Development on Monte Carlo methodology with scatter correction factor of afterloading 192Ir source

Abstract

Objective To facilitate activity measurement by using the thimble ionization chamber in hospitals, to obtain air kerma scatter correction factor of medical afterloading of 192Ir source by developing an available and convenient calculation method. Methods According to International Atomic Energy Agency （IAEA） 1079 Report to calculate the scatter correction factor of 192ir source, to measure air kerma of 192Ir source with and without lead shield using thimble ionization chamber. Simulation measurement conditions were used to calculate scatter correction factor of 192Ir source and comparison was made between experimental results and literature records. At the same time, the different ionization chamber models were simulated at different room sizes to obtain scattering correction factor of 192Ir source. Results Comparison was made between the simulation scatter correction factors of 192Ir source and experiment by the shadow shield, and the relative deviation was 0.8%. The deviation of the 192Ir activity calculated according to the simulated scatter correction factor and measured by well type ionization chamber was 2.4%. By comparison between the calculated results by using two kinds of spherical ionization chamber and those ones deduced by IAEA 1079 Report, the relative deviations ranged within 0. 3%- 0.4%. Five different types of thimble ionization chamber and different room sizes were simulated and calculated by MC simulation, with the relative deviation within3%. Conclusions Monte Carlo simulation method for calculating afterloading 192ir source＇s scatter correction factor is feasible, and this method is convenient for use in the thimble chamber for brachytherapy QA work in the hospital. Key words: Monte Carlo method; 192Ir source; Scatter correction factor; Thimble ionization chamber