How do you differentiate between drug-induced ILD vs radiation pneumonitis in a patient receiving adjuvant T-DXd and adjuvant radiation therapy who develops new pulmonary abnormalities on surveillance imaging?

There are different ways to differentiate between T-DXd-induced ILD and radiation pneumonitis. Radiation pneumonitis is typically confined to the radiation field and has sharp geometric borders, but T-DXd-induced ILD presents with a cryptogenic organizing pneumonia pattern and patchy consolidations ...

Radiation pneumonitis is often confined to the radiation field, whereas pneumonitis related to T-DXd is often bilateral, multifocal, and more diffuse. Timing and treatment response may also help distinguish between the two. Radiation pneumonitis usually occurs in the first 3 months after radiation, ...