[1]田源,李明辉,张可,等.磁共振加速器Unity的输出量测量[J].中国医学物理学杂志,2021,38(11):1365-1370.[doi:DOI:10.3969/j.issn.1005-202X.2021.11.009]
　TIAN Yuan,LI Minghui,ZHANG Ke,et al.Output measurement of Unity MR-linac[J].Chinese Journal of Medical Physics,2021,38(11):1365-1370.[doi:DOI:10.3969/j.issn.1005-202X.2021.11.009]
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磁共振加速器Unity的输出量测量()
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《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]

卷:
38卷
期数:
2021年第11期
页码:
1365-1370
栏目:
医学放射物理
出版日期:
2021-11-26

文章信息/Info

Title:
Output measurement of Unity MR-linac
文章编号:
1005-202X（2021）11-1365-06
作者:
田源; 李明辉; 张可; 门阔; 戴建荣
国家癌症中心/国家肿瘤临床医学研究中心/中国医学科学院北京协和医学院肿瘤医院放疗科， 北京 100021
Author(s):
TIAN Yuan;  LI Minghui;  ZHANG Ke;  MEN Kuo;  DAI Jianrong
National Cancer Center/National Clinical Research Center for Cancer/Department of Radiation Oncology, Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
关键词:
磁共振加速器; Unity; 输出量; 电子射野影像装置; 日检; 长期稳定性
Keywords:
Keywords: MR-linac Unity output electronic portal imaging device daily check long-term stability
分类号:
R318；R811.1
DOI:
DOI:10.3969/j.issn.1005-202X.2021.11.009
文献标志码:
A
摘要:
目的：建立磁共振加速器Unity绝对剂量校准方法和输出量日检流程，并评价Unity输出量长期稳定性。方法：使用防水型指型电离室（PTW 30013）和特制的靴型水箱（Boot Phantom）进行绝对剂量校准，利用电子射野影像装置（EPID）图像确保模体摆位的准确性，选择适当的磁场修正因子修正磁场条件下电离室的响应。为节省时间，建立EPID图像特定像素点的累积灰度值与输出量的校准曲线，实现输出量日检。分析国家癌症中心/国家肿瘤临床医学研究中心/中国医学科学院北京协和医学院肿瘤医院放疗科新装的Unity从2019年10月22日至2020年5月9日的输出量日检结果，评估其输出量长期稳定性。结果：标准测量条件（SAD=143.5 cm，射野大小为10 cm×10 cm，机架角0°）下，水下10 cm处100 MU绝对剂量校准为0.87 Gy。在输出量变化±5%范围内，EPID像素点的累积灰度值与输出量高度线性相关（R2=0.999 9）。在116次Unity输出量日检中，输出量偏移基准值大于1%的仅有2次，并被标准测量方法证实。基于EPID的输出量日检方法相比标准输出量测量方法更方便快捷。结论：与常规加速器相比，Unity的绝对剂量校准更为复杂，需谨慎选择测量工具、摆位方式、测量条件和修正因子。初步结果显示，Unity具有较好的输出量长期稳定性；但真实临床工作负荷条件下，输出量长期稳定性还有待进一步观察。
Abstract:
Abstract: Objective To establish an absolute dose calibration method and determine daily output check process for Unity MR-linac (Unity), and to evaluate the output long-term stability of Unity. Methods A water-proof Farmer-type ion chamber (PTW 30013) and a specific water tank (boot phantom) were used for absolute dose calibration. The positioning accuracy of the phantom was ensured using electronic portal imaging device (EPID) images. An appropriate magnetic field correction factor was selected to correct the response of the ion chamber in magnetic field. In order to save time, a calibration curve of the accumulated pixel value and output for the specific pixels in EPID image was established for daily output check. The daily output of the Unity newly installed in Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College from October 22, 2019 to May 9, 2020 was analyzed for evaluating its output long-term stability. Results Under the standard measurement conditions (SAD=143.5 cm, field size=10 cm×10 cm, Gantry=0°), the absolute dose of 100 MU was calibrated to 0.87 Gy at 10 cm depth underwater. Within the routine range of daily output changes (±5%), the accumulated pixel value of the EPID pixel had highly linear correction with the output (R2=0.999 9). The output deviation from the reference value greater than 1% was only found in 2 daily output checks out of 116 daily output checks, and the results were confirmed by the standard method. The daily output check based on EPID was proved to be more convenient and faster than the standard method. Conclusion Compared with conventional accelerators, the absolute dose calibration of Unity is more complicated. It is necessary to choose the measurement tools, positioning methods, measurement conditions and correction factors carefully. Preliminary results show that Unity has a good output long-term stability, but it is needed to be further studied under real clinical workloads.

备注/Memo

备注/Memo:
【收稿日期】2021-05-03 【作者简介】田源，博士，副研究员，研究方向：放射物理，E-mail: tianyuan1981@hotmail.com 【通信作者】戴建荣，博士，研究员，研究方向：放射物理，E-mail: dai_jianrong@163.com
更新日期/Last Update: 2021-11-27