Rationale and Objectives
The objective of this study was to explore the thermal field distribution of cystic lesions undergoing microwave ablation (MWA) and radiofrequency ablation (RFA) using in vitro phantoms.
Materials and Methods
Cyst-mimicking lesions filled with sodium chloride (NaCl) solution in acrylamide phantoms were treated with MWA and RFA in vitro. The radiofrequency electrodes or MWA antennas were implanted in the centers of the artificial cystic lesions. We used temperature fields located 5, 15, and 25 mm from the electrode or the antenna to plot the temperature-rise curves. Solid phantoms without cysts were also fabricated as controls.
Results
The temperature within cysts increased faster and reached a higher maximum temperature during MWA than during RFA, and this result was independent of the NaCl solution concentration. RFA treatment caused the temperatures within the lesion to increase significantly faster in the cysts containing 0.9% NaCl than in those containing 5.0% NaCl. However, the MWA temperature-rise curves were only weakly affected by the ionic concentration. The median temperature difference values between the 5- and 15-mm points were markedly lower in the 0.9% NaCl cyst-mimicking phantom ( P < 0.001) than in the solid phantom after either MWA or RFA.
Conclusions
Our data indicate that MWA is a more effective technique for focal cystic lesions than RFA and has higher overall energy utilization. MWA was also less affected by the ionic concentration of the cystic fluid.
Introduction
Focal cystic lesions (FCLs) are also known as cystic or predominantly cystic neoplastic or parasitic diseases. These lesions include thyroid cysts, renal cysts, pancreatic cysts, and hepatic cystic echinococcosis. Percutaneous treatments have been used to treat these FCLs. The use of percutaneous ethanol injection is a safe and effective therapy for benign thyroid cysts and is recommended by treatment guidelines . Although no relevant suggestions have been proposed for thermal ablation in thyroid cystic lesions, radiofrequency ablation (RFA) is used to treat thyroid cystic lesions and has been found to lead to outcomes similar to those of percutaneous ethanol injection in prior studies . Renal cysts staged as Bosniak III and IV lesions have 16%–100% and 90%–100% risks of developing malignancy, respectively . RFA and microwave ablation (MWA) have been used to treat Bosniak category III or IV cystic renal tumors . Those studies have found that both RFA and MWA are safe and effective. Previous studies of pancreatic cysts have used endoscopic ultrasound-guided ablation with ethanol (and paclitaxel) . However, the complete resolution rate varied from 30% to 70% during long-term follow-up and was related to the ethanol concentration . One study involving the thermal ablation of pancreatic cysts has been reported; that study used RFA in ex vivo cyst models . Currently, puncture, aspiration, injection, and reaspiration (PAIR) is the accepted invasive technique for hepatic cystic echinococcosis . Although RFA has been used for hepatic cystic echinococcosis, the initial attempts were associated with disappointing long-term efficacy and safety profiles .
Both RFA and MWA have been clinically attempted in FCLs. However, no thermal field distributions of FCLs treated with RFA or MWA have been reported. Furthermore, although some studies have reported the comparison of RFA and MWA for focal solid lesions , no studies have compared the ablative effects of two techniques for FCLs. Therefore, we evaluated the thermal distribution using in vitro phantoms treated with RFA and MWA and compared the outcomes.
Materials and Methods
Cyst-mimicking Phantom Fabrication
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TABLE 1
The Reagents Used to Prepare the Tissue-mimicking Gel with a Citrate Buffer Concentration of 0.2 M and pH of 4.3 (1800 mL)
Ingredients Dosage Citric acid monohydrous 44.82 g Sodium citrate tribasic dehydrate 43.15 g Acrylamide 171.00 g N,N-Methylene-bis-acrylamide 9.00 g Glycerol 108.00 mL Deionized water Top up to 1800 mL
Initiator-Activator Pair l -Ascorbic acid 1.80 g 1% FeSO 4 4.50 mL 3% H 2 O 2 5.40 mL
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Solid Phantom Fabrication
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Ablation Systems
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Ablation Experiment
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Statistical Analysis
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Results
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RFA Versus MWA in Solid Phantoms
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RFA Versus MWA in Cyst-mimicking Phantoms
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0.9% NaCl Versus 5.0% NaCl Cyst-mimicking Phantoms
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0.9% NaCl Cyst-mimicking Phantom Versus Solid Phantom
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Discussion
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Conclusions
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