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J Med Phys. 2019 Oct-Dec;44(4):231-238. doi: 10.4103/jmp.JMP_84_19. Epub 2019 Dec 11.

Simple Electronic Portal Imager-Based Pretreatment Quality Assurance using Acuros XB: A Feasibility Study.

Author information

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India.
Department of Radiation Oncology, Fortis Memorial Research Institute, Gurgaon, India.
Department of Radiotherapy, Government General Hospital, Guntur, Andhra Pradesh, India.



This study demonstrates a novel electronic portal imaging device (EPID)-based forward dosimetry approach for pretreatment quality assurance aided by a treatment planning system (TPS).

Materials and Methods:

Dynamic multileaf collimator intensity-modulated radiation therapy (IMRT) plans were delivered in EPID and fluence was captured on a beam-by-beam basis (FEPID). An open field having dimensions equal to those of the largest IMRT field was used in the TPS to obtain the transmitted fluence. This represented the patient-specific heterogeneity correction (Fhet). To obtain the resultant heterogeneity-corrected fluence, EPID measured fluence was corrected for the TPS generated heterogeneity (FResultant = FEPID × Fhet). Next, the calculated fluence per beam basis was collected from TPS (FTPS). Finally, FResultant and FTPS were compared using a 3% percentage dose difference (% DD)-3 mm distance to agreement [DTA] gamma analysis in an isocentric plane (two-dimensional [2D]) and multiple planes (quasi three-dimensional [3D]) orthogonal to the beam axis.


The 2D heterogeneity-corrected dose reconstruction revealed a mean γ passing of the pelvis, thorax, and head-and-neck cases of 96.3% ±2.0%, 96.3% ±1.8%, and 96.1% ±2.2%, respectively. Quasi-3D γ passing for the pelvis, thorax, and head-and-neck cases were 97.5% ±1.4%, 96.3% ±2.4%, and 97.5% ±1.0%, respectively.


EPID dosimetry produced an inferior result due to no heterogeneity corrections for sites such as the lung and esophagus. Incorporating TPS-based heterogeneity correction improved the EPID dosimetry result for those sites with large heterogeneity.


Electronic portal imaging device; portal dosimetry; pretreatment quality assurance

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