title: A simple and effective method for validation and measurement of collimator output factors for Leksell Gamma Knife Perfexion.
abstract: Accurate determination of collimator output factors is important for Leksell Gamma Knife radiosurgery. The new Leksell Gamma Knife Perfexion system has a completely redesigned collimator system and the collimator output factors are different from the other Leksell Gamma Knife models. In this study, a simple method was developed to validate the collimator output factors specifically for Leksell Gamma Knife Perfexion. The method uses double-shot exposures on a single film to eliminate repeated setups and the necessity to acquire dose calibration curves required for the traditional film exposure method. Using the method, the collimator output factors with respect to the 16 mm collimator were measured to be 0.929 +/- 0.009 and 0.817 +/- 0.012 for the 8 mm and the 4 mm collimator, respectively. These values are in agreement (within 2%) with the default values of 0.924 and 0.805 in the Leksell Gamma Plan treatment planning system. These values also agree with recently published results of 0.917 (8 mm collimator) and 0.818 (4 mm collimator) obtained from the traditional methods. Given the efficiency of the method, measurement and validation of the collimator output factors can be readily adopted in commissioning and quality assurance of a Leksell Gamma Knife Perfexion system.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, CA, USA. lijunma@radonc.ucsf.edu
authors.forename: Lijun
authors.initials: L
authors.lastname: Ma
authors.forename: Per
authors.initials: P
authors.lastname: Kjäll
authors.forename: Josef
authors.initials: J
authors.lastname: Novotny
authors.forename: Håkan
authors.initials: H
authors.lastname: Nordström
authors.forename: Jonas
authors.initials: J
authors.lastname: Johansson
authors.forename: Lynn
authors.initials: L
authors.lastname: Verhey
mesh_terms: D000465:Algorithms; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D016634:Radiosurgery / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity