Dosimetric characterizations of GZP6 (60)Co high dose rate brachytherapy sources: application of superimposition method

BACKGROUND: Dosimetric characteristics of a high dose rate (HDR) GZP6 Co-60 brachytherapy source have been evaluated following American Association of Physicists in MedicineTask Group 43U1 (AAPM TG-43U1) recommendations for their clinical applications. MATERIALS AND METHODS: MCNP-4C and MCNPX Monte Carlo codes were utilized to calculate dose rate constant, two dimensional (2D) dose distribution, radial dose function and 2D anisotropy function of the source. These parameters of this source are compared with the available data for Ralstron (60)Co and microSelectron(192)Ir sources. Besides, a superimposition method was developed to extend the obtained results for the GZP6 source No. 3 to other GZP6 sources. RESULTS: The simulated value for dose rate constant for GZP6 source was 1.104±0.03 cGyh-1U-1. The graphical and tabulated radial dose function and 2D anisotropy function of this source are presented here. The results of these investigations show that the dosimetric parameters of GZP6 source are comparable to those for the Ralstron source. While dose rate constant for the two (60)Co sources are similar to that for the microSelectron(192)Ir source, there are differences between radial dose function and anisotropy functions. Radial dose function of the (192)Ir source is less steep than both (60)Co source models. In addition, the (60)Co sources are showing more isotropic dose distribution than the (192)Ir source. CONCLUSIONS: The superimposition method is applicable to produce dose distributions for other source arrangements from the dose distribution of a single source. The calculated dosimetric quantities of this new source can be introduced as input data to the GZP6 treatment planning system (TPS) and to validate the performance of the TPS.