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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

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.

Abstract

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, 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.

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.

KEYWORDS:

Electronic portal imaging device; portal dosimetry; pretreatment quality assurance

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