Diagnosis and management of pneumonitis following chemoradiotherapy and immunotherapy in stage III non-small cell lung cancer

Background: In inoperable stage III NSCLC, the standard of care is chemoradiotherapy and adjuvant durvalumab (IO) for 12 months. Pneumonitis is the commonest toxicity leading to discontinuation of IO. A failure to distinguish between expected radiation-induced changes, IO pneumonitis and infection can lead to unnecessary durvalumab discontinuation. We investigated the use of a structured multidisciplinary review of CT-scans, radiation dose distributions and clinical symptoms for the diagnosis of IO pneumonitis. Methods: A retrospective study was conducted at an academic medical center for patients treated for stage III NSCLC with chemoradiotherapy and adjuvant durvalumab between 2018 and 2021. An experienced thoracic radiologist reviewed baseline and follow-up chest CT-scans, systematically scored radiological features suspected for pneumonitis using a published classification system (Veiga C, Radioth Oncol 2018), and had access to screenshots of radiation dose distributions. Next, two experienced thoracic oncologists reviewed each patients’ case record, CT-scans and radiation fields. A final consensus diagnosis incorporating views of expert clinicians and the radiologist was made. Results: Among the 45 included patients, 14/45 (31.1%) had a pneumonitis scored in patient records and durvalumab was discontinued in 11/45 cases (24.4%). Review by the radiologist led to a diagnosis of immune-related pneumonitis only in 6/45 patients (13.3%). Review by pulmonary oncologists led to a diagnosis of immune-related pneumonitis in only 4/45 patients (8.9%). In addition a suspicion of an immune-related pneumonitis was rejected in 3 separate patients (6.7%), after the thoracic oncologists had reviewed the patients' radiation fields. Conclusions: In patients treated using the PACIFIC regimen, multidisciplinary assessment of CT-scans, radiation doses and patient symptoms, resulted in fewer diagnoses of immune-related pneumonitis (8.9%). Our study underscores the challenges in accurately diagnosing either IO-related or radiation pneumonitis in patients undergoing adjuvant immunotherapy after chemoradiotherapy and highlights the need for multidisciplinary review in order to avoid inappropriate cessation of adjuvant IO.