Purpose：To observe and evaluate the clinical efficacy and safety of deep-sea fish oil in preventing acute radiation-induced esophagitis (ARIE).

Methods and Materials：A total of 120 patients with esophageal cancer treated with radiotherapy were randomly assigned (1:1) to treatment or control group. In the treatment group, 1g deep-sea fish oil was oral administrated prophylactically twice a day，the control group was blank control. The clinical efficacy of deep-sea fish oil on prevention of ARIE was evaluated by comparing the differences in the occurrence time, the grade and incidence of ARIE. Additionally, the change in nutritional status was also investigated. Hemanalysis, liver function, kidney function changes， and adverse reactions were compared before and after treatment to evaluate the safety of deep-sea fish oil.

Radiotherapy is an important treatment for esophageal cancer, and acute radiation-induced esophagitis (ARIE) is the most common complication during radiotherapy. The present study was conducted to investigate the clinical efficacy of deep-sea fish oil in the prevention and treatment of ARIE, and to evaluate the effects of deep-sea fish oil on patients' nutritional status, quality of life, pain management, and the effect on the treatment. This is a prospective, single-center, randomized controlled clinical study. The present study has been registered in the Chinese Clinical Trials Registry (ChiCTR2200056847). The present study intends to continuously enroll 120 patients with esophageal cancer who are to receive radiotherapy, and randomly divide the enrolled patients into two groups. One group receive treatment of deep-sea fish oil and the other group is blank control. The differences of ARIE occurrence, ARIE degree, pain degree, and the changes of the inflammatory index were compared.

Inclusion Criteria:

1. Age ≥18 years old, ≤70 years old, gender is not limited;
2. Histological or cytological evidence of esophageal, lung, or breast cancer;
3. ECOG score of 0-2, no swallowing pain or severe dysphagia before radiotherapy;
4. Liver and kidney function, bone marrow function and cardiopulmonary function are not contraindicated by radiotherapy and chemotherapy;
5. PG-SGA score <9;
6. Not pregnant or breastfeeding;
7. The subject must understand and sign the informed consent
8. Have reading comprehension ability and can complete the questionnaire with medical assistance;
9. Those who voluntarily participate in the study and sign the informed consent letter in person.

Exclusion Criteria:

1. Prior radiation therapy;
2. Patients with severe underlying diseases, who cannot tolerate radiotherapy and chemotherapy due to severe liver and kidney insufficiency and poor cardiopulmonary function;
3. Pregnant or lactating female patients;
4. Suffering from severe mental illness and poor compliance;
5. Other cases deemed unsuitable for inclusion by the researchers.