Huang Yuliang, Du Yi, Li Chenguang, Wang Haiyang, Zu Zhixin, Feng Zhongsu, Zhou Shun, Wu Hao, Zhang Yibao
Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Radiation Oncology, Peking University Cancer Hospital & Institute, Beijing 100142 People's Republic of China.
J Radiol Prot. 2019 Sep;39(3):739-748. doi: 10.1088/1361-6498/ab1e74. Epub 2019 May 1.
Medical exposure to ionizing irradiation has become a recognised carcinogenic risk. Balancing the concomitant imaging dose and positioning accuracy is critical in image-guided-radiotherapy (IGRT) especially for children, whose higher biological susceptibility and longer expected life make them more vulnerable to develop secondary cancer. This work aims to evaluate and benchmark the imaging dose and positioning accuracy of a new MV cone-beam-CT (CBCT)-guided IGRT system, Varian Halcyon, against conventional kV CBCT. Weighted-CT-dose-index (CTDI) were measured for Varian TrueBeam kV CBCT, and computed for Halcyon MV CBCT using Eclipse system as validated before. Simulating the IGRT workflow, the positioning accuracy of correcting a known shift was tested on various regions of 1-year, 5-year and adult anthropomorphic phantoms, respectively. Inter-scanner and inter-protocol comparisons of dose and accuracy were performed. kV CTDI for 'Head', 'Thorax', 'Pelvis' and 'Image Gently' (in CTDI/CTDI phantoms, respectively) protocols were measured as 4.5 mGy, 5.4 mGy, 19.3 mGy, and 1.1 mGy/0.5 mGy, respectively. Using 'High Quality' mode, MV CTDI in the CTDI and CTDI phantoms were computed as 84.5 mGy and 63.8 mGy (imaging length = 28 cm), 68.8 mGy and 55.5 mGy (imaging length = 16 cm), respectively, which were about twice of 'Low Dose' mode. The maximum positioning deviation observed on Halcyon was 0.51 mm ('Low Dose' adult thorax), which was lower than that of standard (0.58 mm, 'Pelvis' adult pelvis) and 'Image Gently' kV CBCT (1.57 mm, adult pelvis). Accuracy of 'Image Gently' kV CBCT head & neck and thoracic imaging were clinically acceptable for adults (maximum deviation = 0.54 mm, adult thorax). Complying with Image Gently campaign, dose-efficient protocols should be used for pediatric IGRT, achieving comparable positioning accuracy on the new Halcyon MV CBCT system relative to the conventional kV CBCT.
医疗中接受电离辐射已被公认为一种致癌风险。在图像引导放射治疗（IGRT）中，尤其是对于儿童，平衡伴随的成像剂量和定位精度至关重要，因为儿童较高的生物易感性和较长的预期寿命使他们更容易患继发性癌症。这项工作旨在评估并对比一种新型兆伏级锥形束CT（CBCT）引导的IGRT系统瓦里安Halcyon与传统千伏级CBCT的成像剂量和定位精度。对瓦里安TrueBeam千伏级CBCT测量加权CT剂量指数（CTDI），并使用之前经验证的Eclipse系统计算Halcyon兆伏级CBCT的CTDI。模拟IGRT工作流程，分别在1岁、5岁和成人人体模型的各个部位测试校正已知移位的定位精度。进行了不同扫描仪之间以及不同协议之间的剂量和精度比较。“头部”“胸部”“骨盆”和“轻柔成像”（分别在CTDI/CTDI模型中）协议的千伏级CTDI测量值分别为4.5毫戈瑞、5.4毫戈瑞、19.3毫戈瑞和1.1毫戈瑞/0.5毫戈瑞。在“高质量”模式下，CTDI模型和CTDI 模型中的兆伏级CTDI计算值分别为84.5毫戈瑞和63.8毫戈瑞（成像长度 = 28厘米）、68.8毫戈瑞和55.5毫戈瑞（成像长度 = 16厘米），约为“低剂量”模式的两倍。在Halcyon上观察到的最大定位偏差为0.51毫米（“低剂量”成人胸部），低于标准（0.58毫米，“骨盆”成人骨盆）和“轻柔成像”千伏级CBCT（1.57毫米，成人骨盆）。“轻柔成像”千伏级CBCT头部、颈部和胸部成像的精度对于成人来说在临床上是可接受的（最大偏差 = 0.54毫米，成人胸部）。遵循“轻柔成像”行动，儿童IGRT应采用高效低剂量协议，在新的Halcyon兆伏级CBCT系统上实现与传统千伏级CBCT相当的定位精度。
