title: Anatomic landmarks versus fiducials for volume-staged gamma knife radiosurgery for large arteriovenous malformations.
abstract: OBJECTIVE
  The purpose of this investigation was to compare the accuracy of using internal anatomic landmarks instead of surgically implanted fiducials in the image registration process for volume-staged gamma knife (GK) radiosurgery for large arteriovenous malformations.
  
  
  METHODS
  We studied 9 patients who had undergone 10 staged GK sessions for large arteriovenous malformations. Each patient had fiducials surgically implanted in the outer table of the skull at the first GK treatment. These markers were imaged on orthogonal radiographs, which were scanned into the GK planning system. For the same patients, 8-10 pairs of internal landmarks were retrospectively identified on the three-dimensional time-of-flight magnetic resonance imaging studies that had been obtained for treatment. The coordinate transformation between the stereotactic frame space for subsequent treatment sessions was then determined by point matching, using four surgically embedded fiducials and then using four pairs of internal anatomic landmarks. In both cases, the transformation was ascertained by minimizing the chi-square difference between the actual and the transformed coordinates. Both transformations were then evaluated using the remaining four to six pairs of internal landmarks as the test points.
  
  
  RESULTS
  Averaged over all treatment sessions, the root mean square discrepancy between the coordinates of the transformed and actual test points was 1.2 +/- 0.2 mm using internal landmarks and 1.7 +/- 0.4 mm using the surgically implanted fiducials.
  
  
  CONCLUSIONS
  The results of this study have shown that using internal landmarks to determine the coordinate transformation between subsequent magnetic resonance imaging scans for volume-staged GK arteriovenous malformation treatment sessions is as accurate as using surgically implanted fiducials and avoids an invasive procedure.
authors: Department of Radiation Oncology, University of California, San Francisco, School of Medicine, San Francisco, CA 94143, USA. ppetti@radonc.ucsf.edu
authors: Paula L
authors: PL
authors: Petti
authors: Joy
authors: J
authors: Coleman
authors: Michael
authors: M
authors: McDermott
authors: Vernon
authors: V
authors: Smith
authors: David A
authors: DA
authors: Larson
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D016009:Chi-Square Distribution; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000000981:diagnostic imaging / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D019736:Prostheses and Implants; D011859:Radiography; D016634:Radiosurgery / Q000379:methods*