Fibrosing interstitial lung diseases represent a heterogeneous group of pathologies. The most well-known is idiopathic pulmonary fibrosis (IPF), which, by definition, has a progressive development leading inevitably to the decline of respiratory function, ultimately resulting in respiratory failure. Additionally, there is a broad group of idiopathic and secondary pulmonary fibrosis, among which some may develop a progressive phenotype.[1]

It has been demonstrated that antifibrotic drugs can slow down the decline not only in IPF but also in non-IPF cases. In two clinical trials [2,3], it was shown that Nintedanib, previously used only in treating IPF, was effective in slowing the progression of non-IPF fibrosis with a progressive phenotype. Therefore, Nintedanib has been approved by the European Medicines Agency (EMA) and the Italian Medicines Agency (AIFA) for treating non-IPF fibrosis in cases where a progressive phenotype is demonstrated. To define a progressive phenotype, one of the following conditions must be present within a maximum observation period of 24 months:

• Decline in Forced Vital Capacity (FVC) > 10%
• Decline in FVC 5-9% + progression of radiological findings on High-Resolution Computed Tomography (HRCT)
• Progression of radiological findings on HRCT + worsening of symptoms

Therefore, considerable attention is given to the radiological aspect, and today, the progression of radiological findings is subjectively assessed.

Well-Aerated Lung (WAL) is a parameter already successfully used to predict outcomes in patients hospitalized for COVID-19-associated Acute Respiratory Distress Syndrome (ARDS) [4].

We aim to evaluate the feasibility and reproducibility of computer-assisted quantification of "Well Aerated Lung" (WAL) in assessing lung involvement in patients with non-IPF pulmonary fibrosis. This aims to make the evaluation of radiological progression more objective.