Investigation of the effect on the dose distribution of the effective atomic number of brachytherapy capsule

Brachytherapy, which is a special case of radiotherapy method in cancer treatment, is practiced by locating an encapsulated radionuclide source into or vicinity of a tumor. In this thesis, the capsule material of the radionuclide source has been changed with the elements mixtures, in which the effective atomic numbers are regularly increased. Then hypothetic sources have been designed by using these hypothetic mixtures, which prepared carefully according to acceptability of tissue and the properties of the elements. To calculate the preferred effective atomic number, an algorithm, which gives the rates of the elements in the mixtures, was developed with the help of Brute Force method. EGSnrcMP GUI Monte Carlo (MC) simulation program for all effective atomic numbers were used to individually calculate the cross sections in the ICRU standards. Later, the dose distributions were calculated in a water phantom with the help of the iode spectrum by using EGSnrc simulation codefor the effective atomic numbers of each mixture. During the simulation, Amersham Health Model 6711 125I LDR brachytherapy source has been used without changing its geometric design and radionuclide content. Eventually, the dosimetric parameters have been calculated using the dose rates obtained by Monte Carlo simulation. These calculated dosimetric parameters for 125I Model 6711 source have been compared with those of the source with original capsule, which also calculated by Monte Carlo simulation. In addition, a large effective atomic number scale was obtained for the capsule material of the source for the future studies. Keywords: Brachytherapy, Effective Atomic Number, Monte Carlo Simulation