ESTRO 2024 - Abstract Book

S368

Beachytherapy - Physics

ESTRO 2024

performed using the TOol for PArticle Simulation (TOPAS) Brachy Monte Carlo (MC) code. 3,4 Different geometries reproducing either single radioactive cavities (RC) lined with 125 I, or conventional commercial 125 I seeds, as well as geometrical patterns of RC or seeds so as to reproduce the conventional protocol of 18-mm COMS plaques (Figure1C,D). The results were scored in a water phantom (illustrated in Figure 1E), which allowed to derive relative dose profiles for each one of the set-ups. Then, the capacity to generate RC distribution profiles optimized to the geometry of uveal melanoma tumors usually difficult to treat (e.g. a tumor extending deep inside of the eye), was explored by using the anatomic geometries derived from clinical cases (Figure 1F). Then, EPs were 3D printed according to a proprietary and original methodology and procedure making use of radiolucent PEEK (polyetheretherketone) as a biocompatible, rigid, and sterilization procedure-resistant material. RC were machined with precision in these plaques, 125 I was added as a liner at the bottom of each well, and cavisites were sealed. An experimental assessment of dose profiles was performed by 3D gel dosimetry (methacrylic-acid gel specifically optimized in our lab for low-dose rate brachytherapy and relatively long exposure times; < 48h). Gels were exposed to loaded CRC plaques, and the profiles were compared with that obtained by MC simulations. MC simulations revealed higher dose deposition rates along the central axis of CRC plaques, compared to the profiles generated by conventional COMS plaques (Figure 1E). The relative dose profiles of CRC plaques appeared projected forward, and not flared on either side of the plate, a phenomenon usually observed for COMS plaques. The results from the MC simulations reveal that RC cavities prevent overexposure of the lateral healthy tissues such as sclera and optic nerve. The concept of RC planning was further explored by modulating the number of RC and relative 125 I activity deposited per RC and per plaque, which allowed to demonstrate the possibility of closely matching profiles with the contours of clinically relevant cases of melanoma tumors extending deep into the eye (Figure 1F). Finally, the 3D printed plaques fabricated with PEEK (Figure 1I), loaded with 125 I and assessed with dosimetric hydrogels, confirmed the lower dose exposure of lateral tissues, as well as the extension of the dose profiles along the central axis of the plaques. Results: