Advancing iris melanoma brachytherapy: Eye plaque models for Monte Carlo simulations and 3D dosimetric datasets

To develop and benchmark eye plaque models for Monte Carlo (MC) simulation of iris melanoma brachytherapy and to develop a database of 3D dose distributions for the iris plaques containing ${}^{103}\mathrm{Pd}$ , ${}^{125}I$ , and ${}^{131}\mathrm{Cs}$  seeds.

Five iris plaque models are developed with egs_brachy using published dimensions and material data; previously benchmarked seed models are used. Three plaque models are based on those used by the Mayo Clinic, consisting of a modification of the COMS 22 mm plaque design with a 10 mm void in the center surrounded by an inner collimating lip; plaques span ${180}^{\circ }$ , ${270}^{\circ }$ , and ${360}^{\circ }$ arcs. Two additional plaques are modeled: a modified Iris-270 plaque with no collimating lips; a partially-loaded COMS 22 mm plaque with no insert. Plaques are simulated in a water phantom with dose scored in (0.05 ${\mathrm{cm})}^3$ voxels. Simulations under TG-43 conditions are also carried out. Doses are compared to previously published data for validation.

The eye plaque models will be distributed with egs_brachy on GitHub (https://github.com/clrp-code/egs_brachy), along with an input file to facilitate custom simulations. The dosimetric database (https://doi.org/10.5281/zenodo.14776641) is comprised of 3D dose distributions for each plaque type, simulation condition, and radionuclides.

The iris plaque models enable custom simulations with the open-access egs_brachy code. The database of 3D dose distributions supports advanced dose evaluations, as recommended by AAPM Task Group 221 on Ocular Brachytherapy. Overall, this work supports adoption of model-based dose evaluations for brachytherapy as recommended by TG-186.