Silver fluorescent x-ray yield and its influence on the dose rate constant for nine low-energy brachytherapy source models.
Silver fluorescent x-ray yield and its influence on the dose rate constant for nine low-energy brachytherapy source models.
复制标题
九种低能量近距离放射治疗源模型的银荧光 X 射线产量及其对剂量率常数的影响。
DOI：
10.1118/1.2775665
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发表时间：
2007
期刊：
影响因子：
3.8
通讯作者：
Chen,ZheJay
中科院分区：
文献类型：
--
作者：
Nath,Ravinder;Chen,ZheJay
低能量近距离放射治疗源发射的光子的物理特性在很大程度上取决于源的结构。除了内部结构和源封装引起的吸收和散射之外，某些类型的源结构材料中发生的光电相互作用可以产生额外的能量特征x射线，其能量与裸放射性核素发射的能量不同。因此，封装在不同源模型中的相同放射性核素可能会导致剂量率常数和其他剂量测定参数彼此显着不同。这项工作的目的是对九种已知含银源产生的银荧光 X 射线的产量及其对剂量率常数的影响进行系统研究。使用高分辨率锗光谱仪，测量了九个源在其平分线上发射的相对光谱，发现彼此相似（相对强度的最大变化小于4%）。另一方面，测量的银荧光 X 射线光谱在不同模型之间表现出更大的变化；测量的相对强度的最大变化超过95%。所测量的银荧光 X 射线产额的较大变化是由于 (1) 在不同源模型中直接暴露于放射性核素的银量不同以及 (2) 源的内部几何形状对银荧光 X 射线的影响更大。由于添加银荧光 X 射线可以显着改变放射源发射的光子特性，因此在源固有剂量特性的理论计算中需要对银荧光 X 射线产率的精确了解。这项研究的结论是，银荧光产量的差异是在这些源模型中观察到的可变剂量率常数的主要原因。
The physical characteristics of the photons emitted by a low‐energy brachytherapy source are strongly dependent on the source's construction. Aside from absorption and scattering caused by the internal structures and the source encapsulation, the photoelectric interactions occurred in certain type of source‐construction materials can generate additional energetic characteristic x rays with energies different from those emitted by the bare radionuclide. As a result, the same radionuclide encapsulated in different source models can result in dose rate constants and other dosimetric parameters that are strikingly different from each other. The aim of this work was to perform a systematic study on the yield of silver fluorescent x rays produced in nine sources that are known to contain silver and its impact on the dose‐rate constant. Using a high‐resolution germanium spectrometer, the relative spectra emitted by the nine sources on its bisector were measured and found to be similar to each other (the maximum variation in the relative intensity was less than 4%). On the other hand, the measured silver fluorescent x‐ray spectra exhibited much greater variations from model to model; the maximum change in the measured relative intensity was over 95%. This larger variation in the measured silver fluorescent x‐ray yield was caused by (1) the different amount of silver that was directly exposed to the radionuclide in different source models and (2) the stronger influence of the source's internal geometry on the silver fluorescent x rays. Because the addition of silver fluorescent x rays can significantly alter the photon characteristics emitted by the radioactive sources, a precise knowledge on the silver fluorescent x‐ray yield is needed in theoretical calculations of the sources’ intrinsic dosimetric properties. This study concludes that the differences in silver fluorescent yield are the primary causes of the variable dose rate constant observed among these source models.