According to the regular tumor registry statistics in Shanghai, malignant tumors among children in the age group of 1-4 years old have risen from the sixth place in the 1980s to the third place at present, while the age group of 5-14 years old has long risen to the second place, however, due to the improvement and progress of diagnostic means and surgical treatment, radiation therapy and chemotherapy in recent years, the prognosis of malignant tumors in children has improved significantly. The prognosis of childhood malignant tumors has been significantly improved, and the death rate has been reduced by about 50% compared with the past. Unlike adult tumors, the main invasive sites and tissues of childhood tumors include: 1/3 originate from the central nervous system and sympathetic nerves; 1/3 originate from the hematopoietic system; the remaining 1/3 originate from bone tissue, soft tissue and genitourinary system. Most of the tumors occur from immature cells, so they are often predominantly embryonal tumors and sarcomas (about 92%), which are non-epithelial malignant tumors, while adults are predominantly adenocarcinomas and epithelial malignant tumors (about 87%). Therefore, children’s tumors, including the normal tissues surrounding the tumors, are more sensitive to radiation than adults. The frequency of childhood tumors is mostly concentrated in early childhood under 5 years of age. Since childhood is in the growth and development stage, especially for breast children, it is more likely to cause developmental disorders, so the risk of developmental or functional disorders caused by irradiation and the possibility of cancer at the irradiated site after several years should be taken into consideration during radiation therapy. Long-term sequelae are age-related and often manifest after growth arrest in children, so long-term follow-up should be given after radiation therapy. The total radiation dose and each division dose of radiation therapy for children are about 10-20% less than those for adults with similar tumors. Moreover, radiation therapy for children has the following characteristics: the irradiation field in the neck should be set to include both sides of the neck, and the irradiation field in the spine should include the entire width of the vertebral body including the transverse process, so as not to cause neck asymmetry and scoliosis deformity. Another feature is that the issue of immobilization during radiotherapy in children is also important. Generally, patient persuasion, use of immobilization equipment and drug anesthesia methods can be used to ensure the treatment position of children. commonly used drugs are 10% chloral hydrate: 1 ml/per year; phenobarbital 0.01 g/per kg.