University of California, Los Angeles, 200 Medical Plaza Ste B265, Los Angeles, CA, 90095, USA.
Department of Ophthalmology, Stein Eye and Doheny Eye Institutes, University of California, 100 Stein PLZ, Los Angeles, CA, 90095, USA.
Med Phys. 2019 Feb;46(2):1006-1011. doi: 10.1002/mp.13341. Epub 2019 Jan 4.
Episcleral eye plaques provide excellent local control of ocular melanoma, but vision sparing remains a significant problem with 30% or more of patients experiencing significant visual acuity degradation. The use of silicone oil shielding with Iodine-125 plaques has previously been reported to improve critical structure sparing. We hypothesized that the use of Palladium-103 would improve the shielding effectiveness of silicone oil due to the strong energy dependence of the photoelectric effect. This Monte Carlo simulation study reports a comparison of the shielding effects of silicone oil when used in conjunction with Pd-103 and with I-125 plaques.
GEANT4 was used to simulate eye plaque treatments to an eye with either water-equivalent vitreous humor, or silicone oil in place of the vitreous humor. Two solid gold plaques, 15 and 23 mm, were simulated loaded with I-125 and with Pd-103 source seeds. Seed activity was normalized such that 85 Gy was delivered to the tumor apex in the water-equivalent cases. Tumor apex dose, central axis dose, and inner sclera dose reductions with silicone oil were evaluated.
Silicone oil resulted in an underdosing to the tumor apex of 6.1% and 7.5% in the 15 mm plaque for I-125 and Pd-103, respectively, and 3.4% and 4.3% in the 23 mm plaque for I-125 and Pd-103, respectively. When renormalized to 85 Gy to the tumor apex in all scenarios, silicone oil reduced the dose to the inner sclera 90° from the plaque by 19-32% for the 15 and 23 mm plaques using I-125, and by 33-65% for the 15 and 23 mm plaques using Pd-103.
The combination of silicone oil and Pd-103 eye plaques offers the potential for greatly improved sparing to normal structures compared to Pd-103 plaques alone or I-125 plaques with or without silicone oil.
巩膜眼贴可极好地控制眼黑色素瘤，但保留视力仍然是一个重大问题，超过 30%的患者会出现明显的视力下降。先前有报道称，使用碘-125 眼贴时使用硅油屏蔽可改善关键结构的保留。我们假设，由于光电效应的能量依赖性很强，钯-103 的使用会提高硅油的屏蔽效果。这项蒙特卡罗模拟研究报告了比较在使用硅油时与钯-103 和碘-125 眼贴联合使用的屏蔽效果。
使用 GEANT4 模拟了眼贴治疗带有水当量玻璃体或硅油替代玻璃体的眼睛。模拟了两个 15 和 23 毫米厚的纯金眼贴，分别装载碘-125 和钯-103 源种子。将种子活性归一化，以使水当量情况下肿瘤顶点达到 85Gy。评估了硅油对肿瘤顶点剂量、中心轴剂量和内巩膜剂量的降低作用。
硅油导致肿瘤顶点剂量不足分别为碘-125 和钯-103 的 15mm 眼贴 6.1%和 7.5%，23mm 眼贴 3.4%和 4.3%。在所有情况下将肿瘤顶点重新归一化为 85Gy 时，硅油将内巩膜与眼贴成 90°角的剂量降低了 19-32%，用于碘-125 的 15 和 23mm 眼贴，以及 33-65%，用于钯-103 的 15 和 23mm 眼贴。
与单独使用钯-103 眼贴或使用或不使用硅油的碘-125 眼贴相比，硅油和钯-103 眼贴的组合为正常结构提供了大大改善的保留潜力。
