Cylindrical silicone applicator for superficial brachytherapy of the finger: Design and manufacturing

To design and fabricate a cylindrical silicone applicator for high-dose-rate (HDR) superficial brachytherapy of the fingers, aiming at improving dose coverage, anatomical conformity, and inter-session reproducibility. This device was intended to offer a practical alternative to the limitations of existing commercial applicators.

A solid, assemblable negative mold was designed using 3D printing technology. This mold enabled shaping of the final applicator by casting of pre-mixed and degassed room temperature vulcanized (RTV) silicone. Design featured a central cavity, a 93.5° open segment to facilitate anatomical adaptation, and nine equidistant holes for catheter insertions. Applicator's performance was evaluated on hand phantom, considering efficacy, flexibility, and mechanical stability. Dosimetric planning was based on CT investigations, in which a subcutaneous treatment volume was simulated. Each catheter included eight dwell positions, and dwell times were modulated to optimize dose distribution and spatial conformity.

The applicator exhibited good flexibility, structural integrity, and appropriate adaptation to different finger morphologies. Catheters remained securely positioned during testing, with no displacements observed. The 100% iso-dose line fully encompassed the target volume, and the maximum surface dose reached 129% of the prescribed dose. Most of 120% isodose was confined within the applicator material, indicating an adequate bolus effect. Dwell time modulation contributed to a uniform dose distribution, especially in peripheral and distal regions of the target volume.

The developed applicator represents an effective, accessible, and reproducible solution for the delivery of HDR brachytherapy in superficial finger lesions, supporting its implementation in clinical settings with limited resources.