This study is to evaluate the influence of using different matrix size of smoothing filter for image post-processing and various slice thickness during MR imaging on dose estimation in Ir-192 HDR brachytherapy via normoxic polymer gel dosimeter. Our results show its sensitive nature in gel dosimeter while changing these parameters, among which the combination of 2mm slice thickness of MR images and [5x5] smoothing filter are considered the optimal parameters to provide accurate dose estimations and isodose curves.