Giansante Louise, Martins Juliana C, Nersissian Denise Y, Kiers Karen C, Kay Fernando U, Sawamura Marcio V Y, Lee Choonsik, Gebrim Eloisa M M S, Costa Paulo R
Group of Radiation Dosimetry and Medical Physics, Institute of Physics, University of São Paulo (IFUSP), São Paulo, SP, Brazil.
Ludwig-Maximilians-Universität München (LMU), Munich, Germany.
J Appl Clin Med Phys. 2019 Jan;20(1):308-320. doi: 10.1002/acm2.12505. Epub 2018 Dec 3.
To evaluate organ doses in routine and low-dose chest computed tomography (CT) protocols using an experimental methodology. To compare experimental results with results obtained by the National Cancer Institute dosimetry system for CT (NCICT) organ dose calculator. To address the differences on organ dose measurements using tube current modulation (TCM) and fixed tube current protocols.
An experimental approach to evaluate organ doses in pediatric and adult anthropomorphic phantoms using thermoluminescent dosimeters (TLDs) was employed in this study. Several analyses were performed in order to establish the best way to achieve the main results in this investigation. The protocols used in this study were selected after an analysis of patient data collected from the Institute of Radiology of the School of Medicine of the University of São Paulo (InRad). The image quality was evaluated by a radiologist from this institution. Six chest adult protocols and four chest pediatric protocols were evaluated. Lung doses were evaluated for the adult phantom and lung and thyroid doses were evaluated for the pediatric phantom. The irradiations were performed using both a GE and a Philips CT scanner. Finally, organ doses measured with dosimeters were compared with Monte Carlo simulations performed with NCICT.
After analyzing the data collected from all CT examinations performed during a period of 3 yr, the authors identified that adult and pediatric chest CT are among the most applied protocol in patients in that clinical institution, demonstrating the relevance on evaluating organ doses due to these examinations. With regards to the scan parameters adopted, the authors identified that using 80 kV instead of 120 kV for a pediatric chest routine CT, with TCM in both situations, can lead up to a 28.7% decrease on the absorbed dose. Moreover, in comparison to the standard adult protocol, which is performed with fixed mAs, TCM, and ultra low-dose protocols resulted in dose reductions of up to 35.0% and 90.0%, respectively. Finally, the percent differences found between experimental and Monte Carlo simulated organ doses were within a 20% interval.
The results obtained in this study measured the impact on the absorbed dose in routine chest CT by changing several scan parameters while the image quality could be potentially preserved.
采用实验方法评估常规及低剂量胸部计算机断层扫描（CT）方案中的器官剂量。将实验结果与美国国立癌症研究所CT剂量测定系统（NCICT）器官剂量计算器所得结果进行比较。探讨使用管电流调制（TCM）和固定管电流方案时器官剂量测量的差异。
本研究采用实验方法，使用热释光剂量计（TLD）评估儿童和成人仿真人体模型中的器官剂量。进行了多项分析，以确定实现本研究主要结果的最佳方法。本研究中使用的方案是在分析从圣保罗大学医学院放射学研究所（InRad）收集的患者数据后选定的。图像质量由该机构的一名放射科医生评估。评估了六个成人胸部方案和四个儿童胸部方案。对成人模型评估肺部剂量，对儿童模型评估肺部和甲状腺剂量。使用GE和飞利浦CT扫描仪进行扫描。最后，将剂量计测量的器官剂量与使用NCICT进行的蒙特卡罗模拟结果进行比较。
在分析了3年期间所有CT检查收集的数据后，作者发现成人和儿童胸部CT是该临床机构中对患者应用最多的方案之一，表明评估这些检查所致器官剂量的相关性。关于所采用的扫描参数，作者发现，对于儿童胸部常规CT，在两种情况下均采用TCM，使用80 kV而非120 kV可使吸收剂量降低多达28.7%。此外，与采用固定mAs的标准成人方案相比，TCM和超低剂量方案分别使剂量降低多达35.0%和90.0%。最后，实验和蒙特卡罗模拟的器官剂量之间的百分比差异在20%的区间内。
本研究获得的结果测量了在可能保持图像质量的同时，通过改变多个扫描参数对常规胸部CT吸收剂量的影响。
