Output measurement of Unity MR-linac(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2021年第11期
- Page:
- 1365-1370
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Output measurement of Unity MR-linac
- 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
- Keywords:
- Keywords: MR-linac Unity output electronic portal imaging device daily check long-term stability
- PACS:
- R318；R811.1
- DOI:
- DOI:10.3969/j.issn.1005-202X.2021.11.009
- 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.
Last Update: 2021-11-27