The effects of simulating a realistic eye model on the eye dose of an adult male undergoing head computed tomography

Investigation of the effect of using radiation protective glasses on the photon fluence-to-dose conversion coefficients of eye substructures

The use of radiation protective glasses is common in radiation-contaminated environments. However, the effect of these glasses has not yet been investigated on the fluence-to-dose conversion coefficients (DCCs). The aim of this study is to investigate the effect of five types of gamma ray protective glasses on the photon fluence-to-DCCs of different eye substructures. For this purpose, a real eye model has been used and its conversion coefficients have been calculated in the presence of five types eye protective glasses with chemical formulae of ZnO-PbO-B₂O₃, Bi₂O₃-PbO-B₂O₃, PbO-B₂O₃, PbO-BaO-Na₂O-MgO-B₂O₃and BaO-Nb₂O₃-P₂O₅. Calculations were performed for monoenergetic photon sources, whose energy ranges from 0.02 to 10 MeV, with different polar and azimuthal angles. The results indicate that the use of radiation protective glasses has acceptable effects on reducing the fluence-to-DCCs only at low photon energies up to 500 keV. At medium energy levels up to about 1 MeV, the effect of the glasses is negligible. However, at high energies it increases the fluence-to-DCCs for sensitive parts of the eye.

Dosimetric comparison between realistic ocular model and other models for COMS plaque brachytherapy with 103Pd, 131Cs, and 125I radioisotopes

Nowadays, Monte Carlo calculations are commonly used for the evaluation of dose distributions and dose volume histograms in eye brachytherapy. However, currently available eye models have simple geometries, and main substructures of the eye are either not defined in details or not distinguished at all. In this work absorbed doses of eye substructures have been estimated for eye plaque brachytherapy using the most realistic eye model available, and compared with absorbed doses obtained with other available eye models. For this, a medium-sized tumour on the left sides of the right eye was considered. Dosimetry calculations were performed for four different eye models developed based on a literature review, and using a 12 mm Collaborative Ocular Melanoma Study plaque containing ¹³¹Cs, ¹⁰³Pd, and ¹²⁵I sources. Obtained results illustrate that the estimated doses received by different eye substructures strongly depend on the model used to represent the eye. It is shown here that using a non-realistic eye model leads to a wrong estimation of doses for some eye substructures. For example, dose differences of up to 35% were observed between the models proposed by Nogueira and co-workers and Yoriyaz and co-workers, while doses obtained by use of the models proposed by Lesperance and co-workers, and Behrens and co-workers differed up to 100 and 63% as compared to the situation when a realistic model was used, respectively. Moreover, comparing different radionuclides showed that the most uniform dose distribution in the considered tumour region was that from ¹³¹Cs, with a coefficient of variation of 33%. In addition, considering the realistic eye model, it was found that the radiosensitive region of the lens received more than the threshold dose of cataract induction (0.5 Gy), for all investigated radionuclides.