To evaluate the efficacy and safety of a Spirulina-derived product in preventing and treating radiation-induced esophagitis in esophageal cancer patients undergoing intensity-modulated radiotherapy (IMRT).

The goal of this clinical trial is to evaluate the efficacy and safety of a spirulina-derived product in reducing the incidence, duration, and severity of radiation-induced esophagitis in esophageal cancer patients. The study primarily aims to address two questions: (1) whether the spirulina-derived product can effectively prevent and mitigate radiation-induced esophageal injury, and (2) whether its use is associated with adverse events in patients undergoing intensity-modulated radiotherapy (IMRT).

Participants will be instructed to orally administer the spirulina-derived product or placebo solution four times daily, starting from the first day of radiotherapy and continuing throughout the RT course. After each administration, patients must refrain from eating, drinking, or performing oral intake for at least 1 hour to maximize mucosal contact time of the intervention.

The study will compare the spirulina-derived product group with the placebo group to determine the potential benefits of this spirulina-based intervention in preventing and managing radiotherapy-related esophagitis.

Inclusion Criteria:

1. Patients with histopathologically confirmed malignant esophageal tumor and no distant metastasis;
2. Age ≥ 18 years;
3. ECOG (Eastern Cooperative Oncology Group) performance status score ≤ 2;
4. Scheduled to undergo definitive radiotherapy, neoadjuvant radiotherapy, or adjuvant radiotherapy for esophageal cancer;
5. Adequate hepatic, renal, and bone marrow function;
6. Signed informed consent form.

Exclusion Criteria:

1. History of prior thoracic radiotherapy.

2. Known allergy to spirulina or its derivatives, any component of the thermosensitive gel, or having a history of severe allergic predisposition.

3. Presence of esophageal or oral diseases assessed by the investigator before radiotherapy initiation that may affect the analysis of this study's results (e.g., reflux esophagitis, Barrett's esophagus, severe oral infection, recurrent aphthous ulcers, oral lichen planus, etc.).

4. Use of systemic antibacterial or antifungal medications within one week prior to the start of radiotherapy.

5. Planned concurrent use of medications that may exacerbate radiation-induced mucosal injury after radiotherapy initiation (e.g., anti-EGFR monoclonal antibodies, immune checkpoint inhibitors, etc.).

6. Presence of severe underlying diseases of the cardiovascular, pulmonary, hepatic, renal, hematopoietic, or nervous systems (specific criteria for organ dysfunction are detailed in item 7 below), or conditions such as acute infection, uncontrolled autoimmune diseases, poorly controlled diabetes mellitus, etc., which, in the investigator's judgment, may increase study risks or interfere with result analysis.

7. Presence of significant organ dysfunction meeting any of the following criteria:

   • Hemoglobin < 80 g/L;
   • Neutrophil count < 1.0 × 10⁹/L;
   • Platelet count < 80 × 10⁹/L;
   • Serum total bilirubin ≥ 2 times the upper limit of normal (ULN);
   • Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) ≥ 2.5 times ULN;
   • Serum creatinine > 1.5 times ULN.

8. Pregnant or lactating women.

9. History of severe mental illness, alcohol abuse, or drug abuse.

10. Participation in other clinical trials within the past 3 months.

11. Any other condition deemed by the investigator as potentially rendering the subject unsuitable for participation in this study (e.g., extremely poor oral hygiene, poor compliance, etc.).