Toossi MTB et al. / GZP6-TG43 171 FIGURE 1. Schematic diagram illustrating six GZP6 source braids, containing active and nonactive pellets. Each source is allocated to one separate channel. The sources 1-5 are stationary while the source No. 6 is stepper. culations around these implants were performed using the traditional dose calculation technique. However, presently, the Task Group 43 (TG-43) report of American Association of Physicists in Medicine(AAPM) has recommended determina- tion of dosimetric parameters, such as radial dose function, anisotropy function (ANF), etc., of any brachytherapy sourcebefore its clinical use.9 Also according to the AAPM TG-56 such parameters are required as input data and for verification of the treatment planning system.10 The newly designed GZP6 HDR 60Co brachy- therapy unit has been recently employed for the clinical practice in Iran. Unlike the HDR 192Ir sys- tems, which contain one source, the GZP6 unit includes six different sources (Figure 1). Each source is designated to a separate channel in the HDR unit. Five of these six sources are stationary, and the 6th source (i.e. source number 6) has step- ping (dwelling) capability that could be used for FIGURE 2. A schematic view of the GZP6 source braid number 3 illustrating the di- mensions of active cylindrical 60Co and non-active steel pellets as well as TG43U1 coordinate systems. This diagram is schematic and is not to scale. treatment of patients with longer active length. As shown in Figure 1, each source is composed of a source-braid or packing, consist of 1, 2, 3 or 4 ra- dioactive source pellets as well as a number of non active steel pellets. In order to make these source Radiol Oncol 2012; 46(2): 170-178.