Enhancing Eye Dose Monitoring in Radiation Protection: Evaluating Hp(0.07) and OSLDs as an Alternative to Hp(3)

Background

Occupational exposure to ionizing radiation is a significant concern for medical workers, particularly those in interventional radiology and nuclear medicine. Radiation-induced cataract formation has led to stricter dose limits for the eye lens, as recommended by the International Commission on Radiological Protection (ICRP) [1]. Traditionally, Hp(3) has been the preferred metric for assessing eye dose, but due to limited availability of Hp(3) dosimeters, Hp(0.07) is often used as a surrogate [2].

While thermoluminescent dosimeters (TLDs) have been commonly used for eye dose monitoring, optically stimulated luminescent dosimeters (OSLDs) offer benefits such as higher sensitivity, reusability, and lower fading rates. This study evaluates the feasibility of using Hp(0.07) measured with OSLDs as an alternative for eye dose monitoring in radiation protection. Specifically, it aims to:

• Assess the correlation between Hp(0.07) and Hp(3) using OSLDs under controlled irradiation conditions.
• Evaluate OSLD dose accuracy relative to Monte Carlo (MC)-derived Hp(3) reference doses. ● Investigate the response of nanodot OSLDs to photon and beta radiation fields.
• Develop and test a prototype annealing system for OSLD reuse.
• Optimize annealing conditions for efficient dose resetting using different LED light sources.

Methods

This study builds upon the 2016 EURADOS report on eye lens dosimetry [3], using both photon and beta irradiations to evaluate nanodot and inlight OSLDs. Controlled irradiation experiments were conducted using custom 3D-printed PMMA eye phantoms, selected for their tissue-equivalent properties [4].

For photon irradiations, air kerma values were converted into Hp(3) equivalents using MC simulation-based conversion coefficients. OSLDs were exposed and their dose measurements were recorded using the MicroStar reader system. Accuracy was evaluated by comparing measured doses to expected Hp(3) values derived from air kerma-to-Hp(3) conversions.

For beta irradiations, standardized beta sources were used to examine OSLD response across different beta energy spectra. Dose response characteristics, including energy dependence and signal fading, were analyzed to determine the feasibility of nanodots for accurate eye lens dosimetry in mixed radiation fields [5].

An OSLD annealer was designed to reset irradiated nanodots for multiple measurement cycles. The annealer employed blue, green, and white LED light sources to optimize annealing conditions. Experimental trials assessed annealing efficiency by exposing nanodots to varying radiation doses and rereading dose levels at five-minute intervals using the MicroStar II system. The most effective light source was determined based on the time required to reduce stored dose levels below detectable limits [6].

Results

Preliminary results show a strong correlation between Hp(0.07) and Hp(3), confirming the feasibility of using Hp(0.07) as a surrogate for eye dose assessment. OSLD readings exhibited consistent performance across different radiation fields, with lower fading rates than traditional TLDs. The annealer successfully reset OSLDs, eliminating residual signals and ensuring accurate dose measurements across reuse cycles.

Blue LED light (470 nm) achieved the fastest annealing times, reducing doses below 8 Gy within 30 minutes and doses near 20 Gy within 55 minutes. White light required 40 minutes for doses under 8 Gy and 70 minutes for doses near 20 Gy. Green light was the least effective, requiring 90 and 140 minutes, respectively. These findings suggest that blue LED light is the most efficient annealing method for nanodot OSLDs, enhancing reusability and reducing measurement uncertainties.

Conclusion

This study demonstrates that Hp(0.07) can serve as a viable alternative to Hp(3) in eye dose assessments and highlights the advantages of OSLDs over conventional TLDs for radiation protection. Implementing an OSLD-based monitoring system, combined with an efficient annealing process, could improve the accuracy and efficiency of lens dose monitoring programs.

The development of a low-cost OSLD annealer further supports the feasibility of integrating nanodot OSLDs into routine monitoring. The use of blue LED light for annealing significantly reduces processing time, allowing for faster and more effective reuse of dosimeters. Future research should refine calibration methodologies, validate findings in real-world occupational settings, and explore the long-term effects of repeated annealing on OSLD sensitivity.

References

[1] ICRP, "ICRP Publication 118: Radiation Dose to the Lens of the Eye," 2012.

[2] R. Behrens and G. Dietze, "Personal dosimeters for eye lens dosimetry," Radiation Protection Dosimetry, vol. 139, no. 1-3, pp. 325-331, 2010.

[3] R. Behrens et al., "EURADOS Report 2016: Eye lens dosimetry," Radiation Protection Dosimetry, vol. 172, no. 1–3, pp. 21–28, 2016

[4] ICRU, "Tissue Substitutes in Radiation Dosimetry and Measurement," ICRU Report 44, 1989.

[5] S. Jang et al., "Characterization of OSLD response to beta radiation," Radiation Measurements, vol. 122, pp. 106190, 2019.

[6] J.-H. Kim et al., "Evaluation of blue LED light annealing in Al2O3:C for radiation dosimetry," Journal of Luminescence, vol. 138, pp. 147–153, 2013.