title: Functional stereotactic radiosurgery involving a dedicated linear accelerator and gamma unit: a comparison study.
abstract: OBJECTIVE
  The purpose of this work was to investigate the targeting and dosimetric characteristics of a linear accelerator (LINAC) system dedicated for stereotactic radiosurgery compared with those of a commercial gamma knife (GK) unit.
  
  
  METHODS
  A phantom was rigidly affixed within a Leksell stereotactic frame and axial computerized tomography scans were obtained using an appropriate stereotactic localization device. Treatment plans were performed, film was inserted into a recessed area, and the phantom was positioned and treated according to each treatment plan. In the case of the LINAC system, four 140 degrees arcs, spanning +/-60 degrees of couch rotation, were used. In the case of the GK unit, all 201 sources were left unplugged. Radiation was delivered using 3- and 8-mm LINAC collimators and 4- and 8-mm collimators of the GK unit. Targeting ability was investigated independently on the dedicated LINAC by using a primate model. Measured 50% spot widths for multisource, single-shot radiation exceeded nominal values in all cases by 38 to 70% for the GK unit and 11 to 33% for the LINAC system. Measured offsets were indicative of submillimeter targeting precision on both devices. In primate studies, the appearance of an magnetic resonance imaging-enhancing lesion coincided with the intended target.
  
  
  CONCLUSIONS
  Radiosurgery performed using the 3-mm collimator of the dedicated LINAC exhibited characteristics that compared favorably with those of a dedicated GK unit. Overall targeting accuracy in the submillimeter range can be achieved, and dose distributions with sharp falloff can be expected for both devices.
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles School of Medicine, Los Angeles 90095-6951, USA. solberg@radonc.ucla.edu
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Solberg
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Goetsch
authors.forename: Michael T
authors.initials: MT
authors.lastname: Selch
authors.forename: William
authors.initials: W
authors.lastname: Melega
authors.forename: Goran
authors.initials: G
authors.lastname: Lacan
authors.forename: Antonio A F
authors.initials: AA
authors.lastname: DeSalles
mesh_terms: D005373:Film Dosimetry; D006801:Humans; D019047:Phantoms, Imaging; D016634:Radiosurgery / Q000592:standards*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000295:instrumentation / Q000592:standards*; D014057:Tomography, X-Ray Computed