3D printing of individual skin brachytherapy applicator: design, manufacturing, and early clinical results

Purpose
One of the main challenges in facial region brachytherapy is fixation of vendor-delivered standard applicators. Reproducibility can be maintained; however, there are frequent problems with applicator fitting to the skin surface in pleated regions. Manually prepared individual moulds require technological facilities and highly-trained staff. This article presents 3D-printed applicator preparation for a particular patient skin brachytherapy, using low-cost equipment and free software. We described applicator preparation in a step-by-step workflow.

Material and methods
This study demonstrated preparation of a skin brachytherapy applicator for a challenging recurrent tumor located in the nose bridge. During first visit of patient, fiducial markers were placed to enclose treated region. Patient was computed tomography (CT)-scanned, and reconstruction of target volume and surrounding organs at risk (OARs) were performed using treatment planning system (TPS). In TPS on patient’s surface, a 1-cm thick bolus was added as a body of applicator. Inside the bolus, source paths were designed, and pre-plan was prepared. Using Beben – DICOM to standard triangle language (STL) software, the body of applicator and source-paths from pre-planning was transformed into an STL file, which was used as a solid definition in 3D printing.

Results
The printed applicator fitted very well, and its’ placement was quickly consistent regarding placing and securing. CTV was slightly broader in treatment plan (0.34 cm3 vs. 0.31 cm3), and doses given to CTV were lower, except for V150, which was higher for the realized plan (1.15% vs. 1.83%). All reported doses to OARs were lower in the realized plan.

Conclusions
A low-cost 3D printer and widely available PLA filaments seem feasible to produce individual contact applicators for skin brachytherapy. Beben – DICOM to STL software and presented workflow appear to be convenient and simple tool.