Investigation of the Effects of Tissue Inhomogeneities on the Dosimetric Parameters of a Cs-137 Brachytherapy Source using the MCNP4C Code

Document Type : Original Paper

Authors

1 PhD Student of Nuclear Engineering, Faculty of Mechanical Engineering, Shiraz University, Shiraz, Iran.

2 Assistant professor of Nuclear Engineering Dept., , Radiation Research Center, Faculty of Mechanical Engineering, Shiraz University, Shiraz, Iran

3 MSc Student of Nuclear Engineering, Faculty of Mechanical Engineering, Shiraz University, Shiraz, Iran.

Abstract

Introduction: Brachytherapy is the use of small encapsulated radioactive sources in close vicinity of tumors. Various methods are used to obtain the dose distribution around brachytherapy sources. TG-43 is a dosimetry protocol proposed by the AAPM for determining dose distributions around brachytherapy sources. The goal of this study is to update this protocol for presence of bone and air inhomogenities. 
Material and Methods: To update the dose rate constant parameter of the TG-43 formalism, the MCNP4C simulations were performed in phantoms composed of water-bone and water-air combinations. The values of dose at different distances from the source in both homogeneous and inhomogeneous phantoms were estimated in spherical tally cells of 0.5 mm radius using the F6 tally.
Results: The percentages of dose reductions in presence of air and bone inhomogenities for the Cs-137 source were found to be 4% and 10%, respectively. Therefore, the updated dose rate constant (Λ) will also decrease by the same percentages.  
Discussion and Conclusion: It can be easily concluded that such dose variations are more noticeable when using lower energy sources such as Pd-103 or I-125.  

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Iranian Journal of Medical Physics
Volume 7, Issue 3 - Serial Number 3
September and October 2010
Pages 15-20

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History

  • Receive Date: 09 April 2010
  • Revise Date: 18 July 2010
  • Accept Date: 18 August 2010

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