Association between operability and clinical outcomes in patients with stage I NSCLC treated with carbon-ion radiotherapy: a Japanese National Registry Study (J-CROS-LUNG)

Carbon-ion radiotherapy (CIRT) is a non-surgical treatment option for early-stage non-small cell lung cancer (NSCLC). However, the association between operability and outcomes in real-world CIRT cohorts has not been systematically evaluated. This study aimed to evaluate the association between clinically assessed operability and outcomes in patients with stage I NSCLC treated with CIRT. This multicenter prospective registry study analyzed 231 patients with stage I NSCLC treated with CIRT at five institutions between May 2016 and June 2018. Patients were categorized as operable or inoperable based on multidisciplinary tumor board decisions before CIRT. Patients who could undergo lobectomy were considered operable. Survival outcomes, including overall survival (OS), cause-specific survival (CSS) and progression-free survival (PFS), were analyzed using Kaplan-Meier and Cox proportional hazards models. Local recurrence was evaluated using a competing-risk approach, treating death without prior local recurrence as a competing event. The 5-year OS, CSS and PFS rates were 69.6, 85.6 and 54.8%, respectively. Operable patients showed superior 5-year OS (83.5 vs. 49.1%, P < 0.001), CSS (91.9 vs. 75.0%, P < 0.001) and PFS (66.5 vs. 38.0%, P < 0.001) compared with inoperable patients. The 5-year cumulative incidence of local recurrence was 3.8% in operable patients and 12.1% in inoperable patients (Gray's test, P = 0.008). Clinically assessed operability was associated with outcomes after CIRT and may serve as a useful composite baseline clinical marker when counseling patients, interpreting treatment outcomes and designing future clinical studies.