Speaker
Description
Gynecological intracavitary brachytherapy is a standard treatment for cervical and endometrial malignancies. During applicator insertion, such as vaginal cylinders, air gaps often form between the applicator and vaginal mucosa [1]. These heterogeneities introduce uncertainties based on size and location, potentially altering dosimetric distribution [2]. Since commercial Treatment Planning Systems (TPS) assume a homogeneous water-equivalent medium and neglect these perturbations [3], Monte Carlo simulations provide a rigorous method to evaluate dose variations caused by air gaps. To investigate this effect, air gaps were initially modeled using Blender software [4] and incorporated into a female anthropomorphic mesh-type phantom described in ICRP Publication 145 [5], exported in DICOM format. Subsequently, Monte Carlo simulations were performed using the Tool for Particle Simulation (TOPAS) code [6], considering high-dose-rate (HDR) brachytherapy with an $^\mathrm{192}$Ir source. Simulations revealed depth-dose variations between scenarios with and without air gaps, depending heavily on gap size and position. Notably, adjacent tissues showed dose reductions, attributed to geometric displacement and decreased photon interaction in air. This suggests a potential impact on treatment of dose-volume histograms (DVHs). Overall, the results indicated that the presence of air gaps in gynecological intracavitary brachytherapy may lead to clinically relevant alterations in dose distribution, especially as a function of gap size. In this context, Monte Carlo simulation using TOPAS proved to be an effective tool for assessing such heterogeneities, while also highlighting the limitations of conventional homogeneous medium-based planning.
[1] Cameron et al 2008 Brachytherapy 7 355–358
[2] Maxwell et al 2016 Brachytherapy 15 832–838
[3] Srinivas et al 2023 Asian Pac J Cancer Prev 24 1659–1666
[4] Blender Foundation 2018 Blender
[5] ICRP 2020 Ann ICRP 49 13–201
[6] Faddegon et al 2020 Phys Med 72 114–121