Dose rate calculations around Ir-192 brachytherapy sources using a Sievertintegration model

The classical Sievert integral method is a valuable tool for dose rate calc ulations around brachytherapy sources, combining simplicity with reasonable computational times. However, its accuracy in predicting dose rate anisotr opy around Ir-192 brachytherapy sources has been repeatedly put into questi on. In this work, we used a primary and scatter separation technique to imp rove an existing modification of the Sievert integral (Williamson's isotrop ic scatter model) that determines dose rate anisotropy around commercially available Ir-192 brachytherapy sources. The proposed Sievert formalism prov ides increased accuracy while maintaining the simplicity and computational time efficiency of the Sievert integral method. To describe transmission wi thin the materials encountered, the formalism makes use of narrow beam atte nuation coefficients which can be directly and easily calculated from the i nitially emitted Ir-192 spectrum. The other numerical parameters required f or its implementation, once calculated with the aid of our home-made Monte Carlo simulation code, can be used for any Ir-192 source design. Calculatio ns of dose rate and anisotropy functions with the proposed Sievert expressi on, around commonly used Ir-192 high dose rate sources and other Ir-192 elo ngated source designs, are in good agreement with corresponding accurate Mo nte Carlo results which have been reported by our group and other authors.