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Monte Carlo Simulations of EPID Transit Dosimetry: A Feasibility Study

L Yu*, J Wang , W Hu , X Xia , Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China


(Monday, 7/15/2019) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 1

Purpose: To investigate the feasibility of patient-onboard portal dose quality assurance (QA) for IMRT plans based on Monte Carlo (MC) simulations.

Methods: We performed MC simulations on a voxelised EPID model (Varian aS1000) using the Geant4-based Architecture for Medicine-Oriented Simulations (GAMOS, version 6.0.0). The EPID positioned under a phantom was irradiated and the deposited dose in each voxel was calculated to acquire a portal image. A 60-pair multileaf collimator (MLC) was modelled in the simulations to form a conformal field. To reproduce the beam information as realistic as possible, the phase-space data above the MLC of Varian Clinac iX provided by IAEA was used.

Results: The percentage depth dose (PDD) and lateral dose profiles were firstly examined and the simulated results showed a good agreement with the measurements. We also compared the portal image of a 10cm x 10cm field and a gamma passing rate of 100% was achieved.

Conclusion: The MC simulation results on phantom suggest that a proper model of linac and EPID detector has been established and it is possible to perform patient-onboard portal dose QA.


Monte Carlo, Portal Imaging, Transit Dosimetry


TH- External beam- photons: portal dosimetry

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