**3.1 60Co HDR source**

The 60Co HDR source (model Co0.A86, manufactured by BEBIG) was simulated in this work, and all the comparisons were made for the same source model. It is composed of homogeny cobalt 60 cylindrical core with L = 3.5 mm (length) and 0.5 mm in diameter (density = 8.09 gcm�<sup>3</sup> ). The active core is surrounded by air shell and encapsulated in a stainless steel cylindrical capsule with 0.15 mm thickness and 1 mm for the external diameter. We considered 0.9 mm and 2 mm for the source cable diameter and length, respectively, **Figure 1a**. The activity of the cobalt source used in this work was A0 = 81.56 GBq, and the cobalt 60 half-life is t1/2 = 5.27 years. The density used for the stainless steel is 8.03 gcm�<sup>3</sup> for both the capsule and the source cable [2].
