title: [Stereotaxic convergent irradiation with the gamma knife. A study of the possibilities for optimizing the dosage distribution].
abstract: OBJECTIVE
  On April 1992, the first stereotactic radiosurgical procedure using the gamma knife was performed at the University Medical School Graz, Department of Neurosurgery. Accurate dose optimization is the foundation of a convenient and responsible utilization of this modality. But there are limits, because the final collimation is only achieved by 1 of the 4 special helm collimators.
  
  
  METHODS
  The possibilities of dose optimization and its influence on the dose distributions were investigated and partly compared with results of film densitometry measurements. In detail, the technique, which uses the same isocenter, but different sized collimators was studied. The influence of these optimization techniques on the resulting dose distributions and the dose gradient at the edge of the treatment planning volume was analyzed. Also the visions for an effective dose optimization are discussed.
  
  
  RESULTS
  With 2 shots of different diameters, located at the same target coordinates and different weighting of time any collimator size between the 4 mm and 18 mm can be achieved. Because of that, a combination of more than 2 collimators is not meaningful. With the combined shots the dose fall gradient was less than that of either of the single shots involved in the combination.
  
  
  CONCLUSIONS
  With the available physical and technical possibilities only a limited, very time consuming optimization is practicable. The quality control of isodose distributions requires optimizations in hard- and software, that enable CT- or MRT-based 3-dimensional visualization and dose volume analysis.
authors.affiliation: Universitätsklinik für Radiologie, Klinische Abteilung für Strahlentherapie, Graz.
authors.forename: G
authors.initials: G
authors.lastname: Stücklschweiger
mesh_terms: D001932:Brain Neoplasms / Q000601:surgery; D006801:Humans; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods / Q000706:statistics & numerical data
vernacular_title: Stereotaktische Konvergenzbestrahlung mit dem Gamma-Knife. Eine Untersuchung der Möglichkeiten zur Optimierung der Dosisverteilung.