Radiation can be directed at tumors, as well as at parts of the body that may be harboring tumor cells. The most common locations in the body that receive radiation to treat childhood brain or spinal cord tumors are:

• The entire tumor and a small amount of healthy tissue around the tumor (called “margins”).
• The primary tumor site. After a tumor is surgically removed, the area where the tumor grew is irradiated (e.g., the posterior fossa in children with ependymoma) to prevent the tumor from returning.
• The entire brain and spinal cord. For example, children with medulloblastoma receive a high dose of radiation to the primary tumor site and a lower dose to the entire brain and spinal cord to kill any cancer cells that may have spread.