Safety and Efficacy of Vertebral Body-Sparing Craniospinal Irradiation With Proton Therapy in Pediatric Tumors

• Vertebral Body-Sparing Craniospinal Proton Irradiation (Radiation): Vertebral body-sparing craniospinal irradiation (VBS-CSI) using intensity-modulated proton therapy (IMPT, pencil-beam scanning). The treatment actively restricts radiation dose to the anterior and central regions of thoracolumbar vertebral bodies to preserve active bone marrow and spinal growth potential, while ensuring adequate target coverage for the whole brain and spinal cord. Two dose levels are applied: 23.4 Gy(RBE)/13 fractions or 24 Gy(RBE)/15 fractions and 36 Gy(RBE)/20 fractions.

Primary outcomes

• Incidence of ≥ Grade 3 acute adverse events [Up to 3 months after completion of radiotherapy]: To evaluate the incidence of treatment-related acute adverse events of grade 3 or higher, assessed according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 5.0 (CTCAE v5.0).

Secondary outcomes

• Active Bone Marrow Preservation Rate [Baseline, 3, 6, 12, 24, 36, 48, 60 months]: The proportion of active bone marrow in the vertebral body is calculated by dividing the width of the low-signal area by the total diameter of the vertebral body, which allows a relatively quantitative assessment of the active bone marrow preservation rate.
• Incidence of spinal deformity [Baseline and at 6, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months after treatment completion]: Evaluation is performed using whole-neuraxis MRI or whole-spine anteroposterior and lateral X-ray films. Spinal scoliosis is quantitatively assessed using the Cobb angle measurement method by a radiologist who is blinded to the patient's specific treatment information. The degree of kyphosis is evaluated by assessing the presence of thoracic kyphosis. Additionally, vertebral body change characteristics of the thoracolumbar spine are measured, including the posterior-to-anterior ratio (PARs) of the vertebral body-defined as the ratio of the posterior vertebral body height to the anterior vertebral body height-as well as intervertebral disc height.

Sex: All, ages: 4 Years to 18 Years

Inclusion Criteria:

* The patient's legal guardian voluntarily signs the written informed consent form.
* Age at diagnosis > 3 years and ≤ 18 years.
* Histopathologically confirmed diagnosis of a central nervous system (CNS) tumor.
* Indication for craniospinal irradiation (CSI) confirmed by multidisciplinary team (MDT) discussion.
* Karnofsky Performance Score (KPS) ≥ 80.
* For postoperative patients, complete healing of the surgical incision with no evidence of wound infection or other complications.
* For women of childbearing potential, effective contraception must be used for at least one month prior to screening, and they must commit to continued contraception throughout the study period and for the required time after study completion.

Exclusion Criteria:

* Previous receipt of any form of spinal radiotherapy.
* Previous major spinal surgery for any reason.
* Presence of clinically significant and confirmed spinal deformity at enrollment (e.g., Cobb angle > 10° measured by MRI or X-ray).
* Presence of medical contraindications to proton radiotherapy.
* Presence of any severe, uncontrolled systemic disease (e.g., active infection, severe cardiac, hepatic, renal, or respiratory insufficiency) that, in the investigator's judgment, makes the subject unsuitable for treatment under this protocol.
* Female patients who are pregnant or breastfeeding.
* Presence of any severe cognitive or psychiatric disorder that prevents understanding of or cooperation with study assessments.