Monitoring the eye lens

Purpose To prevent the induction of cataracts by ionizing radiation (photons or betas), the International Commission on Radiological Protection (ICRP) has lowered the annual dose limit for the eye lens from 150 mSv down to 20 mSv for occupational exposures. Thus, protecting the eye and monitoring the lens dose to prevent exceeding the dose limit is more necessary than formerly assumed. Methods Different kinds of dosemeters were investigated to give guidelines on monitoring the lens dose when necessary. Results Hp(0.07) dosemeters are constructed to monitor the local skin dose in 0.07 mm depth as the radiation‐sensitive epidermis lies about 0.07 mm below the surface. In pure photon radiation fields, e.g. in interventional radiology, Hp(0.07) dosemeters are appropriate to monitor the lens dose when worn near the eye and if the back of their case consists of thin plastic. In beta radiation fields, e.g. in nuclear medicine, Hp(0.07) dosemeters may overestimate the lens dose by a factor of 100 or more. Thus, they are unsuitable here. Hp(3) dosemeters are constructed to monitor the lens dose as the radiation‐sensitive part of the lens lies about 3 mm within the eye. Only very few Hp(3) dosemeters exist, but, by construction, they should monitor the lens dose also in beta fields correctly. However, this has not yet been demonstrated. Hp(10) dosemeters are constructed to monitor the whole body dose as the inner organs are assumed to lie about 10 mm within the trunk. Hp(10) dosemeters usually underestimate the lens dose and are, thus, unsuitable. Conclusion Protection measures such as lead glass shields or glasses should be used. In case exposures cannot be avoided, appropriate dosemeters must be worn near the eye behind devices used to shield the eyes but not behind a shield worn on the trunk (e.g. a lead apron).