## 1 Introduction
Researchers have determined that the temperature between 60 and 100 \({}^{\circ}\)C is the optimal ablative temperature range in order to induce the protein coagulation and reach instantaneous cell death, while the temperature over 100 \({}^{\circ}\)C leads to tissue vaporization and carbonization negatively affecting and decaying the size of ablation area [5]. Thermocouples, magnetic resonance imaging (MRI), and computed tomography imaging (CT) are current accurate temperature measurement techniques exploited during thermal therapies of the tumor by clinicians. However, all the existing techniques have their drawback during temperature measurements such as slow response, poor resolution, high cost, and invasiveness [10]. Fiber optic sensors (FOSs) can be proposed as an alternative to the current measurement techniques offering higher resolution and real-time measurement opportunities. In addition, optical fibers are small, non-toxic, minimally invasive, biocompatible (according to ISO 10993 standard), electromagnetically and chemically inert due to the non-metallic composition, highly flexible, and sensitive [3]. The FOS divided into two sensing methods: fiber Bragg grating (FBG) arrays working on the principle of the wavelength division multiplexing and distributed sensing based on frequency domain reflectometry. In FBG, several sensors are inscribed inside the single fiber providing the sensing mechanism in multiple points. However, the main drawback of the FBG consisted of the distance between multiplexed FBGs array sensors. This work proposes the application of the advanced 16-element array FBGs to overcome the existing limitation and demonstrate the best sensing performance during temperature monitoring over a 7.61 cm sensor length. Moreover, this work investigated the possibility to employ nanoparticles as an approach to achieve homogeneous heat distribution during the thermal ablation process that may prevent the death of healthy cells surrounding the tumor. The widely used type of metallic nanomaterial in RFTA is an iron oxide magnetic nanoparticle (IONP) with a magnetite Fe\({}_{3}\)O\({}_{4}\) core [8; 11]. Nanoparticles are small nanomaterials of size between 1 nm to 100 nm distinguished by their advanced magnetic, optical, and mechanical properties. In addition, magnetic iron oxide nanoparticles are differentiated by their biocompatibility and high surface-to-area ratio leading to the specific and selective attachment to the cancer area by the surface functionalization opportunities. Magnetic nanoparticles are known for the superior control of energy deposition in the cancer area by only heating the targeted area [12]. The thermal ablation of the tumor loaded with iron oxide magnetic nanoparticles and further exposure to the external electromagnetic field lead to the energy conversion into heat. The heat generation occurs due to the friction occurring between nanoparticles and surrounding the medium based on Neel and Brownian relaxation phenomena and the hysteresis loss [12; 13]. The magnetic moment of magnetic nanoparticles subjected to the alternating magnetic field (AMF) tends to line up with the field leading to the dissipation of magnetic energy into thermal energy when the nanoparticles' moment backtracked to the equilibrium [14]. The size of nanoparticles is vital for heat generation and biodistribution within the tissue affecting the possible outcome of thermal therapy. Superparamagnetic nanoparticles with sizes between 10 and 30 nm were found as the best candidate for the temperature increase during ablation. Moreover, the most important parameters of nanoparticles affecting the thermal therapy features are the dispersion concentration and the solvent. The concentration of iron oxide magnetic nanoparticles has a direct relation to the finite sum of generated heat during the treatment. Meanwhile, the dynamic viscosity of the solvent affects the total amount of generated heat by Brownian motion phenomena [12; 15].