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EPID-Based Three-Dimensional Dose Reconstruction Method

H Zheng*, J Zhao , M Cheng , J Jia , J Song , G Song , T He , Y Wu , Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; Anhui Radiotherapy Engineering Technology Research Center, Hefei, Anhui, 230031, China;


(Tuesday, 7/16/2019) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 3

Purpose: Three-dimensional dose verification can detect errors introduced by the treatment planning system (TPS) or differences between planned and delivered dose distribution during the treatment. This study mainly focuses on the dose reconstruction method based on electronic portal imaging device (EPID) back-projection.

Methods: The dose reconstruction method was based on the portal grey-value from EPID and the relationship between the beam through the phantom/body and grey-scoring voxels at the position of the EPID. Using thickness-dependence scatter kernels determined by series of experiments, the relationship was expressed in the form of grey response matrix which was quantified. Based on the grey response matrix, the two-dimensional incident fluence distribution would be reconstructed from the portal grey-value distribution information measured by the EPID. Based on the above studies, three-dimensional dose reconstruction model was designed and implemented in dose-guided real-time verification system KylinRay-DGRT with Visual C++. KylinRay-DGRT can guide physicists to adapt treatment plan to make sure accuracy of delivery dose in patient.

Results: KylinRay-DGRT was tested by C-Shape case in report of American association of physicists in medicine(AAPM) TG 119. The results showed that the reconstruction dose of KylinRay-DGRT is agreed with the measured dose, Gamma passing rates are more than 95.1%. KylinRay-DGRT was also applied in clinical head and neck case primarily. The results showed that the reconstruction dose of KylinRay-DGRT is agreed with the planned dose of reference TPS: Gamma passing rate at ISO transverse plane is 94.3%, 3D Gamma passing rate is 87.4%.

Conclusion: The results showed good satisfactions both on accuracy and speed for the clinical scenarios, laying great foundations for clinical implementation of dose guided radiotherapy. Some advanced functions, such as Monte Carlo pencil beam scatter kernels model, are under development.


Dosimetry, Reconstruction, Portal Imaging


TH- External beam- photons: portal dosimetry

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