Prog Med Phys.  2024 Sep;35(3):59-66. 10.14316/pmp.2024.35.3.59.

Development of a Flexible Eye Shield Phantom for Artifact-Free Computed Tomography Images

• Kang S
• Choi CH
• Kim Ji
• Yu GB
• Cho JD

• KMID: 2559976
• DOI: http://doi.org/10.14316/pmp.2024.35.3.59

Abstract

Purpose
This study aimed to develop a flexible eye shield phantom to acquire artifact-free computed tomography (CT) images for electron beam radiotherapy.
Methods
A flexible eye shield phantom for a newly designed eye shield was fabricated. Because of metal artifacts caused by an eye shield composed of high-density materials such as tungsten or lead, CT image acquisition is not appropriate for treatment planning because of inaccurate dose calculation and organ-at-risk delineation. To acquire artifact-free CT images, a mold of the same size as the outer dimension of the metallic eye shield was manufactured using 3D printing. The flexible eye shield phantom was imaged using a Philips Brilliance CT Big Bore under the same condition as the measurement. The phantom image with an average of 200 Hounsfield unit (HU) was imported into the treatment planning systems (TPS) and assigned a value of 26,750 HU to consider the material density of tungsten. The dosimetric comparison using a 6-MeV electron beam was performed. Measurement was performed using a metal oxide semiconductor field effect transistor detector for point doses at 3 and 10 mm.
Results
The artifact-free CT images using a flexible eye shield phantom without air bubbles were transferred into the TPS. The dose at 10 mm calculated using the TPS agreed with the ionchamber measurements within 2 cGy. Conversely, a larger dose discrepancy between the measured and calculated doses was found at 3 mm depth.
Conclusions
The flexible eye shield phantom was successfully fabricated to apply electron treatment planning by acquiring artifact-free CT images. The dose calculated using the artifact-free image was comparable to the measured dose at lens depth when applying an eye shield.

Keyword

Eye shielding; Flexible eye shield phantom; Artifact-free CT image

Figure

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  Fig. 1 Newly designed eye shield (small, medium, and large).

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  Fig. 2 Fabrication process of the flexible eye shield phantom.

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  Fig. 3 Setup of the transmission and backscatter measurement of the eye shield. SSD, source-to-surface distance; Al, aluminium.

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  Fig. 4 Fabricated flexible eye shield phantom.

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  Fig. 5 Dose distribution calculated using the density override for the flexible eye shield phantom and tungsten eye shield.

Reference

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