SU-FF-T-17: Impact of Applicator and Dummy Pellets On the TG 43 Parameters of Selectron Cs-137 Source

Abstract

Introduction In this study, dose rate distribution around a spherical pellet source, from a low dose rate (LDR) Selectron remote afterloading system, have been determined using Experimental and Monte Carlo Simulation techniques. Materials and Methods: Monte Carlo simulations were performed using MCNP4C code, for a single pellet source in water medium and Plexiglas and measurements were performed in Plexiglas phantom material using LiF TLD chips. Absolute dose rate distribution and the TG-43 dosimetric parameters such as dose rate constant, radial dose functions and anisotropy functions were obtained for a single pellet source. In order to investigate the effect of the applicator, and surrounding pellets on dosimetric parameters of the source, the simulations were repeated for 6 different arrangements with a single active source and five non-active pellets inside central metallic tubing of a vaginal cylindrical applicator. In commercial treatment planning systems (TPS) the attenuation effects of the applicator and inactive spacers on total dose are neglected. Results The results indicate that this effect could lead to overestimation of the calculated anisotropy function by up to 7% along the longitudinal axis of the applicator especially beyond the applicator tip. The radial dose function and anisotropy function of the new source design have been tabulated for each configuration. Conclusions Impact of the Applicator and Dummy Pellets on the TG-43 Parameters of Selectron Cs-137 Source has been determined using TLD and Monte Carlo calculations. The results indicate neglecting the applicator and dummy pellets could cause significant errors in F(r, θ).