Inclusion Criteria:
* Obtain written informed consent before any trial-related procedures are implemented;
* Age 18-80 years;
* ECOG performance status score: 0-2 points;
* Pathologically confirmed esophageal squamous cell carcinoma;
* Locally advanced stage, unresectable or refusing surgery, and stage IV with only extra-regional lymph node metastasis;
* Tolerance of contrast-enhanced MRI;
* Expected survival \> 3 months;
* Adequate organ function; subjects must meet the following laboratory criteria:
* Absolute neutrophil count (ANC) ≥ 1.5 x 10⁹/L;
* Platelet count ≥ 100 × 10⁹/L.
* Hemoglobin \> 9 g/dL;
* Total bilirubin ≤ 1.5 × Upper Limit of Normal (ULN);
* Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN;
* Serum creatinine ≤ 1.5 × ULN and creatinine clearance (calculated using the Cockcroft-Gault formula) ≥ 60 ml/min;
* Good coagulation function, defined as International Normalized Ratio (INR) or Prothrombin Time (PT) ≤ 1.5 times ULN;
* Normal thyroid function, defined as TSH within the normal range. If baseline TSH is outside the normal range, subjects with normal total T3 (or FT3) and FT4 may also be enrolled;
* Cardiac enzyme levels are within the normal range (simple laboratory abnormalities deemed clinically insignificant by the investigator may also be enrolled);
* For female subjects of reproductive age, a urine or serum pregnancy test should be performed within 3 days prior to the first administration of the study drug (day 1 of cycle 1), and the result should be negative. If the urine pregnancy test result cannot be confirmed as negative, a blood pregnancy test is required. Non-reproductive-age women are defined as those who have been postmenopausal for at least 1 year, or have undergone surgical sterilization or hysterectomy;
* If there is a risk of pregnancy, all subjects (regardless of gender) must use contraception with an annual failure rate of less than 1% throughout the treatment period until 120 days after the last administration of the study drug (or 180 days after the last administration of chemotherapy).
Exclusion Criteria:
* Enhanced MRI showing a primary esophageal lesion thickness less than 5 mm and a short diameter lymph node less than 1 cm.
* Severe emphysema, interstitial lung disease, or COPD.
* History of other malignant tumors and chemotherapy within the past 2 years.
* History of chest radiotherapy.
* An active autoimmune disease requiring systemic treatment (e.g., use of disease-modifying drugs, glucocorticoids, or immunosuppressants) within 2 years prior to the first dose. Replacement therapies (e.g., thyroxine, insulin, or physiological glucocorticoids for adrenal or pituitary insufficiency) are not considered systemic treatment.
* Currently receiving systemic glucocorticoid therapy (excluding nasal sprays, inhaled or other routes of topical glucocorticoids) or any other form of immunosuppressive therapy within 7 days prior to the first dose.
Note: Physiological doses of glucocorticoids (≤10 mg/day of prednisone or equivalent) are permitted.
* Known allogeneic organ transplantation (excluding corneal transplantation) or allogeneic hematopoietic stem cell transplantation.
* Known adverse reactions to the study drug. 9) Individuals allergic to the drug or excipients;
* Individuals with a known history of human immunodeficiency virus (HIV) infection (i.e., HIV1/2 antibody positive);
* Untreated active hepatitis B (defined as HBsAg positive with a detected HBV-DNA copy number greater than the upper limit of normal values in the laboratory of their research center); Note: Hepatitis B subjects meeting the following criteria may also be enrolled:
* HBV viral load \<1000 copies/ml (200 IU/ml) before the first dose. Subjects should receive anti-HBV therapy throughout the study chemotherapy treatment to avoid viral reactivation.
* For subjects with anti-HBc (+), HBsAg (-), anti-HBs (-), and HBV viral load (-), prophylactic anti-HBV treatment is not required, but close monitoring for viral reactivation is necessary.
* Subjects with active HCV infection (HCV antibody positive and HCV-RNA level above the detection limit);
* Subjects who received a live vaccine within 30 days prior to the first dose (cycle 1, day 1); Note: Injectable inactivated influenza vaccines for seasonal influenza are permitted within 30 days prior to the first dose; however, intranasal live attenuated influenza vaccines are not permitted.
* Pregnant or lactating women;
* Presence of any serious or uncontrollable systemic disease, such as:
* Significant and symptomatic abnormalities in rhythm, conduction, or morphology on resting electrocardiogram, such as complete left bundle branch block, second-degree or higher heart block, ventricular arrhythmias, or atrial fibrillation;
* Unstable angina, congestive heart failure, or chronic heart failure with a New York Heart Association (NYHA) classification ≥2;
* Any arterial thrombosis, embolism, or ischemia that has occurred within 6 months prior to enrollment in treatment, such as myocardial infarction, unstable angina, cerebrovascular accident, or transient ischemic attack;
* Poorly controlled blood pressure (systolic blood pressure \>140 mmHg, diastolic blood pressure \>140 mmHg).
* History of non-infectious pneumonia requiring glucocorticoid therapy within one year prior to the first dose, or current clinically active interstitial lung disease;
* Active pulmonary tuberculosis;
* Active or uncontrolled infection requiring systemic treatment;
* Clinically active diverticulitis, abdominal abscess, or gastrointestinal obstruction;
* Liver disease such as cirrhosis, decompensated liver disease, or acute or chronic active hepatitis;
* Poorly controlled diabetes (fasting blood glucose (FBG) \> 10 mmol/L);
* Urinalysis showing ≥++ proteinuria, and 24-hour urine protein quantification \> 1.0 g;
* Patients with mental disorders who cannot cooperate with treatment;
* Medical history or disease evidence, treatment or abnormal laboratory test values that may interfere with trial results or prevent full participation of subjects in the study, or other circumstances deemed unsuitable for enrollment by the investigator.
