3D-printed radiopaque episcleral plaques with radioactive collimating cavities for enhanced dose delivery in brachytherapy.

Abstract

Purpose: Episcleral plaque brachytherapy (EPBT) is a well-established treatment. However, the lateral dose to healthy tissues, such as the sclera, retina, and optic nerve is often problematic and results in side effects. This study proposes an innovative approach based on the 3D-printing of radiopaque polymer plaques featuring cylindrical radioactive cavities (CRC) with a potential collimating effect on radiation delivery to tumors.

Methods and materials: A CAD model based on the COMS protocol was created and 3D-printed using radiopaque PEEK polymer. Cylindrical cavities (1 mm depth/diameter) were evenly spaced on the plaque's inner surface. Two radioactive layouts (RL₁: uniform loading; RL₂: radial gradient loading) were designed. µCT imaging was used to assess the geometric accuracy of the 3D-printed CRC EPs, and dose distribution was evaluated for the two (2) radioactive layouts using MAGIC-pf gel dosimetry and T₂-weighted MRI. The resulting dose profiles were compared with those generated by both COMS and SEP plaques.

Results: Radiopaque CRC EPs showed higher central axis dose deposition while minimizing lateral overexposure compared to COMS and SEP plaques, while also providing robust back-shielding. Dose profiles from RL₁ CRC EPs (uniform layout) extended deeper into the eye, whereas RL₂ CRC EPs (with gradient) exhibited a more rapid dose fall-off, producing a concentrated, spherical dose distribution.

Conclusions: 3D-printed radiopaque EPs with radioactivity encapsulated in cylindrical cavities demonstrated the ability to achieve more forward-projected dose profiles in EPBT. This fabrication design and a modulated radioactivity distribution across the EP surface would enable more precise and deeper dose delivery while reducing radiation exposure to lateral healthy tissues.