Fitted dosimetric parameters of high dose-rate 192Ir sources according to the AAPM TG43 formalism

The purpose of this study is to find fitted functional forms to the anisotropy function, F(r, theta), and the radial dose function, g(r), in order to characterize dose-rate distributions around all the high-intensity 192Ir sources currently in use. Dosimetry data are at present available as tables for: the microSelectron HDR ("classic" and "new" design models), the PDR source, and the VariSource HDR source, expressed in terms of the AAPM Task Group No. 43 recommendations. There is only one paper out which introduces a functional form to fit the anisotropy function, but only for symmetric sources with respect to the transverse axis. However, dosimetric data of the HDR and PDR sources mentioned above cannot be reproduced with these functional forms. In our study F(r,theta) and g(r) published data are fitted with functional forms in such a way that appropriate limits are reached for both functions and the maximum fit error approaches the data uncertainty. The average fit error is less than 1% in all cases. These functional forms make handling data easier within the treatment planning system, avoiding the use of tabulated data.