## 2 Materials and Methods
### Patient Cohort  
The patient cohort was made up of a subset of patients, confirmed positive for COVID-19 using RT-PCR, admitted to the IRCCS University Hospital of Bologna-Polyclinic Sant'Orsola-Malpighi (IRCCS AOSP), redirected from neighboring hospitals from February 2020 to March 2021 since the authors' Institute is a regional emergency hub capable of managing patients at high risk of SARS-CoV-2 infection [11]. Consequently, the present cohort of hospitalized patients was considered at high risk irrespective of the referring hospital. Chest CT scan findings (radiological and radiomics) and the clinical data available at patient admission were used to develop a predictive model of patient mortality. The inclusion criteria were the following: having a chest CT scan with slice thicknesses of between 1 and 1.25 mm without contrast medium acquired after patient admission and recorded on the RIS-PACS of the IRCCS AOSP associated with radiological findings, and a complete set of clinical baseline information including RT-PCR positivity to COVID-19. When multiple CT scans were available, only that closest to the date of admission was analyzed. The duration of hospitalization is reported in Supplementary Materials Table S1 according to patient outcome as well as period of first diagnosis (first or second wave). Moreover, the days elapsed between the CT scan and the hospitalization date were not statistically significantly different (\(p\)-value = 0.29) using a standard \(t\)-test comparing patients by outcome. The average days of survival were 21 and 14 in the patients hospitalized in the first and second wave, respectively; this difference showed a trend (\(p\)-value = 0.074), indicating that patients with severe disease were better selected during the second wave, albeit with expected improvement in the treatment strategies available over time. The inclusion criteria were fulfilled by 436 patients, i.e., 286 males (65.6%) and 150 females (34.4%). The main patient characteristics and baseline comorbidities are reported in Table 1. The median age was 68.5 (21-99) years; a hypertension status was recorded in 241 patients. Two-hundred and fifty-one had a fever (Temperature \(\geq\) 38\({}^{\circ}\)) at hospital admission. The choice of using this cutoff for fever was based on the variability of body temperature occurring on the day of admission. Information regarding fever and hypertensive state were included in the routine admission procedure and, hence, were available for all patients; however, no additional details were recorded at admission. \begin{table}
\begin{tabular}{c c} \hline \hline
**Variables** & **Median (Min–Max)** \\ \hline
**Age (years)** & 68.5 (21–99) \\ \hline
**Respiratory rate (Breaths/m)** & 20 (10–98) \\ \hline
**Days of hospitalization** & 13 (0.25–99) \\ \hline
**Yes N (\%)–No N (\%)** \\ \hline
**Hypertension** & 241 (55.3%)—195 (44.7\%) \\ \hline
**History of smoking** & 347 (79.5\%)—89 (20.5\%) \\ \hline
**Obesity** & 363 (83.3\%)—73 (16.7\%) \\ \hline
**Sex** & Male 286 (65.6\%)—Female 150 (34.4\%) \\ \hline
**Fever** & 251 (57.6\%)—185 (42.4\%) \\ \hline
**Lung Consolidation** & 225 (51.6\%)—211 (48.4\%) \\ \hline
**Ground Glass Opacity (GGO)** & 382 (87.6\%)—54 (12.4\%) \\ \hline
**Crazy Paving** & 336 (77.1\%)—100 (22.9\%) \\ \hline
**Bilateral involvement** & 403 (92.4\%)—33 (7.6\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Clinical characteristics of the patients as well as the radiological findings obtained upon radiologist inspection of the CT scans. It is also worth noting that the present cohort presented a large prevalence of obese individuals (83%). This could have been a bias as since an estimation of the visceral fat surface and muscular surface obtained with the segmentation software by segmenting a slice at the height of verteba T12 of the thoracic region was available, the authors expected some dependency on body composition to arise from the respective radiomic feature, which allowed much more nuance in patient characterization.