Accurate estimation of dose distributions inside an eye irradiated with 106Ru plaques
Accurate estimation of dose distributions inside an eye irradiated with 106Ru plaques
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DOI：
10.1007/s00066-012-0245-6
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发表时间：
2013-01-01
影响因子：
3.1
通讯作者：
Sauerwein, W.
中科院分区：
文献类型：
--
作者：
Brualla, L.;Sempau, J.;Sauerwein, W.
眼内肿瘤的照射需要专门的技术，例如使用 Ru-106 斑块进行近距离放射治疗。目前可用的治疗计划系统依赖于眼睛是均匀水球的假设和简化的辐射传输物理学。然而，准确的剂量分布及其评估需要更好的眼睛和物理模型。蒙特卡罗代码 PENELOPE 可以方便地模拟 Ru-106 经过 Rh-106 的 β 衰变变成 Pd-106，用于基于患者眼睛的计算机断层扫描来模拟辐射传输。制造商 BEBIG 的两个斑块（型号 CCA 和 CCB）的详细几何描述嵌入到计算机断层扫描中。首先通过与水体模中的实验结果进行比较来验证模拟。计算了眼球上三个斑块位置的剂量图。根据这些图，评估了眼睛和危险结构的等剂量曲线和累积剂量体积直方图。例如，据观察，用于治疗后部肿瘤的CCA斑块的后部放置相对于后部放置4毫米，接收超过80Gy的视盘体积将从40％减少至0％。解剖位置的如此微小的差异会导致剂量的变化，这对副作用至关重要，尤其是在视力方面。放射肿瘤学家必须引起外科医生注意处于危险的结构中吸收剂量的这些巨大变化，特别是当斑块必须靠近相关组织放置时。在计算机分段断层扫描中准确模拟了真实患者模型的眼斑的详细几何形状。以前所未有的精度获得了眼睛和眼眶相关解剖结构的剂量体积直方图。这代表着优化眼部肿瘤近距离放射治疗的重要一步。
Irradiation of intraocular tumors requires dedicated techniques, such as brachytherapy with Ru-106 plaques. The currently available treatment planning system relies on the assumption that the eye is a homogeneous water sphere and on simplified radiation transport physics. However, accurate dose distributions and their assessment demand better models for both the eye and the physics.The Monte Carlo code PENELOPE, conveniently adapted to simulate the beta decay of Ru-106 over Rh-106 into Pd-106, was used to simulate radiation transport based on a computerized tomography scan of a patient's eye. A detailed geometrical description of two plaques (models CCA and CCB) from the manufacturer BEBIG was embedded in the computerized tomography scan.The simulations were firstly validated by comparison with experimental results in a water phantom. Dose maps were computed for three plaque locations on the eyeball. From these maps, isodose curves and cumulative dose-volume histograms in the eye and for the structures at risk were assessed. For example, it was observed that a 4-mm anterior displacement with respect to a posterior placement of a CCA plaque for treating a posterior tumor would reduce from 40 to 0% the volume of the optic disc receiving more than 80 Gy. Such a small difference in anatomical position leads to a change in the dose that is crucial for side effects, especially with respect to visual acuity. The radiation oncologist has to bring these large changes in absorbed dose in the structures at risk to the attention of the surgeon, especially when the plaque has to be positioned close to relevant tissues.The detailed geometry of an eye plaque in computerized and segmented tomography of a realistic patient phantom was simulated accurately. Dose-volume histograms for relevant anatomical structures of the eye and the orbit were obtained with unprecedented accuracy. This represents an important step toward an optimized brachytherapy treatment of ocular tumors.