Treatment for medulloblastoma should start within 28 days of surgery (there are some studies which tend towards a worse outcome if RT is delayed beyond this).
Craniospinal RT involves treatment of the whole brain and spine. Craniospinal XRT generally starts first followed by a boost to the posterior fossa.
Some centers using proton therapy to treat the craniospinal axis and this reduces the dose to structures like the thyroid and the cochlea. But the main morbidity of cranial radiotherapy is from the effect of RT on normal brain development.
Whole brain treatment volume –
- Includes the frontal lobe and cribriform plate. Adequate coverage of the frontal lobe and cribriform plate causes superior orbital tissue to be in the field.
- The clinical target volume (CTV) must be at least 0.5 cm below the base of skull –except in the region of the cervical spine when the lower field border has a moving field junction with the superior border of the spinal target volume. This moving upper junction is usually in the mid-cervical spine 5-8 cm below the base of skull.
Whole spine treatment volume –
- The entire thecal sac.
- There is a junction with the inferior border of the cranial target volume
- The field should extend laterally on both sides to cover the recesses of the entire vertebral bodies with at least 1 cm margin on either side.
- The inferior margin should be 2 cm below the termination of the subdural space (S2).
- Sometimes the field is expanded inferiorly to form a “spade shape”. This may more adequately treat disease involving the sacral foramina.
