Journal of Medical Physics
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Year : 2019  |  Volume : 44  |  Issue : 4  |  Page : 231-238

Simple electronic portal imager-based pretreatment quality assurance using Acuros XB: A feasibility study

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

Correspondence Address:
Dr. Sureka Chandra Sekaran
Department of Medical Physics, Bharathiar University, Coimbatore - 641 046, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmp.JMP_84_19

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Objective: 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, FResultantand FTPSwere 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. Results: 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. Conclusion: 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.

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