Background: In this study, a fast dose kernel method (DKM) taking into account an appropriate buildup factor to calculate dose rate distributions around brachytherapy sources was presented. In addition, the dose distribution in various tissue-equivalent materials was investigated using this method. Materials and Methods: To validate the accuracy of the proposed method, the dose rates in water was calculated by dose kernel method and those obtained by Monte Carlo simulation, thermoluminescent dosimetry (TLD) measurements and AAPM Task Group 43 (TG-43) formalism were compared. The validated dose kernel method (DKM) and the MCNP5 code were then applied to evaluate the effect of tissue composition on dose distribution around a Low Dose Rate (LDR) Ir-192 source located in phantoms simulating water, bone and lung tissue. Results: The calculated dose rates were in good agreement with published data for water phantom. Statistical analysis showed that there is no significant difference in terms of dose distribution between the method used in this study and other established methods. Also, the results indicated that the tissue composition affects the dose distribution significantly. Based on the results of this study, the assumption of a homogeneous water phantom in dosimetry of radioactive sources used in brachytherapy may lead to either overestimation of up to 45% or underestimation of up to 19% in bone and lung tissues, respectively. Photon isodose distributions in water, bone and lung were also presented.  Conclusion: Results provides an alternative calculating method for quality assurance purposes using a fast and accurate dose kernel method.