Dose distribution in a cervix phantom quality-assurance using two computer modeling approaches

This study compares two geometric modeling approaches for the computational representation of the three-dimensional Angelika phantom, which is a quality-assurance phantom developed for gynecological brachytherapy applications. A Surface Mesh model and a Macrobodies model were implemented in MCNP6.2 to calculate absorbed dose distributions in Gafchromic EBT3 films irradiated by a¹⁹²Ir HDR source positioned at different locations along the phantom axis. Both approaches reproduced similar angular and longitudinal dose distribution patterns. Higher absorbed dose rates were observed at 45° and 225°, while lower values were found in the phantom plug region due to increased PMMA attenuation. The Surface Mesh model systematically yielded higher absorbed dose rates than the Macrobodies model, with an average difference of approximately 4% and a maximum local difference of 27%. Relative errors associated with the Monte Carlo simulations remained below 1.6% in all scenarios. These results demonstrate that geometric representation influences dose estimates even in homogeneous phantoms. Both approaches proved suitable for quality-assurance applications. However, the Surface Mesh model provided greater geometric fidelity and a closer representation of the original phantom geometry, making it a valuable tool for Monte Carlo benchmarking studies in brachytherapy.