Johnson Jedediah E, Deufel Christopher L, Furutani Keith M
Department of Radiation Oncology, Mayo Clinic, Rochester, MN.
Department of Radiation Oncology, Mayo Clinic, Rochester, MN.
Brachytherapy. 2016 Sep-Oct;15(5):661-8. doi: 10.1016/j.brachy.2016.06.002. Epub 2016 Jul 27.
To quantify the dosimetric effects of random and systematic seed position uncertainties in Collaborative Ocular Melanoma Study-based eye plaques.
An eye plaque dose calculation routine was created using Task Group 43 formalism. A variety of clinical configurations were simulated, including two seed models: (125)I and (103)Pd, three eye plaque sizes, and eight plaque/eye orientations. Dose was calculated at four ocular anatomic sites and three central axis plaque depths. Random seed positional uncertainty was modeled by adding Gaussian random displacements, in one of three seed-motion degrees of freedom, to each seed's nominal coordinate. Distributions of dosimetric outcomes were obtained and fitted after 10(6) randomizations. Similar analysis was performed for deterministic, systematic shifts of the plaque along the eye surface and radially from the globe center.
Random seed placement uncertainties of 0.2-mm root mean square (RMS) (amplitude) produce dose changes that are typically <4% for each degree of freedom (95% confidence interval). Systematic seed placement uncertainties are generally greater than random uncertainty 95% confidence intervals (factor of 0.72-2.15), with the relative magnitudes depending on plaque size and location of interest. Eye plaque dosimetry is most sensitive to seed movement toward the center of the eye. Dosimetric uncertainty also increases with increasing dose gradients, which are typically greatest near the inner sclera, with smaller plaques, and with lower energy radionuclides (e.g., (103)Pd).
Dosimetric uncertainties due to the random seed positional displacements anticipated in the clinic are expected to be <4% for each degree of freedom in most circumstances.
量化基于协作性眼黑色素瘤研究的眼敷贴中随机和系统的籽源位置不确定性的剂量学效应。
使用任务组43形式主义创建了一个眼敷贴剂量计算程序。模拟了多种临床配置，包括两种籽源模型：碘-125和钯-103，三种眼敷贴尺寸，以及八种敷贴/眼睛方向。在四个眼部解剖部位和三个中心轴敷贴深度处计算剂量。通过在三个籽源运动自由度之一中向每个籽源的标称坐标添加高斯随机位移来模拟随机籽源位置不确定性。在10^6次随机化后获得并拟合剂量学结果的分布。对敷贴沿眼表面和从眼球中心径向的确定性、系统性移位进行了类似分析。
均方根（RMS）（幅度）为0.2毫米的随机籽源放置不确定性产生的剂量变化对于每个自由度通常<4%（95%置信区间）。系统性籽源放置不确定性通常大于随机不确定性的95%置信区间（0.72 - 2.15倍），相对大小取决于敷贴尺寸和感兴趣的位置。眼敷贴剂量学对籽源向眼中心移动最为敏感。剂量学不确定性也随着剂量梯度的增加而增加，剂量梯度通常在内巩膜附近、较小敷贴以及较低能量放射性核素（例如钯-103）的情况下最大。
在大多数情况下，临床预期的随机籽源位置位移导致的剂量学不确定性对于每个自由度预计<4%。
