Radiomics analysis
The available staging CT imaging data were manually retrieved from the institutional Picture archiving and communication system (PACS) system and anonymized according to study protocol before being analyzed by the Fondazione Policlinico Universitario “A. Gemelli” Radiomics lab of Rome, Italy. Images were reviewed by two experienced pediatric radiologists in consensus (PLD and DC) for quality check and NB were manually contoured in their entire extension, defining a single region of interest (ROI) per lesion on Eclipse Treatment Planning System (Varian Medical Systems, Palo Alto, CA, USA). In figure 1 is shown an example of NB lesion segmentation. All exams were acquired according to standard CT protocols after intravenous administration of iodinated contrast medium [26]. Equilibrium contrast phase was preferred for image segmentation as the enhancement obtained better delineates the main radiological features of NB [26, 27]. A subsequent independent check of the segmentations has been provided by a radiation oncologist belonging to the radiomics analysis team, in order to ensure ROI integrity and anatomical coherence of the segmented volumes. Radiomics features extraction was then performed using the MODDICOM R library, according to the standard recommended by the image biomarker standardisation initiative (IBSI), [16, 28].