Five-Year Survival Outcomes After Carbon-Ion Radiotherapy for Operable Stage I NSCLC: A Japanese National Registry Study (J-CROS-LUNG)

INTRODUCTION: The standard therapy for stage I NSCLC is surgery, but some operable patients refuse this option and instead undergo radiotherapy. Carbon-ion radiotherapy (CIRT) is a type of radiotherapy. The Japanese prospective nationwide registry study on CIRT began in 2016. Here, we analyzed real-world clinical outcomes of CIRT for operable patients with stage I NSCLC. METHODS: All patients with operable stage I NSCLC treated with CIRT in Japan between 2016 and 2018 were enrolled. The dose fractionations for CIRT were selected from several options approved by the Japanese Society for Radiation Oncology. CIRT was delivered to the primary tumor, not to lymph nodes. RESULTS: The median follow-up period was 56 months. Among 136 patients, 117 (86%) had clinical stage IA NSCLC and 19 (14%) had clinical stage IB NSCLC. There were 50 patients (37%) diagnosed clinically without having been diagnosed histologically. Most tumors (97%) were located in the periphery. The 5-year overall survival, cause-specific survival, progression-free survival, and local control rate were 81.8% (95% confidence interval [CI]: 75.1-89.2), 91.2% (95% CI: 86.0-96.8), 65.9% (95% CI: 58.2-74.6), and 95.8% (95% CI: 92.3-99.5), respectively. Multivariate analysis identified age as a significant factor for overall survival (p = 0.018), whereas age and consolidation/tumor ratio (p = 0.010 and p = 0.004) were significant factors for progression-free survival. There was no grade 4 or higher toxicity. Grade 3 radiation pneumonitis occurred in one patient. CONCLUSIONS: This study reports the long-term outcomes of CIRT for operable NSCLC in the real world. CIRT for operable patients has been found to have favorable outcomes, with tolerable toxicity.