A novel 3D-printed brachytherapy applicator and Monte Carlo model for the treatment of conjunctival tumors

Purpose: To develop a custom low dose rate brachytherapy applicator for the treatment of conjunctival malignancies which leverages 3D-printing technology to provide enhanced design flexibility and availability.

Methods: An elliptical shell applicator inspired by ocular surgery postoperation conformer shells was developed for the placement of the applicator around the cornea of the eye, with a central hole to provide patient comfort. The applicator featured 2 concentric circles of slots for iodine-125 seeds, providing customization of the dose distribution depending on the location of the target. The applicator was modeled using computer-aided design software. The resultant model STL file was used for 3D printing of the applicator and the development of a Monte Carlo model of the applicator and its dose distribution.

Results: The applicator was successfully 3D printed using biocompatible resin, which could be sterilized for treatment after manual source loading. A Geant4 model of the applicator was created directly from the STL model and was applied to a phantom to estimate the dose distribution delivered by the applicator. The toroidal dose distribution allowed for treatment of the conjunctiva while reducing dose to the cornea compared to traditional eye plaque designs.

Conclusions: A custom 3D-printed applicator was successfully developed and modeled for the treatment of conjunctival malignancies. This novel applicator design potentially provides higher quality, more customizable dose distributions for patients and the simplicity of the design makes it accessible for any clinic with 3D-printing technology.