Influence of eye lens dosimeter positioning in a realistic dosimetric phantom in reference radiation beams

Abstract

This paper presents a novel approach to dosimeter placement evaluation for personal eye lens dosimetry. A new assembly, known as the “Eye-Band”, and an anthropomorphic phantom containing two “Real Eye Dosimeters”, referred to as REDs, are proposed. The purpose of this study is to compare the energy and angular responses of the Eye-Band dosimeter assembly with those of an anthropomorphic dosimeter holder (RED-holder) placed inside a phantom. The objective is to analyze the maximum deviations between these measurements to determine the ideal placement of the holders from a metrological point of view. The commercially available BeOSL Eye Lens Dosimeters were also used for comparison, placed near each eye. BeO OSL EzClips were used as the sensitive elements in all three holders. Overall, except for 24 keV and 33 keV at 90° incidence, the differences between the dosimeters worn on the most exposed side of the head (Eye-Band or the standard commercial casings) and the estimated dose at the most exposed lens inside the anthropomorphic phantom were less than ∼20%. Results for the energy dependence of the central Eye-Band dosimeter at each angle of incidence (0°, 30°, 60° and 90°) showed that the deviation in dose to the most exposed eye (right eye) between RED and the central Eye-Band dosimeter ranged from 0% to ∼20% across all energies and angles from 0° to 90°. These results show that the angular dependence of the dosimeter on the most exposed side of the head is critical to ensure adequate results between the doses registered by the worn dosimeters at the side or center positions and the actual dose delivered to the most exposed eye. For the least exposed eye on the exit beam, the dosimeters worn on the left side (the left Eye-Band and the left standard commercial casing dosimeter worn near the left eye) are shown to be inadequate in representing the dose at the left eye position, even at a slight angle of incidence of 30°. This is due to partial shielding of the left dosimeters by the operator's head as the head rotates to the left. Anthropomorphic eye lens dosimeters have proven to be an invaluable tool for gaining a comprehensive understanding of the various factors influencing dose estimation in ocular lens dosimetry from a metrological perspective. This approach effectively bridges the gap between the controlled type testing conditions of dosimeters and real-world workplace conditions, while maintaining standard radiation beam conditions.