A Phase II Single-Arm Clinical Study to Evaluate the Efficacy and Safety of Carbon Ion Radiotherapy With Atezolizumab and Bevacizumab Combination Therapy in Patients With Advanced Hepatocellular Carcinoma

This clinical trial aims to determine whether adding carbon ion radiotherapy to atezolizumab-bevacizumab therapy improves tumor control and enhances immune response in patients with advanced hepatocellular carcinoma. Over a 3-year study period, eligible patients receiving atezolizumab and bevacizumab who are also suitable for carbon ion radiotherapy will undergo the combined treatment. Clinical outcomes including survival, progression, radiologic response, and toxicity (graded using CTCAE v5.0) will be monitored and assessed.

Inclusion criteria

• Age ≥ 18 years Histologically or radiologically confirmed hepatocellular carcinoma (HCC) Barcelona Clinic Liver Cancer (BCLC) stage B or C, not eligible for curative surgery or transplantation.

At least one measurable lesion according to RECIST criteria. Eligible for treatment with atezolizumab plus bevacizumab based on clinical judgment.

Candidate for carbon ion radiotherapy determined by radiation oncologist. Child-Pugh class A liver function Eastern Cooperative Oncology Group (ECOG) performance status 0-1

Adequate organ and marrow function, including:

Absolute neutrophil count ≥ 1,500/μL Platelet count ≥ 75,000/μL Hemoglobin ≥ 8.5 g/dL Serum creatinine ≤ 1.5 × ULN or creatinine clearance ≥ 50 mL/min AST/ALT ≤ 5 × ULN Total bilirubin ≤ 3 mg/dL No uncontrolled esophageal or gastric varices, confirmed by endoscopy (within 6 months), or adequately treated before enrollment.

Ability to understand and willingness to sign a written informed consent form.

Exclusion criteria

• Prior systemic therapy with anti-PD-1, anti-PD-L1, or anti-VEGF agents within the past year.

Prior carbon ion radiotherapy to the same anatomical region.

Presence of uncontrolled or severe cardiovascular disease, including:

Recent myocardial infarction (within 6 months) Uncontrolled hypertension NYHA class III-IV heart failure Active or history of autoimmune disease requiring systemic immunosuppressive therapy.

Active infection, including:

Uncontrolled bacterial, viral, or fungal infection Active tuberculosis HIV infection, or active hepatitis B/C with uncontrolled viral replication.

Significant bleeding risk, including:

Active gastrointestinal bleeding Untreated or high-risk varices Coagulopathy not controllable with standard therapy Portal vein tumor thrombosis (PVTT) of grade Vp4 if judged unsuitable for treatment by investigator.

Pregnant or breastfeeding women History of organ transplantation, including liver transplantation. Any condition judged by the investigator to interfere with study participation, treatment compliance, or safety evaluation.