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Radiation to the eye: which dosemeter to use?

Especially interesting for
  • manufacturers of dosemeters
  • medical staff

The International Commission on Radiological Protection (ICRP) has drastically lowered its recommended annual dose limit for the eye lens. Detailed calculations made at PTB have shown which kinds of dosemeters are suited to monitor the dose received by the eye lens.

Stylized model of the eye (including details in the inner part of the lens) as was used for the high-precision dose calculations. The different colours represent different materials. The right part of the image shows the full skull model including the inserted eye.

The human eye is even more sensitive to ionizing radiation than previously assumed. There is mounting evidence that the dose limit currently valid does not suffice to prevent cataract. For this reason, the International Commission on Radiological Protection (ICRP) has drastically lowered its recommended dose limit for the eye lens, namely from 150 millisievert (mSv) to 20 mSv per year. With the previous dose limit, one supposed that it was sufficient to monitor the values for the whole body (by means of whole-body dosemeters) and for the skin (with skin dosemeters) as a routine. Should the dose limit for the eye lens be lowered also in Germany, this could imply that suitable dosemeters must be worn in the direct vicinity of the eye behind appropriate eye protection. Staff members who have attained their maximum annual dose may then no longer be employed in a radiation controlled area for the rest of the year.

With the aid of Monte Carlo simulations, PTB has performed dose de t e rmi nat ion specifically for the eye lens and then examined the different kinds of dosemeters as to their applicability in this precise case. It turned out that skin dosemeters are suited, however, for Xrays only (e. g. in radiology). They have to be worn in the direct vicinity of the eye, and they have to be permeable to X-rays at the back. For beta radiation – which often occurs in nuclear medicine – skin dosemeters might overestimate the actual dose by a factor of 100 or more and are therefore not suited. Eye dosemeters – which estimate the dose in the part of the eye lens that is particularly sensitive to radiation – are fundamentally suited. However, only very few types of this kind of dosemeter exist, as the measurand has so far not been used. Their fitness for purpose in the case of beta radiation is still to be tested. Whole-body dosemeters are categorically not suitable as they underestimate the radiation dose to the eye lens, especially in the case of beta radiation and of low-energy X-rays.

PTB’s results, with the support of the BMWi project “Innovation with Standards – INS: Improved monitoring of the eye lens dose”, are to be transposed into national and international standards.


Rolf Behrens,
Department 6.3 Radiation protection dosimetry
phone: +49 (0) 531 592-6340
e-mail: rolf.behrens(at)ptb.de