Aim: To design and study the physical and radiological properties of Heterogeneous Thorax Phantom (HTP).Materials and Methods: The Computed Tomography (CT) images of thorax were imported on treatment planning system and analyzed for measuring the density of chest wall tissue, lung and soft tissue behind the lung. The mean and standard deviation of these different densities were noted and analyzed. A HTP with similar density distribution was made using slabs of SP34 and pinewood. A plan was made on actual patient’s CT  scan and on  HTP by putting 6 MV photon beam of 10x10 cm2 field size and source to surface distance of 100 cms perpendicular to the chest wall using anisotropic analytical algorithm with grid size 0.25 cm. Depths for isodose were measured in both the mediums. The CT scan of HTP was taken at three different interface regions. The doses were planned and  measured at these three interface regions using ionization chamber. Measured and planned doses were compared and analyzed. Results: The mean density of the chest wall, lung and soft tissue were found to be 0.94, 0.28 and 0.98 gm/cc respectively on patient’s CT scan, while 0.99, 0.27 and 0.99 gm/cc respectively in HTP. Variation in planned dose and measured dose on HTP at 6 cm, 10 cm and 18 cm depths were found to be 0.47%, 0.81% and 2.4%. Conclusion: Phantom mimicking thorax site along with advanced third generation Monte Carlo based algorithms which are based on biological dose calculation should be used for more accurate dose calculation.

Keywords: Heterogeneous Phantom; Slab-Pinewood-Slab Phantom; Third Generation Algorithm, Monte Carlo, Across XB; Monaco.