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A Novel Ophthalmic Applicator Design for Brachytherapy for Conjunctival Melanoma


C Lee

C Lee*, H Demirci, J Hayman, University of Michigan, ANN ARBOR, MI

SU-E-T-355 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To design and construct a novel ophthalmic brachytherapy applicator for the treatment of conjunctival melanoma using I-125 radioactive seed sources to overcome the dosimetric limitations of the commonly used standard Collaborative Ocular Melanoma Study (COMS) plaques.

Methods:A commercially available polymethylmethacrylate conformer (Gulden Ophtalmics, Elkins Park, PA) was employed to hold a total of 12 low dose I-125 seeds (model IAI-125A, IsoAid, LLC, Port Richey, FL) distributed along the periphery of the conformer. Three dimensional dose distribution was calculated using the Plaque Simulator software (EyePhysics, LLC, Los Alamitos, CA) to optimize seed distribution pattern. The AAPM TG-43 dose calculation formulism was utilized within the software.

Results:The seed distribution pattern was designed in a way that dose would be delivered to the conjunctival tissue ,while limiting the dose to the cornea and lens. Once the design was finalized, each slot for the seed was fabricated using a 6-axis computer numerical control (CNC) machine available at our institution. The slots were milled into the convex side of the conformer to minimize any patient discomfort and to protect the cornea from direct contact with the seeds.

Conclusion:The difficulty of treating conjunctival melanomas with COMS eyeplaques due to its unique anatomical distribution called for a custom design brachytherapy applicator. The applicator designed in the current study can effectively deliver radiation dose to affected area while minimizing the dose to the centrally located unaffected tissues.

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