title: Stereotactic radiosurgery for brain AVMs: role of interobserver variation in target definition on digital subtraction angiography.
abstract: OBJECTIVE
  We evaluated the extent of interobserver variation in contouring arteriovenous malformations (AVMs) on digital subtraction angiography (DSA) with respect to volume, spatial localization, and dosimetry and correlated our findings with the clinical outcome.
  
  
  METHODS
  Thirty-one patients who had undergone radiosurgery for brain AVMs were studied. Six clinicians independently contoured the nidus on the original DSA. As a measure of variation, the ratio between the volumes of agreement and the corresponding encompassing volumes, as well as the absolute positional shift between the individual target volumes were derived. Using the original treatment plan, the dosimetric coverage of the individually contoured volumes with standard collimators was compared with a similar plan using dynamic conformal arcs.
  
  
  RESULTS
  The mean contoured nidus volume was 3.6 +/- 5.6 cm3. The mean agreement ratio was 0.45 +/- 0.18 for all possible pairs of observers. The mean absolute positional shift between individually contoured volumes was 2.8 +/- 2.6 mm. These differences were more marked in previously treated groups and tended to be more pronounced in those with treatment failure. The mean coverage of the individual volumes by the 80% prescription isodose was 88.1% +/- 3.2% using conventional collimators and 78.9% +/- 4.4% using dynamic conformal arcs (p = 0.001).
  
  
  CONCLUSIONS
  Substantial interobserver variations exist when contouring brain AVMs on DSA for the purpose of radiosurgical planning. Such variations may result in underdosage to the AVM and, thereby, contribute to treatment failure. The consequences of contouring variations may increase with the use of more conformal radiosurgical techniques.
authors.affiliation: Department of Neurosurgery, VU University Medical Center, Amsterdam, The Netherlands. dr.buis@vumc.nl
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Buis
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Lagerwaard
authors.forename: Frederik
authors.initials: F
authors.lastname: Barkhof
authors.forename: Clemens M F
authors.initials: CM
authors.lastname: Dirven
authors.forename: Geert J
authors.initials: GJ
authors.lastname: Lycklama
authors.forename: Otto W M
authors.initials: OW
authors.lastname: Meijer
authors.forename: René
authors.initials: R
authors.lastname: van den Berg
authors.forename: Hans A
authors.initials: HA
authors.lastname: Langendijk
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Slotman
authors.forename: W Peter
authors.initials: WP
authors.lastname: Vandertop
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015901:Angiography, Digital Subtraction; D002648:Child; D005260:Female; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D016634:Radiosurgery; D016896:Treatment Outcome