Room: Exhibit Hall | Forum 7
Purpose: Age-related macular degeneration (AMD) is the leading cause of blindness in aging adults and affects millions of U.S. patients and even more worldwide. As a radiotherapy solution, the iWandÂ® brachytherapy device uses Y-90, and its emissions are dosimetrically compared to other beta-emitting radionuclides.
Methods: The iWand source is a 6mm diameter Ti capsule that is 1mm in height and contains a 5.5mm diameter Y-90 source that is 0.5mm thick. For comparison, Y-90 in the capsule was substituted for three other radionuclides: Sr-90, Rh-106/Ru-106, and P-32. Sr-90 and Y-90 doses were combined for gleaning Sr-90/Y-90 results. Dose was calculated using MCNP6 with photon:electron coupling in a 5cm radius water phantom and 0.01cm voxels. The source and sampling geometry were cylindrically-symmetric with dose estimated in contact with the capsule out to a 2.0cm radius. 10â?¸ simulations for each radionuclide produced Type A uncertainties <0.2% at the capsule surface. Dose components (beta and photon) were estimated, the total dose distributions were normalized at 2mm from the capsule surface along its CAX, and the four radionuclides were compared.
Results: Relative to the prescription point, maximum surface total doses were 3.8, 2.9, and 6.5 for Y-90, Ru-106/Rh-106, and P-32, respectively. For Sr-90, the beta dose was at most 0.4% of Y-90 and the photon dose was similar to Y-90, albeit both photon doses were 3 orders of magnitude lower than the Y-90 beta dose. As normalized to the prescription point, all photon doses were highest in contact with the capsule along the CAX and were 0.31%, 0.55%, and 0.34% for Y-90, Ru/Rh-106, and P-32, respectively. Photon doses decreased to 0.08%, 0.15%, 0.07% at a depth of 2mm.
Conclusion: Based on its half-life, maximum beta energy, and dose distribution, the Y-90 iWand was the best beta-emitting source for brachytherapy of AMD with favorable dosimetric features.
Funding Support, Disclosures, and Conflict of Interest: Dr. Rivard and the coauthors are partners of LV Liberty Vision Corp. (Portsmouth, NH), manufacturer of an ocular brachytherapy device examined in this study.