M Ur Rehman¹*, R Hamilton², B Stea³, T Johnson⁴, L Furenlid⁵, B Miller⁶, (1) University of Arizona, Tucson, AZ, (2) University of Arizona, Tucson, AZ, (3) University Of Arizona, ,,(4) Banner University Medical Center, Tucson, AZ, (5) University Of Arizona, ,,(6) University of Arizona / Banner University Medical Center Tucson, Tucson, AZ

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  M Ur Rehman

TU-J430-BReP-F3-1 (Tuesday, 7/12/2022) 4:30 PM - 5:30 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: Localized plaque radiation therapy of intraocular (uveal) melanoma is as effective as enucleation for medium sized choroidal melanoma, with the added advantage of eye and vision preservation. Radioactive seeds (Iodine-125) are attached to one side of a gold disk (plaque), which is sutured on the sclera at the location of the tumor. Typical eye-plaque activity verification is performed using a well-type chamber to confirm that seed activity is within 5% of the vendor-specified activity. Prefabricated eye plaques arrive in sterile packaging, which impedes direct on-site verification of individual seeds. Also, there is no independent existing method to determine a manufacturing error, for example, accidental placement of a cold seed. Instead, end-users rely on a separately supplied calibration seed that is measured and compared with vendor documentation. This work presents a novel rapid gamma-ray imaging and quantification method to confirm both the spatial distribution of the seeds and non-invasively measure seed activities without disrupting the sterilized packaging.

Methods: A high-resolution, real-time digital scintigraphy system called iQID (ionizing-radiation Quantum Imaging Detector) was used to measure the spatial distribution and activity of seeds in a 14 mm eye plaque in a proof-of-concept experiment. Using a calibration seed of known activity, scintigraphy images were obtained for individual seed positions within the plaque. Activity was estimated based on the seed position and number of counts acquired.

Results: Live imaging of the plaque showed accurate placement at the predefined spatial positions, whereas no activity was measured after 10 hours of exposure with Gafchromic film. Our approach yielded an estimated average activity within 5% of the vendor reported activity.

Conclusion: Our novel approach of using high-resolution gamma-ray scintigraphy for QA of eye plaques provides a rapid, independent method to verify seed placement and activity without disturbing sterile packing. A high-performance collimator may improve results.

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