title: An Analytical Method to Calculate Phantom Scatter Factor for Photon Beam Accelerators.
abstract: BACKGROUND
  One of the important input factors in the commissioning of the radiotherapy treatment planning systems is the phantom scatter factor (Sp) which requires the same collimator opening for all radiation fields. In this study, we have proposed an analytical method to overcome this issue.
  
  
  METHODS
  The measurements were performed using Siemens Primus Plus with photon energy 6 MV for field sizes from 5×5cm2to 40×40cm2. Phantom scatter factor was measured through the division of total scatter output factors (Scp), and collimator scatter factor (Sc).
  
  
  RESULTS
  The mean percent difference between the measured and calculated Sp was 1.00% and -3.11% for 5×5, 40×40 cm2field size respectively.
  
  
  CONCLUSIONS
  This method is applicable especially for small fields used in IMRT which, measuring collimator scatter factor is not reliable due to the lateral electron disequilibrium.
authors.affiliation: Ph.D. of Medical Physics, Professor, Department of Medical Physics and Radiation Therapy and Medical Physics Department, Golestan Hospital, Jundishapur University of Medical Sciences, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences: Ahvaz, Iran.
authors.forename: Mohammad Javad Tahmasebi
authors.initials: MJ
authors.lastname: Birgani
authors.affiliation: Ph.D. of Medical Physics, Assistant Professor, Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences: Ahvaz, Iran.
authors.forename: Nahid
authors.initials: N
authors.lastname: Chegeni
authors.affiliation: Ph.D. of Bio Physics, Professor, Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences: Ahvaz, Iran.
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Behrooz
authors.affiliation: M.Sc. of Medical Physics, Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences: Ahvaz, Iran.
authors.forename: Marziyeh
authors.initials: M
authors.lastname: Bagheri
authors.affiliation: Ph.D. of Medical Physics, Assistant Professor, Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences: Ahvaz, Iran.
authors.forename: Amir
authors.initials: A
authors.lastname: Danyaei
authors.affiliation: M.Sc. of Medical Physics, Radiation Therapy and Medical Physics Department, Golestan Hospital, Jundishapur University of Medical Sciences.
authors.forename: Azin
authors.initials: A
authors.lastname: Shamsi
keywords: Phantom scatter factor; Radiotherapy; Total scatter factor