Phase I (Dose-Escalation) Participants in the Phase I cohort will receive preoperative CIRT using a dose-escalation design to identify an optimal tolerated dose. Three dose levels are evaluated-32.0, 34.0, and 36.0 GyE/8 fractions-delivered in 2 weeks (4 fr/week). Surgical resection is performed 6-8 weeks after CIRT, followed by postoperative evaluation of wound healing, toxicity, and surgical outcomes.

Phase II (Feasibility and Safety Evaluation) All enrolled patients will receive preoperative CIRT at the optimal dose determined in Phase I. The regimen consists of 8 fractions (4 fr/week), followed by surgical resection 6-8 weeks later. Postoperative assessments focus on feasibility and safety, particularly grade 3-5 wound complications within 120 days after surgery. Secondary analyses include pathological response, R0 resection rate, local control, survival, and quality of life. Participants are followed for at least 12 months to assess long-term safety and efficacy.

Participants receive preoperative CIRT as the investigational intervention, delivered in 8 fractions, once daily, four times per week. In Phase I, three dose levels (DL1: 32.0 GyE, DL2: 34.0 GyE, DL3: 36.0 GyE) are evaluated using a 3+3 dose-escalation design to determine the recommended Phase II dose (RP2D). Three patients are initially enrolled per dose level, expanded to six if dose-limiting toxicities occur. In Phase II, all participants receive CIRT at the RP2D following a Simon's two-stage design (Stage I: 20 patients; Stage II: 22 additional if criteria met). Treatment uses fixed-beam or rotating gantry techniques. Post-treatment imaging (CT or MRI) is performed 4-6 weeks after CIRT, followed by surgical resection 6-8 weeks post-radiotherapy. All participants are followed for at least 12 months after surgery to assess postoperative wound complications, treatment completion, and overall outcomes.

To evaluate the safety and tolerability of preoperative CIRT and identify the optimal tolerated dose level. DLTs are defined as grade ≥3 toxicities, including severe wound complications, prolonged hospitalization, or significant treatment delay, assessed according to CTCAE version 5.0.

To determine the clinical feasibility and safety of completing preoperative CIRT followed by surgical resection without major wound-healing complications or treatment-related serious adverse events (SAEs). The endpoint represents the proportion of patients achieving treatment completion without grade 3-5 wound complications or other SAEs within 120 days postoperatively.

To record and grade all acute adverse events associated with preoperative carbon-ion radiotherapy using CTCAE v5.0 criteria to characterize the overall safety profile at each dose level.