Comparison of dosimetry parameters of two commercially available Iodine brachytherapy seeds using Monte Carlo calculations

Background: Iodine brachytherapy sources with low photon energies have been widely used in treating cancerous tumors. Dosimetric parameters of brachytherapy sources should be determined according to AAPM TG-43U1 recommendations before clinical use. Monte Carlo codes are reliable tools in calculation of these parameters for brachytherapy sources. Materials and Methods: Dosimetric parameters (dose rate constant, radial dose function, and anisotropy function) of two I-125 brachytherapy sources (models LS-1 and Intersource) were calculated with MCNP4C Monte Carlo code following task group #43 (TG-43U1) recommendations of American Assossiation of Physicists in Medicine. The simulations were done inside a spherical water phantom because of its tissue equivalent properties. The Monte Carlo simulations for radial dose function were performed at distances ranging from 0.25 to 10 cm from the source center. The anisotropy functions F(r, θ), for both sources, were calculated at distances of 1, 2, 3, 5 and 7 cm from the source center for angles ranging from 15 to 90 degree. Results: The results of the Monte Carlo simulation indicated a dose rate constant of 0.952 cGyh -1U-1 and 0.986 cGyh -1U-1 for models LS-1 and Intersource, respectively. The tabulated data and fifth order polynomial coefficients for radial dose functions along the source are described in this paper. The results indicated that the anisotropy in dose distribution increased along the source axis. Conclusion: The obtained results were in good agreement with measurements and calculations of other investigators, using other Monte Carlo codes. Iran. J. Radiat. Res., 2010 7 (4): 217-222