Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, CH-1211 Geneva 4, Switzerland.
Med Phys. 2013 Oct;40(10):102502. doi: 10.1118/1.4819939.
Positron emission tomography (PET) plays an important role in the diagnosis, staging, treatment, and surveillance of clinically localized diseases. Combined PET/CT imaging exhibits significantly higher sensitivity, specificity, and accuracy than conventional imaging when it comes to detecting malignant tumors in children. However, the radiation dose from positron-emitting radionuclide to the pediatric population is a matter of concern since children are at a particularly high risk when exposed to ionizing radiation.
The authors evaluate the absorbed fractions and specific absorbed fractions (SAFs) of monoenergy photons/electrons as well as S-values of 9 positron-emitting radionuclides (C-11, N-13, O-15, F-18, Cu-64, Ga-68, Rb-82, Y-86, and I-124) in 48 source regions for 10 anthropomorphic pediatric hybrid models, including the reference newborn, 1-, 5-, 10-, and 15-yr-old male and female models, using the Monte Carlo N-Particle eXtended general purpose Monte Carlo transport code.
The self-absorbed SAFs and S-values for most organs were inversely related to the age and body weight, whereas the cross-dose terms presented less correlation with body weight. For most source/target organ pairs, Rb-82 and Y-86 produce the highest self-absorbed and cross-absorbed S-values, respectively, while Cu-64 produces the lowest S-values because of the low-energy and high-frequency of electron emissions. Most of the total self-absorbed S-values are contributed from nonpenetrating particles (electrons and positrons), which have a linear relationship with body weight. The dependence of self-absorbed S-values of the two annihilation photons varies to the reciprocal of 0.76 power of the mass, whereas the self-absorbed S-values of positrons vary according to the reciprocal mass.
The produced S-values for common positron-emitting radionuclides can be exploited for the assessment of radiation dose delivered to the pediatric population from various PET radiotracers used in clinical and research settings. The mass scaling method for positron-emitters can be used to derive patient-specific S-values from data of reference phantoms.
正电子发射断层扫描（PET）在诊断、分期、治疗和监测临床局限性疾病方面发挥着重要作用。与传统成像相比，当涉及到儿童恶性肿瘤的检测时，PET/CT 成像显示出更高的灵敏度、特异性和准确性。然而，由于儿童在接触电离辐射时处于特别高的风险，因此来自正电子发射放射性核素的辐射剂量是一个值得关注的问题。
作者评估了 10 种人体模型中的 48 个源区的单能光子/电子的吸收分数和特定吸收分数（SAF）以及 9 种正电子发射放射性核素（C-11、N-13、O-15、F-18、Cu-64、Ga-68、Rb-82、Y-86 和 I-124）的 S 值，包括参考新生儿、1 岁、5 岁、10 岁和 15 岁的男性和女性模型，使用蒙特卡罗 N 粒子扩展通用蒙特卡罗输运代码。
大多数器官的自吸收 SAF 和 S 值与年龄和体重呈反比，而交叉剂量项与体重的相关性较小。对于大多数源/靶器官对，Rb-82 和 Y-86 分别产生最高的自吸收和交叉吸收 S 值，而 Cu-64 由于电子发射的低能量和高频而产生最低的 S 值。大多数总自吸收 S 值来自非穿透粒子（电子和正电子），其与体重呈线性关系。两个湮没光子的自吸收 S 值的依赖性随质量的倒数 0.76 次方而变化，而正电子的自吸收 S 值则根据质量的倒数而变化。
所产生的常见正电子发射放射性核素的 S 值可用于评估临床和研究中使用的各种 PET 放射性示踪剂对儿科人群的辐射剂量。正电子发射器的质量缩放方法可用于从参考体模的数据中得出患者特异性 S 值。
