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Radiation therapy for the entire CNS axis


Conventional simulation

Modeling of the field to the brain and spinal cord can be done with conventional simulation, but CT-based planning is recommended.

  • The whole brain is irradiated from side to side down to the caudal border of C3 or C4 (depending on shoulder position, see other chapter). It is very important to be precise with adjustment of the field borders in relation to the base of the skull as for total brain irradiation.
  • At the caudal edge of C3 or C4, a juncture is made with the upper dorsal medulla field. The juncture must be planned with a physicist. 
  • Depending on the height of the patient, 1 or 2 medulla fields are given from behind. If there are two fields, there is also a juncture between these in the thoracic column. The juncture is calculated by a physicist and juncture movement must be planned during the simulation.
  • The lower border for the medulla fields must be below the end of the dural sac which is typically at the level of S2.
  • The lateral borders are lateral to the vertebral bodies with 1 cm margins to cover the dural sac where it follows the nerve roots out of the intevertebral foramen in addition to tuning uncertainty and penumbra.  
  • The medulla fields are dosed by depth where the depth is calculated from the dorsal skin surface to the dorsal aspect of the vertebral bodies/ventral limit of the spinal cord. Due to curvature of the vertebral column, the depth will vary according to the level of the vertebral column. It may be very difficult to identify the structures of the vertebrae on the coronal fluoroscopic simulator images. Differences in depth are compensated by filters of varying thickness.  

CT-based simulation 

Dose planning with CT is recommended for radiation to the entire CNS axis. CT uptake saves time for the patient compared to conventional simulation and is therefore considered patient-friendly. Dose planning is also more simple. 

  • A CT scan is taken after immobilization in VacFix® in the prone position with a mask. 
  • The whole brain and spinal canal limited to S2 at minimum toward the legs is modeled as CTV.
  • It is very important to include the extensions of the subarachnoid space, along the cranial nerves at the base of the skull and the dural extensions along the nerve roots in the intevertebral foramina, are well covered.
  • If the whole brain is to have more fractions than the spinal cord, the whole brain down to C3 or C4 must be modeled as a separate CTV for planning these fractions.
  • Check the field limits of the set-up cover the base of the skull well and the lateral limits for the medulla fields are 1 cm outside the vertebral bodies.
  • It may be beneficial to place the isocenter for the upper medulla field relatively high to obtain a geometric, and relatively clean juncture of the lateral fields toward the brain. Moving junctures can then be avoided between the brain and upper medulla field. 
  • Movement of junctures between the medulla fields is performed routinely.

CT dose plan    


Fractionation and total dose depend on multiple factors, among others, the type of lymphoma and which protocol is followed.

For a curative treatment plan, the following are indicated:

  • For lymphoblastic leukemia/ALL, treatment is administered according to study protocols, for example NOPHO in children, preferably 2 Gy x 9-12 to the whole brain and 2 gy x 6-9 to the spinal cord.
  • For other lymphomas and for palliative treatment, fractionation is determined individually.

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