Thomson R M, Taylor Rep, Rogers Dwo
Department of Physics, Carleton University, Ottawa, Canada.
Med Phys. 2008 Jul;35(7Part3):3416. doi: 10.1118/1.2965995.
A Monte Carlo study of dosimetry for eye plaque brachytherapy was performed. BrachyDose, an EGSnrc user-code which makes use of Yegin's multi-geometry package, was used to fully model Iodine-125 (model 6711) and Palladium-103 (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three-dimensional dose distributions in the eye region were obtained. In general, dose to water was scored, however the implications of replacing water with eye materials was explored. The effect of the gold alloy (Modulay) backing was investigated and the dose was found to be sensitive to the elemental composition of the backing. The presence of the silicon polymer (Silastic) seed carrier resulted in substantial dose decreases relative to water, particularly for Pd-103. For the Modulay backing and Silastic insert combination in a 20 mm plaque, the dose decrease relative to water is of the order of 12% for I-125 and 20% for Pd-103 at a distance of 1 cm from the central seed along the plaque's central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaque's position within the eye and the source type. The dose distributions in the eye for the two different sources were compared and, for the same prescription dose, Pd-103 generally offers a lower dose to critical normal structures.
开展了一项关于眼部敷贴近距离放射治疗剂量测定的蒙特卡罗研究。使用了BrachyDose，这是一个利用Yegin多几何包的EGSnrc用户代码，用于对碘 - 125（6711型）和钯 - 103（200型）近距离放射治疗种子以及协作性眼黑色素瘤研究（COMS）的标准化敷贴进行完整建模。获得了眼部区域的三维剂量分布。一般来说，对水的剂量进行了计分，不过也探讨了用眼部材料替代水的影响。研究了金合金（Modulay）背衬的作用，发现剂量对背衬的元素组成敏感。硅聚合物（Silastic）种子载体的存在导致相对于水的剂量大幅降低，尤其是对于钯 - 103。对于20毫米敷贴中的Modulay背衬和Silastic插入物组合，在沿敷贴中心轴距中心种子1厘米处，相对于水的剂量降低对于碘 - 125约为12%，对于钯 - 103约为20%。对于COMS敷贴中使用的种子配置，种子间衰减在眼部区域内影响较小。引入空气界面会导致其附近剂量降低，这取决于敷贴在眼内的位置和源类型。比较了两种不同源在眼部的剂量分布，对于相同的处方剂量，钯 - 103通常对关键正常结构的剂量较低。
