Local tumor progression after ultrasound-guided percutaneous microwave ablation of stage T1a renal cell carcinoma: risk factors analysis of 171 tumors.

PURPOSE: To retrospectively review long-term oncologic outcomes after ultrasound (US)-guided percutaneous microwave ablation (MWA) of T1a renal cell carcinoma (RCC) and to identify the incidence and risk factors that predict local tumor progression (LTP) after MWA of RCC. MATERIALS AND METHODS: The present study was approved by the institutional review board. A total of 162 patients with 171 RCC nodules (mean size, 2.6 ± 0.8 cm; range, 0.6-4.0 cm) were treated by MWA between April 2006 and January 2017. The influence of eight factors (age; sex; longest tumor diameter; tumor number, location and pathology type; ablation power and time) affecting the risk of LTP was assessed. Univariate Kaplan-Meier and Cox proportional hazard models were used for statistical analysis. RESULTS: LTP occurred in five patients (5 tumors) after US-guided percutaneous MWA of stage T1a RCC. The overall occurrence of LTP was 2.9% per tumor and 3.0% per patient with a median follow-up of 45.5 months. Among the 162 patients, there were no instances of LTP-related deaths; however, 20 patients died of other diseases. All patients with LTP survived through follow-up. The survival rate of LTP-free patients at 1, 3 and 5 years were 98.7%, 89.5% and 82.1%, respectively (p = .38). Univariate and multivariate analysis identified tumor location to be the only independent predictor of LTP. CONCLUSIONS: US-guided percutaneous MWA for T1a RCC achieved a relatively low LTP incidence rate. Tumors adjacent to the renal pelvis or bowel increased the potential of LTP occurrence.

The in vivo performance of a novel thermal accelerant agent used for augmentation of microwave energy delivery within biologic tissues during image-guided thermal ablation: a porcine study.

OBJECTIVES: To investigate the effects of a novel caesium-based thermal accelerant (TA) agent on ablation zone volumes following in vivo microwave ablation of porcine liver and skeletal muscle, and to correlate the effects of TA with target organ perfusion. MATERIALS AND METHODS: This prospective study was performed following institutional animal care and use committee approval. Microwave ablation was performed in liver and resting skeletal muscle in eight Sus scrofa domesticus swine following administration of TA at concentrations of 0 mg/mL (control), 100 mg/mL and 250 mg/mL. Treated tissues were explanted and stained with triphenyltetrazolium chloride (TTC) for quantification of ablation zone volumes, which were compared between TA and control conditions. Hematoxylin and eosin (H&E) staining was also performed for histologic analysis. General mixed modelling with a log-normal distribution was used for all quantitative comparisons (p = 0.05). RESULTS: A total of 28 ablations were performed in the liver and 18 in the skeletal muscle. The use of TA significantly increased ablation zone volumes in a dose-dependent manner in both the porcine muscle and liver (p < 0.01). Both the absolute mean ablation zone volume and percentage increase in ablation zone volume were greater in the resting skeletal muscle than in the liver. In one swine, a qualitative mitigation of heat sink effects was observed by TTC and H&E staining. Non-lethal polymorphic ventricular tachycardia was identified in one swine, treated with intravenous amiodarone. CONCLUSIONS: The use of a novel TA agent significantly increased mean ablation zone volumes following microwave ablation using a porcine model. The relationship between TA administration and ablation size was dose-dependent and inversely proportional to the degree of target organ perfusion, and a qualitative reduction in heat-sink effects was observed.

Evaluation of a Novel Thermal Accelerant for Augmentation of Microwave Energy during Image-guided Tumor Ablation.

The primary challenge in thermal ablation of liver tumors (e.g. hepatocellular carcinoma and hepatic colorectal cancer) is the relatively high recurrence rate (~30%) for which incomplete ablation at the periphery of the tumor is the most common reason. In an attempt to overcome this, we have developed a novel thermal accelerant (TA) agent capable of augmenting microwave energy from a distance normally unattainable by a single microwave ablation antenna. This cesium-based block co-polymer compound transforms from a liquid to a gel at body temperature and is intrinsically visible by computed tomography. Using an agarose phantom model, herein we demonstrate that both the rate and magnitude of temperature increase during microwave ablation were significantly greater in the presence of TA when compared with controls. These results suggest robust augmentation of microwave energy, and may translate into larger ablation zone volumes within biologic tissues. Further work using in vivo techniques is necessary to confirm these findings.