Program Information
Enhanced Shielding Effect of Intraocular Silicone Oil in Plaque Brachytherapy Using of Pd-103: A Monte Carlo Investigation
YM Yang1*, P Chow1 , T McCannel2 , J Lamb1 , (1) Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, USA (2)Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles, Los Angeles, CA, USA
Presentations
SU-E-205-6 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 205
Purpose: Eye plaque brachytherapy for ocular melanoma has been shown to be an effective treatment, with studies reporting 90+% local control. However, complications include retinopathy and neuropathy resulting in loss of vision. Intra-ocular silicone oil, used during iodine 125 (I-125) plaque brachytherapy, reduces dose to critical structures. Separately, Palladium 103 (Pd-103) has been used for plaque brachytherapy in some clinics because of its faster dose falloff beyond the tumor. In this study we combine the lower energy Pd-103 sources and silicone oil to achieve greater reduction of dose to normal tissues relative to tumor dose.
Methods: The Geant4 v10.03 Monte Carlo toolkit was used to simulate a 24 mm spherically symmetric globe containing a 10 mm height ocular tumor, and a 23 mm gold eye plaque. Sources were modeled after commercially available I-125 and Pd-103 seeds. Vitreous humor was simulated with either water or 1000-centistoke silicone oil, with the tumor being water-equivalent in either scenario. Tumor apex dose was normalized to 85 Gy. The following hypothetical treatments were evaluated: I-125 seeds and water-filled globe, I-125 and oil-filled globe, Pd-103 and water, and Pd-103 and oil.
Results: Dose to the inner eye surface outside the treatment area was lower with Pd-103 and an oil-filled globe compared to the other three scenarios: at 6 mm from the plaque edge, the dose was 20 Gy with Pd-103 and oil, in contrast with 30 Gy with Pd-103 and water, 30 Gy with I-125 and oil, and 35 Gy with I-125 and water. As expected, dose in the area covered by the plaque was greatest with the combination of Pd-103 and oil.
Conclusion: The utilization of Pd-103 seeds and intra-ocular silicone oil placement has the potential to lead to improved sparing of critical structures beyond the edge of the plaque compared to commonly-used plaque techniques.
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