Positron range and coincidence non-collinearity in SimSET

The authors have modified SimSET to model positron range and annihilation radiation non-collinearity. Positron range in water is sampled using the empirical model developed by Palmer and Brownell (IEEE Trans. Med. Imag., vol. 11, p. 373-8, 1992). The positron is projected from the decay location in a random direction with adjustment for the density and effective atomic number and weight of intervening tissues. The positron range algorithm was validated by comparing simulated range distributions to the model and with data published by Derenzo (5th Int. Conf. Positron Annihilation, Sendai, Japan, 1979). Annihilation non-collinearity is simulated as a Gaussian-distributed variation from 180 degrees with a standard deviation of 0.5 degrees. Tests verify the simulated noncollinearity is Gaussian distributed and that the azimuthal angle is unbiased