Encapsulated source contact dose estimates incorporating secondary electron emission

Abstract

Secondary electron emission generated at the surface of thin material from interaction with gamma rays form a significant component of the surface dose. The intensity of this emission is known to vary with material composition and incident radiation energies. The goal of this research effort is to estimate the emission strength from radioactive sources utilized in the early history of cancer Brachytherapy, and develop dose conversion factors from that data. Data was obtained by utilizing a comparative stochastic analysis, conducted with the Monte Carlo radiation transport code MCNPX. Emission intensities were measured at the surface of source encapsulation and at increasing distances in tissue equivalent material. It is shown that the results obtained correlate to the historical trends, however the electron component of the simulated emission is of greater by several orders of magnitude than that previously estimated. The dose conversion factors found from simulation will assign a higher absorbed dose than those currently published. The corollary is that the current published values are under attributing dose for a given radiation injury, which hinders effective treatment.