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Investigation of the use of external aluminium targets for portal imaging in a medical accelerator using Geant4 Monte Carlo simulation

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Author(s)
Hyungdong KimByungyong KimJonggeun BaekYoungkee OhSangmo YunHyunsoo Jang
Keimyung Author(s)
Oh, Young Kee
Department
Dept. of Radiation Oncology (방사선종양학)
Journal Title
British Journal of Radiology
Issued Date
2018
Volume
91
Issue
1084
Abstract
OBJECTIVE:

To install a low-Z target on the wedge tray mount of a medical linear accelerator to create a new image beam and to confirm image contrast enhancement.

METHODS:

Experimental low-energy photon beams were produced with the linac running in the 6 MeV electron mode and with a low-Z target installed on the wedge tray mount [denoted 6 MeV (low-Z target)]. Geant4 Monte Carlo simulation was performed to analyse the energy spectrum and image contrast of a 6 MeV (low-Z target) beam. This study modelled the 6 MeV (low-Z target) beam and the 6 MV (megavoltage) radiotherapy photon beam and verified model validity by measurement. In addition, a contrast phantom was modelled to quantitatively compare the image contrasts of the 6 MeV (low-Z target) beam and the 6 MV radiotherapy photon beam. A low-Z target was fabricated to generate low-energy photons (25-150 keV) from incident electrons, and a portal image of the Alderson RANDO phantom was acquired using a clinical linear accelerator for qualitative analysis.

RESULTS:

The measured and calculated percentage depth dose of the 6 MV photon and 6 MeV (Al) beams were consistent within 1.5 and 1.6%, respectively, and calculated lateral profiles of the 6 MV photon beam and the 6 MeV (Al) beam were consistent with the measured results within 1.5 and 1.9%, respectively. Although low-energy photons (25-150 keV) of the 6 MV photon beam were only 0.3%, the Be, C, and Al low-Z targets, but not the Ti target, generated 34.4 to 38.5% low-energy photons. In 5 to 20 cm water phantoms, contrast of the 6 MeV (Al) beam was approximately 1.16 times greater than that of the 6 MV beam. The contrasts of 6 MeV (Al) and 6 MV photon beams in the 20 cm water phantom were ~34% lower than those in the 5 cm water phantom. 6 MeV (Al)/CR (computed radiography) images of the human body phantom were more vivid and detailed than 6 MV/EPID (electronic portal imaging device) and 6 MeV (Al)/EPID images.

CONCLUSION:

The experimental beam with a low-Z target, which was simply installed on the wedge tray mount of the radiotherapy linear accelerator, generated significantly more low-energy photons than the 6 MV radiotherapy photon beam, and provided better quality portal images. Advances in knowledge: This study shows that, unlike the existing low-Z beam studies, a low-Z target can be installed outside the head of a linear accelerator to improve portal image quality.
Keimyung Author(s)(Kor)
오영기
Publisher
School of Medicine (의과대학)
Citation
Hyungdong Kim et al. (2018). Investigation of the use of external aluminium targets for portal imaging in a medical accelerator using Geant4 Monte Carlo simulation. British Journal of Radiology, 91(1084), 2017037–2017037. doi: 10.1259/bjr.20170376
Type
Article
ISSN
0007-1285
Source
https://www.birpublications.org/doi/10.1259/bjr.20170376
DOI
10.1259/bjr.20170376
URI
https://kumel.medlib.dsmc.or.kr/handle/2015.oak/41321
Appears in Collections:
1. School of Medicine (의과대학) > Dept. of Radiation Oncology (방사선종양학)
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