# Computer Simulations of Dual-Antenna Microwave Ablation and Comparison to Experimental Measurements
## 1 Introduction  
Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide [1]. The five-year survival rate for HCC is the second lowest after pancreatic cancer. [2]. Hepatic resection surgery, liver transplantation, and ablation therapy are common treatment means of HCC [3]. It is reported that most hepatic tumors are inoperable and only about 25% of patients are suitable for traditional surgical resection [4, 5]. Minimally invasive techniques of liver tumor treatment such as radiofrequency (RF) ablation and microwave ablation (MWA) procedures have a wide range of indications [6]. MWA can be used as a complementary or stand-alone treatment for HCC [7]. Nowadays, CT-based [8] or ultrasound-guided [9] MWA of liver tumors is becoming more widely employed. Most MWA applications are performed with a single antenna. One of the most obvious shortcomings of single-antenna ablation is the small size of the coagulation zone [10]. For small tumors less than 3 cm in diameter, the physician is required to ablate them completely at once [11]. Thus, single-antenna ablation requires a precise puncture. For large tumors more than 5 cm in diameter, there is a continuing need for multi-antenna MWA [12]. To obtain a larger coagulation zone, many studies have been developed as early as 1993 by [PERSON] et al. [13]. It took more than 20 min of simultaneous heating of three to four antennas to achieve the therapeutic effect [14, 15]. [PERSON] et al. [16] calculated the power deposition along a diagonal cross-section within a parallel array of four antennas. However, there were uneven temperatures, a complicated placement process, and a tendency for the position to shift. [PERSON] et al. [17] investigated the effect of parallel and non-parallel antennas on the shape of the coagulation zone. It was found that the 2.45 GHz needle applicator was more susceptible to antenna tip deflection than the 915 MHz antenna. [PERSON] et al. [18]found that the 2.45 GHz antenna could produce a larger coagulation zone more rapidly than the 915 MHz antenna. A dual-slot 2.45 GHz antenna was the best choice for MWA [19]. [PERSON] et al. [20] investigated the multi-pin radiofrequency ablation (RFA) antennas and used a square triangular array of antennas to obtain a larger coagulation zone. Nevertheless, the cross-sectional area of the coagulation zone under application of three applicators was only around 958 mm\({}^{2}\)[20]. [PERSON] et al. [21] investigated the simulation of double 915 MHz antennas in ex vivo bovine livers, to provide the technical basis for treating large liver tumors in one ablation session. There has been an increasing demand for dual-antenna arrays or even multi-antenna MWA. Dual-antenna MWA has been proven to be clinically feasible. With ablation times between 3 and 7 min and a spacing between two antennas of 1 to 2 cm, tumors more than 5 cm in diameter can be treated. The clinical effects are satisfactory [22]. Dual-antenna MWA is always cost-saving and more convenient than multi-antenna (three or four antennas) MWA to both patients and surgeons. Therefore, dual-antennas are widely used in the ablation of large tumors [17]. However, the shortcomings of dual-antenna MWA are low temperatures, long treatment times, and difficult antenna deployment. How to achieve accurate tumor treatment with MWA with two needle applicators deserves further investigation. In this study, in order to systematically analyze the coagulation zone changes of dual-antenna MWA, the simulation model was established and validated by ex vivo experiments. The spacing between two parallel antennas was continuously adjusted and the synchronous heating was kept on. The effects of heating power, dual-antenna spacing, and blood perfusion on the MWA coagulation zone were studied. In addition, the differences between isothermal and Arrhenius models of the coagulation zone were compared.