Monte Carlo dosimetry of 60Co HDR brachytherapy sources

Monte Carlo based dosimetry is presented for three 60Co HDR sources with a unique configuration of two active pellets in contact or spaced 9 and 11 mm apart. Results are presented in Cartesian "away and along" as well as polar coordinates following the AAPM TG-43 dosimetric formalism. Iso-dose rate contours around the sources in Cartesian coordinates reveal that significant differences between the three source designs exist only close to the source centers where dose rate distributions bear the effect of the unique source configurations. Dose rate constants of all three sources are accurately described by an equation of the form: lambda(cGyh(-1)U(-1))=lambda*pointG(1 cm,90 degrees) = 1.094*G(1 cm,90 degrees) where lambdapoint is the dose rate constant of a bare 60Co point source and G(1 cm,90 degrees) is the "exact" source geometry factor as defined by the TG-43. Radial dose and anisotropy function data extracted using the point source approximated geometry factors are tabulated for all three source designs. Finally, the dependence and variation of the above TG-43 parameters are discussed and it is demonstrated that the dosimetric properties of high-energy photon emitters are largely dependent on radionuclide source distribution.