title: Radiation tolerance limits of the brainstem.
abstract: OBJECTIVE
  One of the key limitations of gamma knife surgery arises from the radiation safety tolerance limit of the brainstem. The authors conducted an analysis of patients with intra-axial brainstem lesions and documented the incidence of adverse radiation imaging effects (ARIE) and new neurological deficits after gamma knife surgery.
  
  
  METHODS
  Thirty-eight patients (39 lesions) with intra-axial brainstem astrocytomas or vascular malformations underwent gamma knife surgery during a 6-year interval. Brainstem exposure volume was calculated by subtracting the volume within the 12-Gy isodose line (12 Gray volume) from the prescription volume. ARIE was defined as a new parenchymal signal alteration on follow-up magnetic resonance imaging sequences.
  
  
  RESULTS
  The average prescription volume was 1.46 cm, 12 Gy volume was 2.03 cm, and brainstem exposure volume was 0.57 cm. Seven (18.4%) patients developed ARIE. ARIE correlated only with the presence of new neurological deficits and age younger than 40 years. Three (7.9%) patients developed minor residual deficits without any ARIE. There was no mortality.
  
  
  CONCLUSIONS
  Exposure of the brainstem to more than 12 Gy at volumes as low as 0.1 cm can produce ARIE and new neurological deficits. The tolerance of the brainstem to radiosurgery is related to patient age, lesion volume, and pathology. Analysis of the exposed volume of brainstem tissue may be useful in radiosurgical planning for individual patients.
authors.affiliation: Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Manish S
authors.initials: MS
authors.lastname: Sharma
authors.forename: Douglas
authors.initials: D
authors.lastname: Kondziolka
authors.forename: Aftaab
authors.initials: A
authors.lastname: Khan
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Kano
authors.forename: Ajay
authors.initials: A
authors.lastname: Niranjan
authors.forename: John C
authors.initials: JC
authors.lastname: Flickinger
authors.forename: L Dade
authors.initials: LD
authors.lastname: Lunsford
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001254:Astrocytoma / Q000601:surgery*; D001933:Brain Stem / Q000473:pathology / Q000528:radiation effects*; D020295:Brain Stem Neoplasms / Q000601:surgery*; D002648:Child; D002675:Child, Preschool; D004307:Dose-Response Relationship, Radiation; D005260:Female; D018303:Ganglioglioma / Q000601:surgery*; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009422:Nervous System Diseases / Q000175:diagnosis / Q000209:etiology*; D011832:Radiation Injuries / Q000175:diagnosis / Q000209:etiology*; D016634:Radiosurgery / Q000009:adverse effects*; D012189:Retrospective Studies; D013997:Time Factors; D055815:Young Adult