Nuclear Science and Techniques

《核技术》(英文版) ISSN 1001-8042 CN 31-1559/TL     2019 Impact factor 1.556

Nuclear Science and Techniques ›› 2015, Vol. 26 ›› Issue (5): 050201 doi: 10.13538/j.1001-8042/nst.26.050201

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A method for direct conversion of EPID images to incident fluence for dose reconstruction

REN Qiang,1, 2, 3, 4 CAO Rui-Fen,2, 3, 4 PEI Xi,2, 3, 4 LI Bing-Bing,5 HU Li-Qin,1, 2, 3, 4 WU Yi-Can 1, 2, 3, 4   

  1. 1University of Science and Technology of China, Hefei 230027, China
    2Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei 230031, China 3Anhui Radiotherapy Engineering Technology Research Center, Hefei 230031, China
    4Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Suzhou 215006, China
    5Radiotherapy center, Cancer Hospital, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
  • Contact: HU Li-Qin E-mail:liqin.hu@fds.org.cn
  • Supported by:

    Supported by National Natural Science Foundation of China (No. 81101132) and Natural Science Foundation of Anhui Province (No. 11040606Q55)

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REN Qiang, CAO Rui-Fen, PEI Xi, LI Bing-Bing, HU Li-Qin, WU Yi-Can . A method for direct conversion of EPID images to incident fluence for dose reconstruction.Nuclear Science and Techniques, 2015, 26(5): 050201     doi: 10.13538/j.1001-8042/nst.26.050201

Abstract:

A direct incident fluence measurement method based on amorphous silicon electronic portal imaging device (a-Si EPID) has been developed for pretreatment verification of intensity-modulated radiation therapy (IMRT). The EPID-based incident fluence conversion method deconvolves EPID images to the primary response distribution based on measured lateral scatter kernels in the EPID detector using Conjugate Gradient algorithm. The primary response is converted to the incident fluence based on measured fluence conversion matrix which corrects for off-axis position dependence of the a-Si EPID response and the “horn” beam profile caused by flatting filter. To verify feasibility and accuracy of this method, square fields of various sizes and two IMRT plans were delivered. The dose distributions computed based on EPID-derived incident fluence were compared with the measurement data. For all square field sizes except the smallest field (2 cm), the mean dose differences in cross-line dose profiles were within 1% excluding the penumbra region, and gamma passing percentages with a 2%/2mm criterion were about 99%. For two IMRT plans, the least gamma passing percentage for all eight IMRT fields was 98.14% with 2%/3mm criteria. It can be concluded that our direct EPID-based incident fluence conversion method is accurate and capable of being applied to pretreatment dose verification in clinical routines.

Key words: Amorphous-silicon portal imaging devices, Dose reconstruction, Dose verification