title: Variability in target delineation for cavernous sinus meningioma and anaplastic astrocytoma in stereotactic radiosurgery with Leksell Gamma Knife Perfexion.
abstract: BACKGROUND
  Radiosurgery clinical practice relays on empirical observations and the experience of the practitioners involved in determining and delineating the target and therefore variability in target delineation might be expected for all the radiosurgery approaches, independent of the technique and the equipment used for delivering the treatment. The main aim of this study was to quantify the variability of target delineation for two radiosurgery targets expected to be difficult to delineate. The secondary aim was to investigate the dosimetric implications with respect to the plan conformity. The primary aim of the study has therefore a very general character, not being bound to one specific radiosurgery technique.
  
  
  METHODS
  Twenty radiosurgery centers were asked to delineate one cavernous sinus meningioma and one astrocytoma and to plan the treatments for Leksell Gamma Knife Perfexion. The analysis of the delineated targets was based on the calculated 50 % agreement volume, AV50. The AV50 was compared to each delineated target by the concordance index and discordance index. The differences in location, size, and shape of the delineated targets were also analyzed using the encompassing volume compared to the common volume, i.e., the AV100, of all delineated structures.
  
  
  RESULTS
  Target delineation led to major differences between the participating centers and therefore the AV50 was small in comparison to each delineated target volume. For meningioma, the AV50 was 5.90 cm(3), the AV100 was 2.60 cm(3), and the encompassing volume was 13.14 cm(3). For astrocytoma, the AV50 was 2.06 cm(3) while the AV100 was extremely small, only 0.05 cm(3), and the encompassing volume was 43.27 cm(3). These variations translate into corresponding discrepancies in plan conformity.
  
  
  CONCLUSIONS
  Significant differences in shape, size, and location between the targets included in this study were identified and therefore the clinical implications of these differences should be further investigated.
authors.affiliation: Medical Radiation Physics, Stockholm University and Karolinska Institutet, P9 Heliport, 17176, Stockholm, Sweden, helena.sandstrom@ki.se.
authors.forename: Helena
authors.initials: H
authors.lastname: Sandström
authors.forename: Håkan
authors.initials: H
authors.lastname: Nordström
authors.forename: Jonas
authors.initials: J
authors.lastname: Johansson
authors.forename: Per
authors.initials: P
authors.lastname: Kjäll
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Jokura
authors.forename: Iuliana
authors.initials: I
authors.lastname: Toma-Dasu
mesh_terms: D000368:Aged; D001254:Astrocytoma / Q000601:surgery*; D001932:Brain Neoplasms / Q000601:surgery*; D002426:Cavernous Sinus / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008577:Meningeal Neoplasms / Q000601:surgery*; D008579:Meningioma / Q000601:surgery*; D008875:Middle Aged; D015588:Observer Variation; D010818:Practice Patterns, Physicians'; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods*