## 1 Introduction  
Head and neck cancer is the sixth most common neoplasm in the world [1], with some known risk factors such as smoking, oral health, genetics, and the presence or not of human papilloma virus infection (HPV) [2, 3]. Nevertheless, the presence of HPV has been identified as a good prognostic factor, since HPV-positive cases show a reduction in mortality by 58% and a better response to treatment than HPV-negative patients [2]. This is especially relevant in patients with oropharyngeal cancer, where the latest AJCC classification discriminates according to HPV status, due to its prognostic nature [4]. Diet, ultraviolet radiation, oral health, or genetic predisposition are other risk factors with lower incidence [3]. Despite its high incidence, the survival rate has been increasing in recent years due to early diagnosis and the improvement in therapeutic strategies [1]. Functional images usingPositron Emission Tomography (PET) with \({}^{18}\)F-2-fluorine-2-deoxy-D-glucose ([\({}^{18}\)F]FDG) in combination with computed tomography (CT) are a useful tool to assess the recurrence before the treatment or in the case of relapse thanks to the high negative predictive value [1], especially during the first two years post-treatment due to the high risk of relapse (50-60%) [5; 6] in locoregional advanced oropharyngeal cancer (stage III or IV). [\({}^{18}\)F]FDG PET/CT images help to evaluate efficiently the changes produced in tissues after therapies and treatments, discriminating between active residual disease, recurrent disease, and post-treatment fibrosis. As a result of such high levels of sensibility and specificity, PET-CT findings lead to a change in management for up to 25% of patients [7; 8; 9]. [\({}^{18}\)F]FDG PET images are usually analyzed quantitatively through the Standardized Uptake Value (SUV), which represents the relative radiotracer uptake in the lesion [1]. The [\({}^{18}\)F]FDG uptake in head and neck cancer was evaluated by [PERSON] et al. [2], where lower SUVs were related to greater survival rates and disease control. In addition, the evaluation of volumetric parameters, such as the Metabolic Tumor Volume (MTV) and Total Lesion Glycolysis (TLG), has shown promising results. [PERSON] et al. [3] have demonstrated that higher MTV and TLG are related to tumor recurrence. [PERSON] et al. [10] proved the prognostic effectiveness of [\({}^{18}\)F]FDG PET parameters among patients with head and neck squamous cell cancer. Additionally, [PERSON] et al. [7] demonstrated the prognostic relevance of [\({}^{18}\)F]FDG PET parameters in the context of locally advanced head and neck squamous cell carcinoma. Radiomics is an evolving field that uses a non-invasive methodology to characterize tissues and organs based on a large number of features extracted from the medical images. The underlying hypothesis of radiomics is that genomic cancer subtypes are reflected in image-based features. Subsequently, recent techniques such as textural analysis have demonstrated to be optimal to quantify these cancer phenotype properties [11; 12; 13]. These sub-visual features can be grouped into intensity, shape, and textural relationships between pixels. The textural features, or second order, represent the spatial distribution relationship between voxel intensities, such as the gray level co-occurrence matrix (GLCM), which calculates the correlation between two gray levels at a certain distance and a certain direction in an image. In the last years, the use of radiomics for the analysis of [\({}^{18}\)F]FDG PET/CT images in oncology has increased [8; 11; 14; 15]. In head and neck cancer, intratumoral heterogeneity is considered one of the main factors that influences treatment progression and chemotherapy resistance [16]. Molecular heterogeneity is reflected macroscopically through these textural image features [14]. Consequently, the relationship between genetic and metabolic heterogeneities and its ability of prognosis in [\({}^{18}\)F]FDG PET images was evidenced in recent studies [8; 13; 17; 18; 19; 20].