title: Impact of radiation technique upon the outcome of treatment for medulloblastoma.
abstract: Craniospinal irradiation (CSI) is an essential component of the therapy of medulloblastoma. Because medulloblastoma disseminates via the cerebrospinal fluid (CSF), CSI technique involves the irradiation of all CSF-bearing areas which are at risk for tumor seeding. Underdosing with radiation because of inadequacies in CSI technique will produce dose "cold spots" which have the potential of serving as a nidus for tumor recurrence. A simple mathematic model of subclinical disease in medulloblastoma based on the available data concerning the radiosensitivity of medulloblastoma cell lines as well as the known clinical dose-response relationships support the hypothesis that for most cases of medulloblastoma, the radiotherapist is working in a range of doses arrayed on the steep portion of the tumor control probability curve. Underdosing of CSF-bearing areas because of technical problems at the junction of the cranial and spinal fields of irradiation, placement of shielding blocks in the cribiform plate-subfrontal region, and/or anatomic errors in the design of the caudal end of the CSI fields may lead to significant risks of tumor relapse. One may debate the necessity of a posterior fossa boost encompassing the entire anatomic posterior fossa rather than the primary tumor volume with a margin. This review critically evaluates the potential impact of CSI technique upon the outcome of treatment for medulloblastoma, and suggests future areas of inquiry.
authors.affiliation: Duke University Medical Center, Durham, NC 27710, USA. Halperin@radonc.duke.edu
authors.forename: E C
authors.initials: EC
authors.lastname: Halperin
mesh_terms: D002528:Cerebellar Neoplasms / Q000532:radiotherapy*; D002555:Cerebrospinal Fluid / Q000528:radiation effects; D003388:Cranial Fossa, Posterior / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008527:Medulloblastoma / Q000532:radiotherapy*; D009364:Neoplasm Recurrence, Local; D013116:Spinal Cord / Q000528:radiation effects; D014407:Tumor Cells, Cultured / Q000528:radiation effects