OPTIMIZING THE RADIOLOGICAL APPROACH TO CHILDREN WITH SOFT TISSUE SARCOMA AND OTHER SOLID TUMORS.

Pediatric solid tumors are among the leading causes of malignancies in children, and optimizing radiological approaches is critical for diagnosis and treatment. Current international guidelines attempt to standardize imaging protocols based on factors such as age, tumor size, and cancer type, but gaps remain in defining the roles of various imaging techniques. This thesis investigated the potential role of different radiological techniques, aiming to define new approaches. One of the goals was to assess the diagnostic accuracy of three magnetic resonance (MR) imaging sequences—Turbo Inversion Recovery Magnitude (TIRM), inverted TIRM (iTIRM), and T1-weighted Controlled Aliasing in Parallel Imaging Results in Higher Acceleration (CAIPIRINHA) DIXON with water contrast—for detecting lung metastases in children with sarcoma undergoing 18F-FDG-PET/MR for staging. TIRM demonstrated the highest sensitivity for identifying lung metastases, while iTIRM and T1w sequences exhibited higher specificity. MR imaging appears to offer strong diagnostic performance in assessing pulmonary metastases, providing a radiation-free alternative to computed tomography (CT). In cases of Wilms tumor, the most common pediatric renal cancer, pulmonary relapse occurs in approximately 15% of cases, often months or years after treatment. Due to the limited number of recurrences, understanding the patterns of lung relapse remains challenging. The study aimed to evaluate whether pulmonary relapses detected by CT occurred at the site of the initial metastasis or in a different location. Our findings revealed a high probability of lung relapse occurring at the same site as the initial metastasis. The PhD project also focused on clarifying the role of bone erosion (BE) as a risk factor in children with orbital rhabdomyosarcoma (RMS) included in the European Pediatric Soft Tissue Sarcoma Study Group (EpSSG) protocol. Patients with extensive BE showed worse outcomes, requiring more aggressive treatment, similar to those with parameningeal RMS. For metastatic RMS, this study investigated the outcomes of patients with distant lymph node involvement as the only metastatic site. These patients showed better outcomes than those with other metastatic patterns, with particularly favorable results in fusion-negative cases. In cases of olfactory neuroblastoma (ON) and NUT carcinoma (NC), both rare in pediatric populations, this research highlighted the need for harmonized international guidelines to improve diagnostic and treatment protocols. Finally, radiomic analysis of pediatric soft tissue sarcomas using axial T2w PET/MR images revealed specific features that could serve as biomarkers for tumor grade and histotype, potentially aiding in more precise diagnostic and prognostic assessments. These findings underscore the importance of refining imaging techniques and protocols to improve outcomes in pediatric oncology.