Highly Conformal Craniospinal Radiotherapy Techniques Can Underdose the Cranial Clinical Target Volume if Leptomeningeal Extension through Skull Base Exit Foramina is not Contoured.

•Highly conformal techniques can deliver craniospinal radiotherapy for medulloblastoma.•Meninges and cerebrospinal fluid extend through the skull base with cranial nerves.•These structures receive inadequate dose if they are not specifically contoured.•Posterior fossa foramina should be included in the craniospinal clinical target volume.