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首页> 外文期刊>Physics in medicine and biology. >Comparison of internal dosimetry factors for three classes of adult computational phantoms with emphasis on I-131 in the thyroid.
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Comparison of internal dosimetry factors for three classes of adult computational phantoms with emphasis on I-131 in the thyroid.

机译：三类成人计算模拟中的内部剂量测定因子对甲状腺I-131重点的比较。

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摘要

The S values for 11 major target organs for I-131 in the thyroid were compared for three classes of adult computational human phantoms: stylized, voxel and hybrid phantoms. In addition, we compared specific absorbed fractions (SAFs) with the thyroid as a source region over a broader photon energy range than the x- and gamma-rays of I-131. The S and SAF values were calculated for the International Commission on Radiological Protection (ICRP) reference voxel phantoms and the University of Florida (UF) hybrid phantoms by using the Monte Carlo transport method, while the S and SAF values for the Oak Ridge National Laboratory (ORNL) stylized phantoms were obtained from earlier publications. Phantoms in our calculations were for adults of both genders. The 11 target organs and tissues that were selected for the comparison of S values are brain, breast, stomach wall, small intestine wall, colon wall, heart wall, pancreas, salivary glands, thyroid, lungs and active marrow for I-131 and thyroid as a source region. The comparisons showed, in general, an underestimation of S values reported for the stylized phantoms compared to the values based on the ICRP voxel and UF hybrid phantoms and relatively good agreement between the S values obtained for the ICRP and UF phantoms. Substantial differences were observed for some organs between the three types of phantoms. For example, the small intestine wall of ICRP male phantom and heart wall of ICRP female phantom showed up to eightfold and fourfold greater S values, respectively, compared to the reported values for the ORNL phantoms. UF male and female phantoms also showed significant differences compared to the ORNL phantom, 4.0-fold greater for the small intestine wall and 3.3-fold greater for the heart wall. In our method, we directly calculated the S values without using the SAFs as commonly done. Hence, we sought to confirm the differences observed in our S values by comparing the SAFs among the phantoms with the thyroid as a source region for selected target organs--small intestine wall, lungs, pancreas and breast--as well as illustrate differences in energy deposition across the energy range (12 photon energies from 0.01 to 4 MeV). Differences were found in the SAFs between phantoms in a similar manner as the differences observed in S values but with larger differences at lower photon energies. To investigate the differences observed in the S and SAF values, the chord length distributions (CLDs) were computed for the selected source--target pairs and compared across the phantoms. As demonstrated by the CLDs, we found that the differences between phantoms in those factors used in internal dosimetry were governed to a significant degree by inter-organ distances which are a function of organ shape as well as organ location.
机译：将甲状腺I-131中的11个主要目标器官的S值与三类成人计算人体幻影进行比较：程式化，体素和杂化素。另外，我们将特异的吸收级分（SAF）与甲状腺相比，在较宽的光子能量范围内比I-131的X-和γ射线相比源区。根据国际放射性保护委员会（ICRP）参考体素和佛罗里达大学（UF）杂交幻影来计算S和SAF值，通过​​使用蒙特卡罗运输方法，而橡树岭国家实验室的S和SAF值（ornl）程式化的幽灵是从早期的出版物获得的。我们计算中的幽灵是两种性别的成年人。选择的11个靶器官和组织，用于比较S值是脑，乳房，胃壁，小肠壁，结肠壁，心脏壁，胰腺，唾液腺，甲状腺，肺和活性骨髓为I-131和甲状腺作为源区。一般而言之，与基于ICRP体素和UF杂化杂于的值相比，对风格化幽灵的值进行了低估了对风格化幽灵的值的低估，并且在为ICRP和UF幻像获得的S值之间的相对良好的一致性。对于三种类型的幽灵之间的一些器官观察到显着差异。例如，与报道的ORNL Phantoms的报道值相比，ICRP阳性模型的小肠壁和ICRP阴影的心脏骨骼和心脏壁分别显示出高达八倍和四倍的S值。与ORN1幻影相比，UF雄性和女性幽灵还表现出显着的差异，对于小肠壁，4.0倍，心脏壁更大3.3倍。在我们的方法中，我们直接计算了S值而不使用常用的SAF。因此，我们试图通过将含有甲状腺的含量与所选靶器官的源区进行比较来确认在我们的价值观中观察到的差异 - 小肠壁，肺，胰腺和乳房以及说明差异能量范围的能量沉积（12光子能量为0.01至4 meV）。在幽灵之间的SAF之间以与S值观察的差异类似的方式发现差异，但在较低光子能量下具有较大差异。为了研究S和SAF值中观察到的差异，为所选择的源 - 目标对计算和弦长度分布（CLD），并在幻像上比较。如CLD所示，我们发现内部剂量测定中使用的那些因素之间的幽灵之间的差异受到器官距离的显着程度，这是器官形状以及器官位置的函数。

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