Changes in Pulmonary Function Following Single-Fraction Carbon Ion Radiotherapy: A Retrospective Analysis

Background With the increasing incidence of lung cancer and the aging population in Japan, the demand for carbon-ion radiotherapy (CIRT) as a minimally invasive treatment for lung cancer has increased. Although there are reports on pulmonary function after surgery or stereotactic body radiotherapy, the effect of CIRT on pulmonary function remains unclear. We aimed to elucidate the impact of CIRT on pulmonary function and evaluate the safety of CIRT for interstitial pneumonia (IP) by comparing changes in pulmonary function between patients with and without IP. Methods We enrolled 102 patients who underwent single-fraction CIRT (50 Gy [relative biological effectiveness]) for untreated lung cancer (including clinically diagnosed cases) and pre- and post-CIRT pulmonary function tests between June 2011 and November 2017. Clinical factors including dosimetric parameters that affect pulmonary function after CIRT, such as the mean lung dose (MLD) and the percentage of lung volume receiving > 5 Gy (V5) and > 20 Gy (V20), were also evaluated to determine the calculated dose-volume histogram. Results Pulmonary function decreased after CIRT. Comparison between the non-IP and IP groups shows that the respective median rates of change were − 4.91% vs -8.41% for percent predicted vital capacity ( p  = 0.007), -4.35% vs -9.90% for percent predicted force vital capacity ( p  = 0.036), -6.31% vs -10.5% for percent predicted forced expiratory volume in 1 s ( p  = 0.035), and − 4.51% vs -9.93% for percent predicted diffusing capacity of the lung for carbon monoxide (%DLCO) ( p  = 0.083). Significant weak negative correlations were observed among the rates of change in %DLCO, V20 ( p  = 0.012), and MLD ( p  = 0.023). Conclusions Pulmonary function declined after CIRT. This decline was more pronounced in patients with IP than in those without IP.