Purpose: Eye plaque brachytherapy provides excellent tumor control for uveal melanoma, however high doses to organs at risk (OAR) may cause unwanted side-effects. To overcome such toxicities, an extraocular shield plus intraocularly injected magnetic fluid is proposed. Magnetic fluid has been previously used clinically for the treatment of retinal detachment. Our approach uses a magnetic plaque to attract the fluid to cover the melanoma and shield adjacent OARs from excessive doses during treatment. Film measurements were performed to quantify the dose reduction afforded by our shield-magnetite system.
Methods: The height of a standard 20-mm I-125 COMS plaque was increased to allow placement of a custom concave magnet (NdFeB, N52-Grade) behind the silastic seed holder. 3D-printed eye phantoms were created with 3-, 5- and 8-mm tumor heights. EBT3 GafChromic film was calibrated with a single I-125 seed, used for the measurements, and analyzed with ImageJ (NIH, Bethesda, MD). 0.8 mL of magnetite fluid was added to the eye phantom and film measurements were performed in water with the film placed parallel to the plaque at 11.3 mm from the inner sclera (tumor base).
Results: At normal tissue locations, a small volume (0.8 mL) of fluid shielded 69% (3 mm) and 63% (5 mm) of the radiation. For larger tumors (8 mm), 0.8 mL of fluid produced a 53% dose reduction. When 1.8 mL of magnetite fluid was used, a 76% dose reduction was measured for large tumors.
Conclusion: A novel magnetic eye plaque effectively attracted magnetite fluid to surround an ocular melanoma and shield OARs by more than half. The shape of the magnet attracted more fluid to shield off-axis structures of the eye. This innovative shielding system could limit normal tissue toxicities and improve the quality of life for patients with uveal melanoma.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by an institutional Spark Grant, in addition to funds from Nanomedics, LLC.
Not Applicable / None Entered.