Monte Carlo studies of the eyelid's influence on the absorbed dose in eye tissues

The aim of this work was to investigate the influence of the eyelid on the absorbed dose distribution in eye tissues. The study was performed using two versions of the female adult head phantom (FeH) connected to the GEANT4 Monte Carlo code: one has the eyes open and the second, closed. The calculations of organ dose, normalised to air KERMA free-in-air, were done for external exposures to photon radiation with energies between 10 and 200 keV. Three parallel beam sources were studied: anterior-posterior, left lateral and rotational. The doses between the two phantoms were compared with evident differences. The results show that for photon sources with energies lower than 30 keV, the attenuations by the eyelid are relevant in reducing the dose in the eye lens and cornea. This suggests that medical exposure protocols that use this energy range should consider advising patients to close their eyes during the exposure.