Outcomes of definitive carbon-ion radiotherapy for cT1bN0M0 esophageal squamous cell carcinoma.

Background: A recent phase I/II study determined the optimal dose of definitive carbon-ion radiotherapy (CIRT) for cT1bN0M0 esophageal cancer. This study aimed to further confirm the efficacy and feasibility of the recommended dose fractionation of CIRT with long-term follow-up results in a larger sample size.

Methods: This single center retrospective study evaluated patients with cT1bN0M0 esophageal squamous cell carcinoma treated with the recommended dose fractionation of 50.4 Gy relative biological effectiveness in 12 fractions, between 2012 and 2022.

Results: Thirty-eight patients underwent CIRT at our hospital. Although eight (21.1%) patients were older than 80 years, 15 (39.5%) had high surgical risk, and seven (18.4%) were at high risk for chemotherapy, all patients underwent CIRT as scheduled. Grade 3 esophagitis occurred in eight (21.1%) patients and grade 3 pneumonia in one (2.6%) patient in this study, but no grade 4 adverse events occurred. The only grade 3 late adverse event was pneumonia in one patient (2.6%). The 5-year overall survival rate, local control rate, and disease-free survival rates were 76.6% (95% CI, 90.9-62.4), 74.9% (95% CI, 90.7-59.0), and 66.4% (95% CI, 83.3-49.5), respectively. Additionally, post CIRT recurrence was as follows: seven (18.4%) patients had recurrence in another part of the esophagus, three (7.9%) in the primary site, three (7.9%) in lymph nodes outside the irradiated area, and one (2.6%) patient had liver metastasis.

Conclusions: Our study demonstrates that CIRT using the recommended dose fractionation is feasible and effective for cT1bN0M0 esophageal squamous cell carcinoma.