Abstract
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Introduction: The International Commission on Radiological Protection (ICRP) revised the threshold dose for the eye lens in 2012, leading to numerous studies focused on estimating eye lens doses for radiation workers. However, none of these studies have considered the cornea of the eye. It is important to note that the practical method of dosimetry for the eye lens introduces uncertainty. In this study, we developed a high-resolution pixelized phantom of the eye and utilized Monte Carlo simulation to estimate the doses to both the cornea and the lens. The primary objective of this study was to compare the doses to the cornea and the lens while investigating the impact of lead glasses on these tissues
Methods: In this study, the Monte Carlo toolkit named GATE (version 9.0, developed based on GEANT4 version 10.6) was employed to estimate the dose in the voxelized phantom of a typical human eye. Photon beams were generated using decay schemes of radionuclides (F-18, I-131, and Tc-99m) extracted from the MIRD book. We also considered these radionuclides inside the ICRP phantom and estimated the radiation emitted at the original radiation and spectra of emitted radiation from the phantom were the average energy of the photons. Lead glasses of different thicknesses (zero to 0.75 mm) were considered in front of the eye phantom separate Monte Carlo simulations.
Results: The ratio of corneal to lens doses for all radiations considered in this study was higher than unity. This ratio increased with increasing the thickness of lead glasses and also decreasing the average energy of radiation spectra. Due to increasing the lead glass thickness the ratio increased by 0.009, 0.014, and 0.034 for F-18, I-131, and Tc-99m respectively for their original radiation. However, the change in the ratio was not significant for F-18, I-131 but it was considerable for Tc-99m (0.031) for the radiation emitting from phantom at 3 m. However, the increased ratios were considerable due to a change in the average energy of spectra, 0.014, 0.021, and 0.024 for the three radionuclides tested respectively.
Conclusions: The corneal doses were higher for the radations from the three radionuclides tested. On average the corneal doses were higher by 12%, 11%, and 21% for t F-18, I-131, and Tc-99m respectively. Moreover, the calculation of standard deviation showed that the lens dose experiences a more pronounced variation compared to the cornea, at least for the three radionuclides tested in this study. With an increase in lead glasses' thickness, both lens and cornea doses decreased. However, the cornea-to-lens dose ratio rises, indicating a relatively greater reduction in lens dose.
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