Prospective Study of Proton Therapy for Lung Cancer Patients with Poor Lung Function or Pulmonary Fibrosis

SIMPLE SUMMARY: Underlying lung disease can affect the pulmonary toxicity after radiotherapy for lung cancer, but treatment outcomes after proton beam therapy (PBT) for lung cancer patients with underlying lung disease have been limited to small retrospective studies. In this prospective study, we aimed to assess pulmonary toxicity following PBT for lung cancer with poor lung function or pulmonary fibrosis. We found that idiopathic pulmonary fibrosis (IPF) was associated with severe pulmonary toxicity and poor survival even after PBT, while PBT seems to be a safe treatment modality for lung cancer patients with chronic obstructive pulmonary disease. ABSTRACT: PBT has a unique depth–dose curve with a Bragg peak that enables one to reduce the dose to normal lung tissue. We prospectively enrolled 54 patients with non-small cell lung cancer treated with definitive PBT. The inclusion criteria were forced expiratory volume in 1 s (FEV1) ≤ 1.0 L or FEV1 ≤ 50% of predicted or diffusing capacity of the lungs for carbon monoxide (DLco) ≤ 50%, or pulmonary fibrosis. The primary endpoint was grade ≥ 3 pulmonary toxicity, and secondary endpoints were changes in pulmonary function and quality of life. The median age was 71.5 years (range, 57–87). Fifteen (27.8%) and fourteen (25.9%) patients had IPF and combined pulmonary fibrosis and emphysema, respectively. The median predicted forced vital capacity (FVC), FEV1, and DLco were 77% (range, 42–104%), 66% (range, 31–117%), and 46% (range, 23–94%), respectively. During the follow-up (median, 14.7 months), seven (13.0%) patients experienced grade ≥ 3 pulmonary toxicity. Seven months after the completion of PBT, patients with IPF or non-IPF interstitial lung disease (ILD) experienced a decrease in the FVC but the decrease in DLco was not significant. Under careful monitoring by pulmonologists, PBT could be a useful treatment modality for lung cancer patients with poor lung function or pulmonary fibrosis.