Investigation of Tissue Heterogeneities Effect on Dose Distribution from 192-Ir Source During Brachytherapy Treatments

Document Type : Original Article


1 Department of Medical Physics, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.

2 Department of Medical Physics, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran

3 Department of Oral and Maxillofacial Radiology, Faculty of Density, Ahvaz Jundishapur University of Medical Sciences, Ahwaz, Iran


Background and objective: The possible defect of recommended protocol by the American Association of Physicists in Medicine (AAPM, TG43) for dosimetry in the field of brachytherapy is that this protocol does not consider tissue heterogeneities (such as bone, lung, …) when applying resulted dosimetry parameters in treatment planning systems. The purpose of this study was to evaluate dose differences with and without heterogeneities in brachytherapy with iridium source (Ir -192)
Subjects and Methods: Dose distribution from microselectron HDR Ir-192 source located in center of the homogeneous water phantom calculated by MCNP-4C simulation method. In different simulations, heterogeneities of bone, lung, air and soft tissue were considered. The effect of source positioning in phantom and distance between source and heterogeneities on dose distribution were evaluated.
Results: The calculated dose, due to heterogeneity of bone, was reduced, while those due to air and lung were increased? Heterogeneity of soft tissues has no meaningful effect on the dose distribution.  Increasing distance from center of phantom decreases dose due to decrease of scattering.
Conclusion: Heterogeneities of bone, lung, and air especially in the near distance from Ir-192 source implanted position can change the dose compared to the water homogeneity phantom. In future Treatment Planning System (TPS) TPS, for accurate dose estimation, the effect of heterogeneities on dose distribution should be considered. Furthermore, in order to acquire the exact dose, due considerations of correct amount of scattering, dosimetry must be carried out on a large enough phantoms.


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