open access

Vol 24, No 6 (2019)
Original research articles
Published online: 2019-11-01
Submitted: 2019-05-02
Get Citation

Set-up error validation with EPID images: Measurements vs Egs_cbct simulation

D. van Eeden, F.H.J. O’Reilly, F.C.P. du Plessis
DOI: 10.1016/j.rpor.2019.09.013
·
Rep Pract Oncol Radiother 2019;24(6):614-623.

open access

Vol 24, No 6 (2019)
Original research articles
Published online: 2019-11-01
Submitted: 2019-05-02

Abstract

Aim

In this study, the egs_cbct code’s ability to replicate an electronic portal imaging device (EPID) is explored.

Background

We have investigated head and neck (H&N) setup verification on an Elekta Precise linear accelerator. It is equipped with an electronic portal imaging device (EPID) that can capture a set of projection images over different gantry angles.

Methods and materials

Cone-beam computed tomography (CBCT) images were reconstructed from projection images of two different setup scenarios. Projections of an Anthropomorphic Rando head phantom were also simulated by using the egs_cbct Monte Carlo code for comparison with the measured projections.

Afterwards, CBCT images were reconstructed from this data. Image quality was evaluated against a metric defined as the image acquisition interval (IAI). It determines the number of projection images to be used for CBCT image reconstruction.

Results

From this results it was established that phantom shifts could be determined within 2 mm and rotations within one degree accuracy using only 20 projection images (IAI = 10 degrees). Similar results were obtained with the simulated data.

Conclusion

In this study it is demonstrated that a head and neck setup can be verified using substantially fewer projection images. Bony landmarks and air cavities could still be observed in the reconstructed Rando head phantom. The egs_cbct code can be used as a tool to investigate setup errors without tedious measurements with an EPID system.

Abstract

Aim

In this study, the egs_cbct code’s ability to replicate an electronic portal imaging device (EPID) is explored.

Background

We have investigated head and neck (H&N) setup verification on an Elekta Precise linear accelerator. It is equipped with an electronic portal imaging device (EPID) that can capture a set of projection images over different gantry angles.

Methods and materials

Cone-beam computed tomography (CBCT) images were reconstructed from projection images of two different setup scenarios. Projections of an Anthropomorphic Rando head phantom were also simulated by using the egs_cbct Monte Carlo code for comparison with the measured projections.

Afterwards, CBCT images were reconstructed from this data. Image quality was evaluated against a metric defined as the image acquisition interval (IAI). It determines the number of projection images to be used for CBCT image reconstruction.

Results

From this results it was established that phantom shifts could be determined within 2 mm and rotations within one degree accuracy using only 20 projection images (IAI = 10 degrees). Similar results were obtained with the simulated data.

Conclusion

In this study it is demonstrated that a head and neck setup can be verified using substantially fewer projection images. Bony landmarks and air cavities could still be observed in the reconstructed Rando head phantom. The egs_cbct code can be used as a tool to investigate setup errors without tedious measurements with an EPID system.

Get Citation

Keywords

Cone-beam CT; EPID; Image acquisition interval; Monte Carlo; egs_cbct

About this article
Title

Set-up error validation with EPID images: Measurements vs Egs_cbct simulation

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 24, No 6 (2019)

Pages

614-623

Published online

2019-11-01

DOI

10.1016/j.rpor.2019.09.013

Bibliographic record

Rep Pract Oncol Radiother 2019;24(6):614-623.

Keywords

Cone-beam CT
EPID
Image acquisition interval
Monte Carlo
egs_cbct

Authors

D. van Eeden
F.H.J. O’Reilly
F.C.P. du Plessis

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