title: Dosimetry and evaluating the effect of treatment parameters on the leakage of multi leaf collimators in ONCOR linear accelerators.
abstract: BACKGROUND
  One of the standard equipment in medical linear accelerators is multi-leaf collimators (MLCs); which is used as a replacement for lead shielding. MLC's advantages are a reduction of the treatment time, the simplicity of treatment, and better dose distribution. The main disadvantage of MLC is the radiation leakages from the edges and between the leaves. The purpose of this study was to determine the effect of various treatment parameters in the magnitude of MLC leakage in linear accelerators.
  
  
  METHODS
  This project was performed with ONCOR Siemens linear accelerators. The amount of radiation leakage was determined by film dosimetry method. The films were Kodak-extended dose range-2, and the beams were 6 MV and 18 MV photons. In another part of the experiment, the fluctuation of the leakage was measured at various depths and fields.
  
  
  RESULTS
  The amount of leakage was generally up to 1.5 ± 0.2% for both energies. The results showed that the level of the leakage and the amount of dose fluctuation depends on the field size and depth of measurement. The amount of the leakage fluctuations in all energies was decreased with increasing of field size. The variation of the leakage versus field size was similar to the inverse of scattering collimator factor.
  
  
  CONCLUSIONS
  The amount of leakage was more for 18 MV compare to 6 MV The percentage of the leakage for both energies is less than the 5% value which is recommended by protocols. The fluctuation of the MLC leakage reduced by increasing the field size and depth.
authors.affiliation: Department of Medical Physics and Medical Engineering, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Keyvan
authors.initials: K
authors.lastname: Jabbari
authors.affiliation: Department of Medical Physics and Medical Engineering, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Muhaddeseh
authors.initials: M
authors.lastname: Akbari
authors.affiliation: Department of Medical Physics and Medical Engineering, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Mohamad Bagher
authors.initials: MB
authors.lastname: Tavakoli
authors.affiliation: Department of Radiation Oncology, Isfahan Milad Hospital, Isfahan, Iran.
authors.forename: Alireza
authors.initials: A
authors.lastname: Amouheidari
keywords: Dosimetry; multi-leaf collimators leakage and film dosimetry; radiation therapy