3142 - 3D-Printed Seed Placement Template for ¹²⁵I Seed Plaque Assembly with Custom Eye Plaques

K. G. Calabresi¹, J. Emrich^2,3, S. Belko⁴, M. Daley⁵, R. Pugliese⁵, and F. Mourtada²; ¹LSU Health Sciences Center New Orleans, School of Medicine, New Orleans, LA, ²Department of Radiation Oncology, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, PA, ³Wills Eye Hospital, Philadelphia, PA, ⁴Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, PA, ⁵Thomas Jefferson University, Health Design Lab, Philadelphia, PA

Purpose/Objective(s): Brachytherapy for ocular melanomas and retinoblastomas involves the temporary placement of low-dose rate seeds arranged on eye plaques. At one institution, ¹²⁵I seed sources are placed in custom arrangements on gold plaques to optimally target the tumor volume. In the existing procedure for plaque construction, the medical physicist glues seeds onto the plaque while visually following a printout of a simulated plaque from the treatment plan. The seed placement accuracy can be subjective and user-dependent, so the existing method may result in undue risk of seed placement error. Here we explored using a 3D printed template to improve the accuracy of seed placement on model plaques, hypothesizing that use of the template would decrease seed arrangement discrepancies between the treatment plan and the actual assembled plaque. Materials/

Methods: Model plaques were 3D printed (Formlabs Clear Resin) and painted gold to mimic clinical plaques used in brachytherapy. Seed placement templates were designed by adding seed cutouts corresponding to seed locations from clinical plans (Eye Physics Plaque Simulator), then printed in Formlabs Elastic 50A resin. Once cured, the flexible template was placed on top of the model plaque, and an ultra-fine pen was used to mark locations for the seed placements. The template was then removed. Non-radioactive ¹²⁵I seeds were glued onto the model plaques following the seed pattern from clinically relevant treatment plans (six 15-mm round and six 22-mm notched plaques) with and without use of a template. The constructed plaques were photographed using a DSLR camera with micro lens mounted on a vertical stand. Images were processed in a photo editing application. An image analysis program developed in a programming environment was used to assess the accuracy of seed placement compared to the treatment plan. A two-sample t-test was used for statistical analyses.
Results: The average seed displacement of the non-templated and templated plaques respectively were 1.53 mm (SD = 0.62) and 0.70 mm (SD = 0.31). The average seed orientation difference of the non-templated and templated plaques compared to the treatment plan were 6.10 degrees (SD = 5.36) and 3.75 degrees (SD = 3.13). Both seed displacement (p < 0.001) and orientation difference (p = 0.008) were significantly lower with use of the template to guide seed placement compared to seed placement without the template.
Conclusion: A template to guide seed placement is a novel tool for building custom plaques. Because the template is 3D-printed for each plaque, it can be made to fit any plaque size and to display a custom seed arrangement. Use of the template may reduce the risk of extreme discrepancies in seed placement clinically and reduce physicist exposure to radiation if it decreases the time spent building plaques. In future work, we plan to test the function of the template with clinical plaques to verify the tool’s practical utility.