Maziar Asghar, Paydar Reza, Azadbakht Ghazal, Shahbazi-Gahrouei Daryoush
Department of Radiation Sciences, Radiation Biology Research Centre, School of Allied Medicine, Iran University of Medical Sciences, Tehran, Iran.
Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
J Med Signals Sens. 2019 Aug 29;9(3):190-195. doi: 10.4103/jmss.JMSS_40_18. eCollection 2019 Jul-Sep.
Thyroid exposure to radiation in brain computed tomography (CT) scan is of great value since it is considered as a vital organ. This study aimed to investigate the absorbed dose of thyroid by various protocols of head CT in patients referring to 64-slice CT scan center and to compare the values with the calculated dose by imaging performance and assessment of CT (ImPACT) method. Also, the values of CT scan dose index (CTDI) were calculated with semiconductor detector. In this cross-sectional study, 120 outpatients including three groups of forty individuals over 40 years old referring to the hospital radiology centers in Tehran for head CT were chosen and 3 thermo-luminescence dosimeter (TLD-GR200) were applied on thyroid gland of each patient. For brain CT, Absorbed and effective doses of thyroid gland were calculated by ImPACT software. In addition, semiconductor detector in head CTDI phantom calculated CTDI for the applied protocols. Mean effective dose of thyroid gland in brain scan group was calculated by TLD and ImPACT software which showed no significant difference ( < 0.001). Mean effective dose of thyroid gland in unidirectional and bi-directional sinus scan by TLD and ImPACT software were different significantly ( < 0.001). Also, the differences between CTDI values shown by brain and sinus scan protocol with semiconductor detector and those CTDI were significant ( < 0.001). The calculated values of absorbed dose and effective doses of thyroid by TLD and ImPACT software were not significantly different. Mean effective dose calculated for thyroid gland in head scans by TLD and ImPACT was less than the annual permissive level for thyroid gland suggested by International Committee on Radiological Protection. In this study, calculated values of thyroid effective dose in brain scan with 64-slice scanner were less than the calculated values in a similar study.
由于甲状腺被视为重要器官，因此在脑部计算机断层扫描（CT）中甲状腺的辐射暴露具有重要意义。本研究旨在调查前往64层CT扫描中心就诊的患者通过各种头部CT方案时甲状腺的吸收剂量，并将这些值与通过CT成像性能与评估（ImPACT）方法计算出的剂量进行比较。此外，还使用半导体探测器计算了CT扫描剂量指数（CTDI）的值。在这项横断面研究中，选择了120名门诊患者，包括三组，每组40名40岁以上前往德黑兰医院放射科进行头部CT检查的患者，并在每位患者的甲状腺上放置3个热释光剂量计（TLD-GR200）。对于脑部CT，通过ImPACT软件计算甲状腺的吸收剂量和有效剂量。此外，头部CTDI体模中的半导体探测器针对所应用的方案计算CTDI。通过TLD和ImPACT软件计算出脑部扫描组中甲状腺的平均有效剂量，结果显示无显著差异（<0.001）。通过TLD和ImPACT软件计算出的单向和双向鼻窦扫描中甲状腺的平均有效剂量有显著差异（<0.001）。此外，脑部和鼻窦扫描方案通过半导体探测器显示的CTDI值与那些CTDI之间存在显著差异（<0.001）。TLD和ImPACT软件计算出的甲状腺吸收剂量和有效剂量的数值无显著差异。通过TLD和ImPACT计算出的头部扫描中甲状腺的平均有效剂量低于国际放射防护委员会建议的甲状腺年度允许剂量水平。在本研究中，64层扫描仪脑部扫描中甲状腺有效剂量的计算值低于类似研究中的计算值。
