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

The purpose of this study is to find fitted functional forms to the anisotr opy function, F(r, theta), and the radial dose function, g(r), in order to characterize dose-rate distributions around all the high-intensity Ir-192 s ources currently in use. Dosimetry data are at present available as tables for: the microSelectron HDR ("classic" and "new" design models), the PDR so urce, and the VariSource HDR source, expressed in terms of the AAPM Task Gr oup No. 43 recommendations. There is only one paper out which introduces a functional form to fit the anisotropy function, but only for symmetric sour ces with respect to the transverse axis. However, dosimetric data of the HD R and PDR sources mentioned above cannot be reproduced with these functiona l forms. In our study F(r,theta) and g(r) published data are fitted with fu nctional forms in such a way that appropriate limits are reached for both f unctions and the maximum fit error approaches the data uncertainty. The ave rage error is less than 1% in all cases. These functional forms make handli ng data easier within the treatment planning system, avoiding the use of ta bulated data. (C) 2001 American Association of Physicists in Medicine.