915MHz Microwave Ablation With Cooled-shaft Antennae: Experimental Study Of Computer-simulated Three-dimensional Thermal Field And Clinical Application Study

Purposes:(1) To explore the thermal field distribution of 915MHz microwave ablation(MWA) with cooled-shaft antennae in vivo porcine livers,and to establish the computer-simulated three-dimensional(3D) thermal fields,then correct this thermal field based on the ablated specimens and temperature curves in vivo porcine livers.(2) To evaluate the safety and efficacy of ultrasound(US)-guided percutaneous 915MHz MWA with cooled-shaft antennae for large hepatic tumors.Materials and Methods:1.Experimental study(1) Based on Pennes' formulation of bio-heat transfer,48 pre-designed spots whose temperatures measured by thermal couple were precisely arranged in microwave phantom.According to the slope rates of initial temperature curves,the distributions of specific absorption rate (SAR) of 915MHz microwave in phantom were solved in two quadrants(z＞0 and z＜0).Two-dimensional fitting method was applied in two quadrants. Three-dimensional thermal fields at the power of 60W were simulated by computer calculated by finite element method(FEM).(2) Thermal physical parameters of in vivo porcine liver were applied to the thermal fields in order to obtain the simulated thermal fields in vivo.915MHz cooled-shaft microwave antennae were inserted into porcine livers directly during in vivo experiments,and temperature curves of selected spots were simultaneously recorded by temperature-measuring system.The simulated thermal fields in vivo were contrasted and corrected according to the results of in vivo experiments.(3) Establish the computer-simulated 3D thermal fields model for simultaneous application of two antennae,according to the thermal field of one antenna The in vivo experiments(power outputs,60W600s;inter-antenna distance,2.0cm,2.5cm, 3.0cm) were performed and the results of ablation zone and temperature were recorded.The simulated results were compared with those in vivo experiments. 2.Clinical study(1) On the basis of simulated thermal fields in in vivo porcine liver, we performed the clinical application study of US-guided percutaneous 915MHz MWA for larger hepatic tumors with cooled-shaft antennae.A random control study was performed comparing with 2450MHz MWA.Thirty-nine patients with HCC 4-8cm in diameter undergone US-guided percutaneous MWA with curative intention between January 2007 and January 2009 were randomly divided into two groups,915MHz group(20 cases)and 2450MHz group(19 cases).There was no significant difference in age,tumor size and baseline liver function between the two groups.(2) TACE combining with 915MHz MWA was performed for hepatic tumors larger than 8cm in diameter.Results:1.Experimental study(1) The computer-simulated 3D thermal fields model of 915MHz MWA in phantom with cooled-shaft antennae were acquired.(2) The computer-simulated 3D thermal field's model of 915MHz MWA in in vivo with cooled-shaft antenna was acquired.The simulated three-dimensional thermal fields were coincident with the results in vivo.(3)The computer-simulated three-dimensional thermal field's model for simultaneous application of two antennae was acquired.A larger and no obvious clefts ablation zone was obtained when the inter-antennae distance was 2.5cm,which was approved by computer simulation and by in vivo experiments.2.Clinical study(1) The follow-up periods for the two groups of patients with large hepatocellular carcinoma(HCC) treated by MWA with cooled-shaft antennae were 3-24 months,respectively,with the median follow-up periods of 6 months.Technique effectiveness rates(TER) were 85%(17/20) and 73.7%(14/19) in 915MHz group and in 2450MHz group respectively(p＜0.05).The rates of local tumor progression(LTP) were 15%(3/20) in 915MHz group and 26.3%(5/19) in 2450MHz group according to the follow-up contrast-enhanced imagings respectively(p＜0.05).Fewer number of insertions were required in the 915MHz group(3.69±0.6) than that in the 2450MHz group(4.71±1.61)(p＜0.05).There were no severe immediate complications in two groups.(2) The follow-up periods for the three patients with large HCC(＞8cm in diameter) treated by 915MHz MWA combining with TACE were 1-9 months,and no case of LTP was found.Conclusions:1.Computer-simulated thermal fields of 915MHz MWA in liver experimental study in vivo were accurate and reliable,which could meet the needs of in vivo experiments and clinical treats.2.The simulated 3D thermal fields with two antennae were coincident with the results in in vivo porcine livers.3.A larger ablation zones for simultaneous application of two antennae were obtained when implanted 915MHz MWA were performed in in vivo porcine livers,and a relatively good ablation zone could be shaped when the inner-antennae distance was 2.5cm.4. Ultrasound-guided percutaneous 915MHz MWA for larger HCC with cooled-shaft antennae was safe and effective.This modality may become a promising method for treatment of larger HCC.Compared with 2,450MHz MWA,915MHz MWA yielded higher technical effectiveness rate and lower rate of LTP,and significantly reduced the number of insertions.5.915MHz MWA combining with TACE for treating large HCC(＞8cm in diameter) was safe and effective,which could be used as one of the combined therapy methods for the patients with large HCC.