Figure 2

Sagittal CT image showing the patient set-up and immobilization for representative patient (patient 10: male, age 9). The window and level of the image was adjusted to visualize the digitally inserted couch top extension (the portion of the couch that is in contact with the patient), foam pad, thermoplastic mask, and plastic head holder. Isocenters for the cranial field(s), upper spine filed, and lower spine field are indicated with blue × and labeled 1, 2, and 3 respectively.