Comparative study of simulation and experiment in determining 192Ir source strength for brachytherapy quality assurance

This research is of paramount importance as it combines experimental measurements and Monte Carlo simulation to determine the air kerma strength of the 192Ir source, which plays a crucial role in dose calculations for brachytherapy treatment planning. The air kerma strength represents the source strength value, directly influencing the accuracy of dose calculations in cancer treatments. Verifying the source strength during each source exchange is essential to the quality assurance process. In this study, the 192Ir Gammamed Plus source, provided by Varian, was used to calculate the air kerma strength through experimental measurements and Monte Carlo simulation. The measurements were conducted on a brachytherapy system with an HDR 1000 Plus well-type ionization chamber and source tube 70010 from Standard Imaging. Using the MCNP6 code, we constructed a model equivalent to the experimental system, consisting of the source geometry, source tube, and well-type chamber, with source self-absorption also considered. The air kerma strength measurements differed from the certified value by less than 2 %, within the allowable range according to the AAPM TG40 recommendations. The experimental and simulation methods showed strong agreement, with less than 4.1 % discrepancies. Considering source self-absorption, the air kerma strength calculation for the 192Ir source was consistent across both methods. The findings of this study validate that we successfully built an experimental system model using the Monte Carlo simulation with the MCNP6 code. This model can be further developed for future research.