Many new particle therapy centers are now under construction all over the world. In Japan, ten centers (one center with a proton and carbon accelerator, two centers with a carbon accelerator and seven centers with a proton accelerator) are now in service, and four are now preparing for the start of clinical service or under construction as of July 2013. Nearly 20 years have passed since the National Institute for Radiological Sciences (NIRS) in Chiba (Japan), started carbon-ion therapy in 1994. Long-term results of particle therapy, including those on stage I non-small-cell lung cancer (NSCLC), are gradually accumulating. Recently, clinical results of particle therapy with a median follow-up of 51 months for patients with T2a/bN0M0 NSCLC have been published from the Hyogo Ion Beam Medical Center (HIBMC) in Japan; of the 70 patients reported, 43 were treated with proton beams and 27 received carbon-ion therapy . These patients were not randomized, but both proton and carbon-ion therapy plans were made, and either modality that showed superior dose distribution was chosen for treatment. The 4-year overall survival rate was 58% and the 4-year local control rate was 75% (70% for T2a and 84% for T2b). Toxicities were acceptable, with only two cases of grade 3 pulmonary toxicity. There appeared to be no difference in outcome between proton and carbon-ion therapy. For T1 NSCLC, a 3-year overall survival rate of 74% and a 3-year local control rate of 87% were previously reported from the same institution . Clinical outcomes reported from other proton therapy centers are in line with these results, although follow-up data are shorter [3–5]. Published clinical results from NIRS on carbon-ion therapy appear to show slightly higher local control rates, but the patient number is relatively small and follow-up is relatively short [6,7].