Probability of Radiation Induced Maculopathy and Optic Neuropathy Following I-125 Eye Plaque Brachytherapy
M Studenski1*, V Peters2, A Gurayah2, W Jin1, D Kwon3, W Zhao3, Z Correa4, J Harbour5, S Samuels1, (1) Department of Radiation Oncology, University of Miami Sylvester Comprehensive Cancer Center, Miami, FL, (2) University Of Miami Miller School Of Medicine, Miami, FL, (3) Department of Biostatistics and Bioinformatics, University Of Miami Miller School Of Medicine, Miami, FL, (4) Department of Ophthalmology, University of Miami Bascom Palmer Eye Institute, Miami, FL, (5) Department of Ophthlmology, UT Southwestern Medical Center, Dallas, TX
Presentations
PO-GePV-T-38 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Determine the probability of radiation induced maculopathy and optic neuropathy following I-125 eye plaque brachytherapy using modern treatment planning software.
Methods: An IRB approve retrospective chart review analyzed 109 patients treated with I-125 eye plaque brachytherapy from 5/2016-12/2018. All patients were planned using IsoAid Plaque Simulator (Eye Physics, LLC., Los Alamitos, CA) and had at least 3 months of follow-up. Radiation toxicity was defined as an event of maculopathy or optic neuropathy as determined by the attending ophthalmologist. Toxicity was coded as a binary variable. We collected the macula and optic disc maximum and mean dose from post-implant dosimetry and calculated the probability of toxicity for each endpoint.
Results: The average max and mean dose to the macula was 64.3 Gy (8.3-268.8 Gy) and 37.7 Gy (6.1-167.4 Gy), respectively. 57 patients (52.3%) experienced maculopathy. The average max and mean dose to the optic disc was 21.8 Gy (7.9-120.7 Gy) and 16.92 Gy (7.0-93.0 Gy), respectively. 22 patients (20.2%) experienced optic neuropathy. The probability of maculopathy sharply increased from zero to the maximum of 52% at a mean macula dose of 15 Gy and a max dose of 25 Gy. The probability of optic neuropathy increased sharply from zero to the maximum of 20% around 30 Gy mean and 35 Gy max dose to the optic disc. At higher doses, the probability flattened and did not increase further.
Conclusion: The probability of radiation induced maculopathy occurs at a lower threshold dose than optic neuropathy following eye plaque brachytherapy. For both toxicities, the probability does not increase beyond the initial spike so tumor coverage should not be sacrificed during planning if the dose exceeds this threshold.
Keywords
Brachytherapy, Eye Plaques, Dosimetry
Taxonomy
TH- Brachytherapy: General (most aspects)
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