The goal of this study is to evaluate the antiemetic efficacy and drug safety of ondansetron orodispersible film in pediatric patients with malignant tumors who received moderate emetic risk radiation induced vomiting, and to formulate reasonable and effective clinical medication regimen for preventing vomiting caused by moderate emetic risk radiation in children with malignant tumor.

Inclusion Criteria:

• Children with malignant tumors diagnosed by histopathology
• Age range: 1-14 years old (calculated from the day of signing the informed consent form)
• Weight >= 8Kg;
• Lansky functional status (LPS) score >= 50 (excluding posterior fossa syndrome)
• Be planned to undergo upper abdominal or craniospinal radiation therapy, and the upper abdominal irradiation should cover the anatomical area from the upper edge of the 11th thoracic vertebra to the lower edge of the third lumbar vertebra
• Radiotherapy is administered once daily, and the fractional dose is 1.8Gy, except for 1.5 Gy for whole abdominal radiotherapy
• The blood routine test must meet the following criteria: ANC >= 1.0 × 10^9/L (after discontinuation of G-CSF), PLT >= 50 × 10^9/L (without drug support or transfusion therapy), HGB >= 80g/L
• Biochemical tests must meet the following standards: total bilirubin <= 1.5 times ULN (upper limit of normal), ALT <= 2.5 times ULN, AST <= 2.5 times ULN, alkaline phosphatase ≤ 1.5 times ULN, serum albumin >= 2.5 g/dL, BUN and CRE <= 1.5 × ULN
• Expected survival period >= 3 months;
• The guardian of the child understands and signs the informed consent form, has good compliance, and cooperates with follow-up.

Exclusion Criteria:

• The nausea and vomiting caused by the surgery have not fully recovered if the subject has undergone a major surgery
• The patient has symptoms of central nervous system tumors such as cerebral edema and requires intervention with adrenal cortex hormones
• Participants who have participated in or are currently participating in other clinical studies within 4 weeks prior to the first use of the investigational drug (calculated based on the time of the last use of the investigational drug for those who have entered the follow-up period)
• Individuals allergic to 5-HT3 receptor antagonists or other excipients
• Joint use of apomorphine
• Congenital QT prolongation syndrome
• Severe gastrointestinal obstruction
• Other observers who affect the efficacy and adverse reactions
• Used other 5-HT3 receptor antagonists in the first 3 days of enrollment
• According to the researchers' assessment, there may be other factors that could force the subjects to terminate the study midway, such as suffering from other serious illnesses (including mental illnesses) that require concurrent treatment, severe abnormal laboratory test values, family or social factors that may affect the safety of the subjects or the collection of experimental data.

The initial data are available on request from the project leaders（344899525@qq.com），upon reasonable request.