning the needle regardless of the initial tumor dimensions). The mean diameter of metastases was 15.4 mm (SD: 7.56).

RESULTS

Vascular proximity did not result in a significant difference in ablation margins. The technical success rate, primary efficacy, and secondary efficacy were 90%, 66%, and 83%, respectively. Perivascular location was not a risk factor for time to LTP (p = 0.49), RFS (p = 0.52), or OS (p = 0.54). LTP was statistically related to the presence of a colonic obstruction (p < 0.05), number of metastases at the time of diagnosis (p < 0.05), type of protocol (p < 0.05), ablation margins (p < 0.001) and LTP was proportional to the number of liver resections before MWA (p < 0.05). There was no LTP in tumors ablated with margins over 10 mm. Two grade 4 complications occurred.

CONCLUSION

MWA is an effective and safe treatment for perivascular liver metastases from CRC, provided that satisfactory margins are achieved. A maximalist attitude could be related to better local control.

Fast calculation of 3D radiofrequency ablation zone based on a closed-form solution of heat conduction equation fitted by ex vivo measurements

Fast calculation or simulation of the ablation zone induced by radiofrequency ablation (RFA) has a critical role in hepatic RFA planning and therapy. However, it remains challenging to approximate the ablation zone in real time, especially when more than one probe is involved in one ablation session. This paper presents a novel computational technique to calculate the 3D ablation zone of one probe RFA and two-probe switching RFA. The main idea is to get an approximate solution of the temperature distribution from a simplified Pennes bioheat equation, and further fit the solution to the coagulation measurements on ex vivo porcine liver. With a closed-form solution of temperature distribution, the calculation of the ablation zone is as simple as the commonly used ellipsoidal model, but it allows a more realistic prediction of combined ablation zones with different inter-probe spacing. The new approximation technique could potentially replace the original ellipsoidal model in the intervention planning step.

Enhanced Mechanical Strength, Flexibility, and Shape-Restoring Rate of a Drug-Eluting Shape-Memory Polymer by Incorporation of Supramolecular Cross-Linkers

The purpose of this study is to develop mechanically robust soybean oil and polycaprolactone (PC)-based drug-eluting shape memory polymers (SMPs) containing polyrotaxane (PRX) cross-linkers. Essentially, the dynamic PRX cross-linker-containing methacrylate group is introduced to increase the cross-linking density and flexibility of the SMP to overcome its mechanical limitations. It was confirmed that the elongation and cross-linking density of the PRX-incorporated SMP were increased by 2-4 times compared to neat SMP. In addition, those high mechanical properties of the PRX-incorporated SMP could be maintained after the degradation of the PC by the drug-eluting process.

A study of the sink effect by blood vessels in radiofrequency ablation

The objective of the current work was to study the sink effect in radiofrequency ablation (RFA) caused by a blood vessel located close to an electrode in a two-compartment numerical model, consisting of a spherical tumor embedded in healthy liver tissue. Several blood vessels of different sizes were studied at different distances from the electrode. It was found that when a straight blood vessel, cylindrical in shape, is located parallel to the electrode, the minimum distance for a drop of only 10% in the isothermal treatment volume above 50°C, compared to the model without the blood vessel, varies from 4.49 mm (for a vessel of 2mm in diameter) to 20.02 mm (for a vessel 20mm in diameter). The results can be used as a guideline to clinical practitioners, in order to quickly assess the potential impact of existing blood vessels on the resulting treatment volume.

Percutaneous microwave ablation for hepatocellular carcinoma adjacent to large vessels: a long-term follow-up

PURPOSE

To retrospectively evaluate the effectiveness and safety of ultrasound (US)-guided percutaneous microwave ablation (MWA) in the treatment of hepatocellular carcinoma (HCC) adjacent to large vessels.

