Monte Carlo dosimetry study of newly designed shielded applicators for intensity modulated brachytherapy of cervical and vaginal cancers.

Introduction: The utilization of metal shields in intensity-modulated brachytherapy (IMBT) enables the modulation of the dose, resulting in improved conformance to the tumor while simultaneously reducing the doses to organs at risk (OARs). Utilizing higher-energy sources like Co in IMBT for cervical and vaginal cancers has consistently posed challenges. This study evaluates the dosimetric aspects of modified applicators designed for IMBT using Co and Ir sources.

Materials And Methods: GATE, a Geant4-based simulation code, was utilized to model and simulate four distinct applicators. The clinical applicators were redesigned to place the structure of the source tube and the shield while keeping the general characteristics unchanged. These shields were evaluated by calculating transmission factors (TFs) and the dose homogeneities were also determined.

Result: Transmission factors for the IMBT technique in redesigned intrauterine applicators and tungsten shields for iridium and cobalt sources were at least 12.8 and 65.4%, and these values were obtained for the intravaginal applicator at 0.2 and 7.0%, respectively. The dose homogeneities for all combinations of radionuclide-shield were within a 15% range of the non-IMBT applicators.

Conclusion: This study has quantitatively evaluated the dosimetric effect of tungsten shields in the IMBT technique for cervical and vaginal cancer using cobalt sources. Ir compared to Co resulted in higher effectiveness for the designed intrauterine and intravaginal shields. while implementing tungsten shields in the redesigned applicators against the Co source may not offer complete protection, it does show promising results in reducing the dose to organs at risk.