Pneumonitis — inflammation of the lung tissue — is one of the most common and serious complications in treating locally advanced non-small cell lung cancer (NSCLC). Patients typically receive concurrent chemoradiation followed by the immune checkpoint inhibitor durvalumab, and both treatments can independently or jointly trigger pneumonitis. Radiation pneumonitis (RP) usually appears 1–6 months after radiation ends, while checkpoint inhibitor pneumonitis (CIP) can affect any part of the lung and tends to be more diffuse and unpredictable.

Figuring out which type a patient has — or whether it's both — is clinically important, especially when deciding whether to rechallenge with immunotherapy. Comparing current CT scans against the original radiation treatment plan can help the multidisciplinary team determine if the inflammation is confined to the irradiated zone (suggesting RP) or more widespread (suggesting CIP). The later pneumonitis appears after durvalumab starts, the more likely it's CIP — and the less appropriate rechallenge becomes.

Key Takeaways:

• Grade 1 (asymptomatic) pneumonitis requires no treatment; symptomatic cases call for oral corticosteroids (0.5–1 mg/kg/day), tapered slowly over 4–6 weeks
• Grades 3–4 pneumonitis warrants hospitalization, IV steroids, and supplemental oxygen; durvalumab should be discontinued
• Radiation dose constraints (lung V20 <30%, mean lung dose <18 Gy) are recommended to reduce pneumonitis risk when immunotherapy follows

Why it matters: As chemoradiation plus durvalumab becomes the standard of care for locally advanced NSCLC, pneumonitis is an increasingly common clinical challenge. Early recognition, accurate attribution, and prompt management can prevent life-threatening complications and preserve patients' treatment options.