Monte Carlo calculation of energy build-up factors in the range from 15 keV to 100 keV, with special reference to the dosimetry of125I seeds

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Abstract
Dose build-up factors of point isotropic gamma sources in water have been calculated based on the formalism given by M Berger and using the Monte Carlo code EGS4. All effects of penetration, especially electron transport and Rayleigh scattering have been included. Moreover more up-to-date values of attenuation and energy-absorption coefficients were used. It was found that the new build-up factors show considerable deviations relative to Berger's. Finally the behaviour of build-up factors in finite, spherically shaped media was investigated. Results were applied to the dose distribution of 125I seeds. Accordingly, the special 125I seed energies for two different models were treated separately.