title: Air kerma strength characterization of a GZP6 Cobalt-60 brachytherapy source.
abstract: BACKGROUND
  Task group number 40 (TG-40) of the American Association of Physicists in Medicine (AAPM) has recommended calibration of any brachytherapy source before its clinical use. GZP6 afterloading brachytherapy unit is a (60)Co high dose rate (HDR) system recently being used in some of the Iranian radiotherapy centers.
  
  
  OBJECTIVE
  In this study air kerma strength (AKS) of (60)Co source number three of this unit was estimated by Monte Carlo simulation and in air measurements.
  
  
  METHODS
  Simulation was performed by employing the MCNP-4C Monte Carlo code. Self-absorption of the source core and its capsule were taken into account when calculating air kerma strength. In-air measurements were performed according to the multiple distance method; where a specially designed jig and a 0.6 cm(3) Farmer type ionization chamber were used for the measurements. Monte Carlo simulation, in air measurement and GZP6 treatment planning results were compared for primary air kerma strength (as for November 8th 2005).
  
  
  RESULTS
  Monte Carlo calculated and in air measured air kerma strength were respectively equal to 17240.01 μGym(2) h(-1) and 16991.83 μGym(2) h(-1). The value provided by the GZP6 treatment planning system (TPS) was "15355 μGym(2) h(-1)".
  
  
  CONCLUSIONS
  The calculated and measured AKS values are in good agreement. Calculated-TPS and measured-TPS AKS values are also in agreement within the uncertainties related to our calculation, measurements and those certified by the GZP6 manufacturer. Considering the uncertainties, the TPS value for AKS is validated by our calculations and measurements, however, it is incorporated with a large uncertainty.
authors.affiliation: Medical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Mohammad Taghi Bahreyni
authors.initials: MT
authors.lastname: Toossi
authors.affiliation: Medical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Ghorbani
authors.affiliation: Physics Department, School of Sciences, Sabzevar Tarbiat Moallem University, Sabzevar, Iran.
authors.forename: Ali Asghar
authors.initials: AA
authors.lastname: Mowlavi
authors.affiliation: Reza Radiotherapy and Oncology Center, Mashhad, Iran.
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Taheri
authors.affiliation: Department of Radiotherapy, Omid University Hospital, Mashhad, Iran.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Layegh
authors.affiliation: Reza Radiotherapy and Oncology Center, Mashhad, Iran.
authors.forename: Yasha
authors.initials: Y
authors.lastname: Makhdoumi
authors.affiliation: Comprehensive Cancer Center of Nevada, 3730 S. Eastern Avenue, Las Vegas, NV, United States.
authors.forename: Ali Soleimani
authors.initials: AS
authors.lastname: Meigooni
keywords: Air kerma strength; GZP6 HDR system; In air measurement; MCNP 4C Monte Carlo code