title: Using matrix summation method for three dimensional dose calculation in brachytherapy.
abstract: OBJECTIVE
  The purpose of this study is to calculate radiation dose around a brachytherapy source in a water phantom for different seed locations or rotation the sources by the matrix summation method.
  
  
  BACKGROUND
  Monte Carlo based codes like MCNP are widely used for performing radiation transport calculations and dose evaluation in brachytherapy. But for complicated situations, like using more than one source, moving or rotating the source, the routine Monte Carlo method for dose calculation needs a long time running.
  
  
  METHODS
  The MCNPX code has been used to calculate radiation dose around a (192)Ir brachytherapy source and saved in a 3D matrix. Then, we used this matrix to evaluate the absorbed dose in any point due to some sources or a source which shifted or rotated in some places by the matrix summation method.
  
  
  RESULTS
  Three dimensional (3D) dose results and isodose curves were presented for (192)Ir source in a water cube phantom shifted for 10 steps and rotated for 45 and 90° based on the matrix summation method. Also, we applied this method for some arrays of sources.
  
  
  CONCLUSIONS
  The matrix summation method can be used for 3D dose calculations for any brachytherapy source which has moved or rotated. This simple method is very fast compared to routine Monte Carlo based methods. In addition, it can be applied for dose optimization study.
authors.affiliation: Physics Department of Payamnor University of Tehran, Tehran, Iran.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Zibandeh-Gorji
authors.affiliation: Physics Department of Sabsevar Tarbiat Moallem University, Sabzevar, Iran ; TRIL, ICTP, Trieste, Italy.
authors.forename: Ali Asghar
authors.initials: AA
authors.lastname: Mowlavi
authors.affiliation: Physics Department of Payamnor University of Mashhad, Mashhad, Iran.
authors.forename: Saeed
authors.initials: S
authors.lastname: Mohammadi
keywords: 192Ir brachytherapy source; Dose distribution; MCNPX code; Matrix summation method