# Co-Adjuvant Nanoparticles for Radiotherapy Treatments of Oncological Diseases
## 1 Introduction  
Today, cancer is still one of the greatest global causes of death. In 2018, there were 18.1 million new cases and 9.5 million cancer-related deaths worldwide. By 2040, the number of new cancer cases per year is expected to rise to 29.5 million with an estimation of cancer-related deaths close to 16.4 million [1, 2]. Currently, regular screening and surveillance programs required for early diagnosis/intervention are the best ways to improve the outcome and survival. The diagnostic tools in use in healthcare rely on imaging methods, like optical imaging, radiography, magnetic resonance imaging (MRI), and computed tomography (CT), as well as nuclear imaging techniques [3, 4]. More recently image-guided cancer treatments and molecular diagnostics have enabled to subcategorize each cancer type allowing efficient intervention with targeted therapeutics [5, 6]. Over the last years, ceaseless efforts have been put by the scientific and medical communities in the cancer research with the aim of finding new diagnosis alternatives for the fabrication of simpler, broad use, and cost-effective imaging tools and scanners [7, 8, 9]. The most important goal is to surpass the typical drawbacks of conventional diagnostic procedures, which are, for instance, related to the choice among the available contrast agents presenting low accuracy and specificity, short half-life, low radiodensity, and rapid clearance [10, 11]. These disadvantages result in the need of massive and prolonged exposure to high levelsof electromagnetic radiation of the patient for the collection of images with satisfactory resolution [12; 13]. Conventional cancer treatments are chemotherapy, radiotherapy, and surgery. Despite, in the past years, these consolidate procedures have enabled an active fight against cancer ensuring long-term survival and quality of life for several malignancies in oncological patients, their broad use has been always associated to diverse drawbacks and side effects. One of the main problems of chemotherapy is the low specificity of chemotherapeutic drugs for cancer cells. Chemotherapy suffers from non-specific biodistribution and poor tumor accumulation of the therapeutic drugs, resulting in high toxicity, damages of the healthy cells, as well as systemic side effects [14; 15]. Surgery can represent the only potentially curative therapy of high-risk patients. However, the high tumors recurrence rate associated with surgical resection as single oncological protocol is responsible for a significant morbidity and failure percentage in many malignancies [16]. Lastly, the radiation therapy is limited by the maximum cumulative radiation dose allowed without incurring significant injuries to the adjacent tissues or organs [17; 18]. More recently, small molecules-based therapies and immuno-oncology have been demonstrated to be effective owing to some recent successes in the clinic [19; 20]. Besides the monotherapies, the combination of the established and accessible therapeutic protocols with immunotherapy has been validated to be efficient in cancer patients [21; 22]; however, the ability of the molecular agents used in immunological therapies to reduce immune suppression, or to enhance activation of cytotoxic processes in the tumor environment is associated to a severe toxicity, whose side effects results under debate [23; 24]. Novel and targeted cancer therapeutic techniques have been recently developed to guarantee effective, efficient, affordable, and less invasive cancer cares to patients [25]. The search of developing tailored treatments for specific oncological demands has found its productive ground in the branch of nanomedicine; in order to visualize the timetable of the scientific efforts boosting the research on nanomedicine, we the proposed, for instance, works and reviews published in the recent twenty years [26; 27; 28; 29; 30; 31; 32]. The European Medicines Agency (EMA) defines nanomedicine as including all applications of nanotechnology and nanoparticles for tumor targeting, imaging, and therapy [27; 33].