MATERIALS AND METHODS

From February 2006 to February 2013, 452 patients with 605 HCC nodules were treated with US-guided percutaneous MWA. Into large vessels group (Group L), 139 patients with 163 lesions (diameter, 1.0-7.0 cm; mean, 2.5±1.1 cm) located less than 5mm away from large vessels were enrolled. And 313 patients with 442 lesions (diameter, 1.0-8.0 cm; mean, 2.5±1.2 cm) located more than 5mm away from hepatic surface, large vessels, gallbladder and gastrointestinal tract were included in control group (Group C). During the ablation, the temperature of marginal ablation tissues was monitored and controlled.

RESULTS

The median follow-up time was 24.5 months (range 2.1-87.7 months) in Group L, and 25.7 months (range 1.6-93.9 months) in Group C. Technical effectiveness was achieved in 157 of 163 (96.3%) tumors in Group L and 429 of 442 (97.1%) tumors in Group C, respectively (p>0.05). The 1-, 3- and 5-year local tumor progression rates and the 1-, 3- and 5-year accumulative survival rates in the two groups have no significantly statistical differences. In addition, no immediate or periprocedural major complications, no delayed complication of vessels or bile ducts injury were found in both of the two groups.

CONCLUSIONS

With strict temperature monitoring, US-guided percutaneous MWA is an efficient and safe technology in treating hepatocellular carcinoma adjacent to large vessels.

Liver metastases in close contact to hepatic veins ablated under vascular exclusion

BACKGROUND

Liver metastases (LM) in close contact to hepatic veins (HV) are a frequent cause of unresectability. Reconstruction of hepatic veins is technically difficult and outcomes are poor. Intra-operative radiofrequency ablation (IRFA) with vascular exclusion (VE) may be a useful approach.

METHODS

Out of 358 patients operated for LM, 22 with LM close to a HV treated by IRFA under VE with at least one year of follow-up were included in this retrospective study. Technical success was evaluated at four months by CT scan of the ablated lesion. Complications; local, hepatic and extra-hepatic recurrence rates, and overall survival are reported.

RESULTS

The median number of metastases was 4.5 [range: 1-12]. Seventeen patients had bilateral metastases. The median size of ablated lesions was 2 cm [range: 1-5.5]. Seven complications occurred (1 Grade 1, 2 Grade 3b and 4 Grade IVa), with no mortality. No recurrence of ablated lesions was detected at four months or during follow-up. Seventeen patients had new or extra-hepatic lesions. Median overall survival for colorectal patients was 40 months 95%CI[17.5-not reached].

CONCLUSIONS

IRFA plus VE for LM in close contact to a HV is a novel approach, appearing to be a safe and effective technique which can extend the applications of liver metastases surgery.

Comparison of microwave ablation and multipolar radiofrequency ablation, both using a pair of internally cooled interstitial applicators: results in ex vivo porcine livers

PURPOSE

To compare the effectiveness of microwave ablation (MWA) and multipolar radiofrequency ablation (RFA) in ex vivo porcine livers, in both cases using a pair of internally cooled interstitial applicators.

MATERIALS AND METHODS

MWA was performed on ex vivo porcine livers (n = 60) using a pair of simultaneously powered, internally cooled shaft interstitial antennae. Four power settings were used: 50 W, 60 W, 70 W and 80 W (n = 15 per setting). Multipolar RFA was also performed on ex vivo porcine livers (n = 30), also using a pair of simultaneously powered, internally cooled shaft interstitial bipolar applicators. This was performed for two applicator types T30 (3 cm length) and T40 (4 cm length) at a manufacturer prescribed power of 60 W and 80 W, respectively (n = 15 per applicator). Spacing between the two probes was 2 cm in all cases. Each power setting was applied for 15 ablations for 10 min each. The long-axis diameter (Dl), short-axis diameter (Ds) and the ratio Ds/Dl for each ablation were measured. Temperature data were recorded at 10 positions. Temperature curves were recorded at 3 locations, as well as the time required for the temperature to rise to 50°C.

RESULTS

Dl and Ds for all the power settings of MWA were significantly larger than that of both kinds of multipolar RFA (P < 0.05). The rates of temperature to rise to 50°C in all the MW ablations power settings were significantly faster than those in both multipolar RF ablations.

CONCLUSION

MWA by the simultaneous application of double antennae may be more advantageous for treating larger liver tumour than multipolar RFA.