Definitive Proton Beam Therapy for Second Primary Non-small Cell Lung Cancer After Pneumonectomy.

Purpose: To investigate the outcome of definitive proton beam therapy (PBT) for second primary non-small cell lung cancer after pneumonectomy. Patients and Methods: Between January 2006 and December 2019, 4 patients with second primary lung cancer occurring in the contralateral lung after pneumonectomy were selected from our database of patients who underwent PBT. All patients were men with a median age of 69 (range, 61-79) years at the time of PBT. The median time from pneumonectomy to PBT initiation was 104.5 (range, 92-117) months. All patients had a histology of squamous cell carcinoma and were inoperable due to poor respiratory function. Results: The median survival time was 46.6 (range, 11.7-118.4) months; 3 patients died of their primary disease and one of bacterial pneumonia. The first relapses were local recurrence inside the irradiated field (n = 1) and outside the irradiated field (n = 2) and regional (n = 1). The median time to relapse was 21.5 (range, 6.6-48.1) months. Regarding adverse events, grade 2 pneumonitis occurred in 2 patients, but steroid administration was not required; no grade ≥3 pneumonitis was observed. Conclusion: Definitive PBT for new lesions in the residual lung after pneumonectomy was successful without serious adverse events, although the number of cases was small.