Monte Carlo dosimetry of 60Co HDR brachytherapy sources

Monte Carlo based dosimetry is presented for three Co-60 HDR sources with a unique configuration of two active pellets in contact or, spaced 9 and I I 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(cGy h(-1) U-1)=Lambda(point)*G(1 cm,90degrees) 1.094*G(1 cm,90degrees) where Lambda(point) is the dose rate constant of a bare Co-60 point source and G(1 cm,90degrees) 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. (C) 2003 American Association of Physicists in Medicine.