Determining the effects of microsphere and surrounding material composition on 90Y dose kernels using egsnrc and mcnp5

Purpose: Recent advances in the imaging of90Y using positron emission tomography (PET) and improved uncertainty in the branching ratio for the internal pair production component of 90Y decay allow for a more accurate determination of the activity distribution of 90Y microspheres within a patient. This improved activity distribution can be convolved with the dose kernel of 90Y to calculate the dose distribution within a patient. This work investigates the effects of microsphere and surrounding material composition on 90Y dose kernels using egsnrc and mcnp5 and compares the results of these two transport codes. Methods: Monte Carlo simulations were performed withegsnrc and mcnp5 to calculate the dose rate at multiple radial distances around various 90Y sources. Point source simulations were completed with mcnp5 to determine the optimal electron transport settings for this work. After determining the optimal settings, point source simulations were completed using egsnrc (user code edknrc) and mcnp5 in water and liver [as defined by the International Commission on Radiation Units and Measurements (ICRU) Report 44]. The results were compared to ICRU Report 72 reference data. Point source simulations were also completed in water with a density of 1.06 g·cm−3 to evaluate the effect of the density of the surrounding material. Glass and resin microsphere simulations were performed with average and maximum diameter and density values (based on values given in the literature) in water and in liver. The results were compared to point source simulation results using the same transport code and in the same surrounding material. All simulations had statistical uncertainties less than 1%. Results: The optimal transport settings inmcnp5 for this work included using the energy-and step-specific algorithm (DBCN 17J 2) and ESTEP set to 10. These settings were used for all subsequent simulations with mcnp5. The point source simulations in water for both egsnrc and mcnp5 were found to agree within 2% of the ICRU 72 reference data over the investigated range. Point source simulations in liver had large differences relative to ICRU 72, approaching −60% near the maximum range of 90Y. These differences are mostly attributed to the difference in density between water (1.0 g·cm−3) and liver (1.06 g·cm−3). Glass and resin microsphere simulations showed a slight decrease in the dose rate near the maximum range of 90Y relative to the point source simulations. The largest relative differ