Abstract
Bone cancer is rare in adults, the most affected persons by this disease are young people and children. The common treatments for bone cancer are surgery, chemotherapy, and targeted therapies; however, all of them have side-effects that decrease the patient’s quality of life. Thermotherapy is one of the most promising treatments for bone cancer; its main goal is to increase the tumor temperature to kill cancerous cells. Although some micro-coaxial antennas have been used to treat bone tumors, most of them are designed to treat soft tissue. Therefore, the purpose of this work is to analyze the thermal behavior of four micro-coaxial antennas specifically designed to generate thermal ablation in bone tissue to treat bone tumors, at 2.45 GHz. The proposed antennas were the metal-tip monopole (MTM), the choked metal-tip monopole (CMTM), the double slot (DS) and the choked double slot (CDS). The design and optimization of the antennas by using the Finite Element Method (FEM) allow to predict the optimal antenna dimensions and their performance when they are in contact with the affected biological tissues (bone, muscle, and fat). In the FEM model, a maximum power transmission was selected as the main parameter to choose the optimum antenna design, i.e., a Standing Wave Ratio (SWR) value around 1.2–1.5. The four optimized antennas were constructed and experimentally evaluated. The evaluation was carried out in multilayer phantoms (fat, muscle, cortical, and cancellous bone) and ex vivo porcine tissue at different insertion depths of the antennas. To fully evaluate the antennas performance, the standing wave ratio (SWR), power loss, temperature profiles, and thermal distributions were analyzed. In the experimentation, the four antennas were able to reach ablation temperatures (>60 °C) and the highest reached SWR was 1.7; the MTM (power loss around 16%) and the CDS (power loss around 6.4%) antennas presented the lowest SWR values depending on the antenna insertion depth, either in multilayer tissue phantom or in ex vivo tissue. These proposed antennas allow to obtain ablation temperatures with an input power of 5 W after 5 min of treatment; these values are lower than the ones reported in the literature.
Highlights
In order to correctly focus this research, the following state of the art and basis bibliographical research focused on the antenna design, thermal effects in biological tissues, development of phantoms, and ablation to treat bone tumors, and the medical application, among others, was consulted
An amputation may be necessary if the tumor extraction means the extraction of key nerves, arteries, or muscles that would leave the limb without functionality
specific absorption rate (SAR) pattern is employed as a performance index of MW antenna design in the tumor ablation because electromagnetic energy is converted into thermal energy that heats the tissues [35,36]
Summary
In order to correctly focus this research, the following state of the art and basis bibliographical research focused on the antenna design, thermal effects in biological tissues, development of phantoms, and ablation to treat bone tumors, and the medical application, among others, was consulted. In [29], Trujillo-Romero et al propose a single slot antenna specially designed to treat bone tumors; in [30] a double slot antenna to treat bone tumors was propose; the antenna was modeled, constructed and evaluated in ex vivo porcine bones; the results obtained show a maximum SWR value equal to 1.8 using 10 W as input power per 10 min of treatment reaching ablation temperatures (60–100 ◦C) In both cases, the antennas showed effectivity to treat bone tissue. Four new micro-coaxial antennas, designed for thermal ablation in bone tissue to treat bone tumors are proposed These antennas allow a better matching with tissues and so lower power inputs and time treatment are required. A comparison between the experimentation and the results of the computational models based on the Finite Element Method was carried out
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