Neutrons absorbed dose rate calculations for interstitial brachytherapy with 252Cf sources

The AAPM TG-43 protocol was used to evaluate the neutron absorbed dose rate from Cf-252 sources for two tissue substitute materials, five normal tissues and six malignant tumours. Three Cf-252 source models (AT, VariSource and mu Selectron) were simulated using the Monte Carlo MCNPX code in spherical geometry for obtaining the following factors: (a) conversion coefficient of neutron air kerma strength, (b) neutron dose rate constant, (c) neutron radial dose function, (d) geometry function, (e) anisotropy function and (f) neutron absorbed dose rate. For the Cf-252 AT source and a Watt fission spectrum, the calculated reference neutron dose rate in water was D-N(r(0), theta(0)) = 1.916cGy h(-1) mu g(-1). The results for the reference neutron dose rate in normal tissues and malignant tumours show how small variations in their elemental composition produce variations in the neutron absorbed dose rate up to 14.9% and 8.4%, respectively, when water and muscle are the reference medium. (C) 2007 Elsevier B.V. All rights reserved.