# Stereotactic Positioning System: Towards a Mechanism Used in Thermal Ablation Therapy
Therefore, the cancer cells either burn or alter their genetic composition, stopping their excessive reproduction [11]. MTA is considered a minimally invasive treatment because the micro-coaxial antennas can be located at a specific point over the tumor utilizing a small percutaneous incision. Ultrasound or computerized tomography are used to guide the antenna inside the tumor. The micro-coaxial antenna generates an electromagnetic field that interacts with the tumor and the healthy tissue. One of the main advantages of thermal ablation to treat cancer is the generation of fewer side effects; moreover, they are more tolerable than those generated by chemotherapy or surgery [10]. The temperature distribution generated by the micro-coaxial antenna is strongly related to the antenna type and location. Thus, one of the main goals in thermal ablation is the correct antenna placement. The antenna must be placed with high accuracy in the target because a slight deviation could cause damage to the surrounded healthy tissue. Therefore, medical images are used to correctly track the antenna location and insert the antenna at the treatment place. According to the American Cancer Society, 1720 cases of bone cancer were prognosticated to be deadly in 2020 [12]. Bone tumors are common in long bones, such as the femur and tibia. The most common treatments are surgery (amputation), radiotherapy, and chemotherapy; however, these treatments develop several side effects in patients. Bone tumors are more common in young people; therefore, new treatments to eradicate the tumor and keep the integrity of the healthy bone have been proposed. Microwave ablation (MWA) is considered a minimally invasive technique to generate coagulative necrosis of the tumor cells by increasing their temperature. In clinical practice, thermal ablation for soft tissue has been widely studied, and its biological action mechanisms have been reported [13; 14; 15; 16; 17]. Therefore, less information has been reported concerning the thermal ablation for bone tumors. The literature describes several clinical studies to treat bone tumors; however, they were implemented using micro-coaxial antennas to treat soft tissue [10; 18; 19; 20; 21]. Recently, micro-coaxial antennas designed to treat primarily bone tumors have been studied [10; 22; 23; 24; 25]. Therefore, new necessities to thoroughly test the antenna's performance have appeared. One of the most important aspects is the antenna location, i.e., it is essential to have a positioning system able to hold and locate the micro-coaxial antenna in the correct place (inside the bone tumor), and the antenna must be located and fixed exactly over the tumor to be treated with microwave thermal ablation. Despite the evolution and multiple applications of stereotactic systems in neurosurgery, no information about its application in thermal ablation using micro-coaxial antennas has been found. The development of stereotactic systems has been maintained mainly for the skull because it is used mainly for neurosurgery, leaving aside different parts of the body. However, the new applications, such as thermal ablation, required stereotactic systems to treat different locations. In particular, bone cancer is prevalent in large bones; therefore, it is necessary to propose a new system that can easily locate a micro-coaxial antenna over the region to be treated, i.e., adopting the upper or lower limbs shape to place the antenna inside the bone tumor and keep the antenna in the same location during the whole treatment time. In this work, a stereotactic positioning system for thermal ablation of bone tumors is introduced [26]. The design, the materials used for its manufacture, and the construction process of the system are presented. In addition, a series of preliminary tests were carried out to evaluate the accuracy of the displacements made by the stereotactic positioning system [26]. Finally, graphical interface was developed to allow the stereotactic system to be controlled by an external user.