Proposal for a new operational quantity for eye lens photon dosimetry

In the past, little attention was given to measuring the radiation dose received by the lens of the eye. It was assumed that limiting the total body dose to 20 mSv per year provided adequate protection for the lens in all practical workplace situations. However, after the International Commission on Radiological Protection (ICRP) issued a statement proposing to reduce the limit for occupational exposure from 150 to 20 mSv per year, the importance of eye-lens photon dosimetry increased. This work proposes a new operational quantity D(6)water as an alternative to Hp (3) for evaluating the dose received by the lens of the eye. The proposed quantity is a physical one, which means it can be measured directly. Fluence-to-D(6)water conversion coefficients are calculated for photon energies ranging from 0.02 to 10 MeV using the Monte Carlo transport code EGSnrc without resorting to the kerma approximation, meaning a more accurate and realistic radiation dose assessment. Comparison of the conversion coefficients with those of the absorbed dose to the lens of the eye (Dlens), published by the ICRP shows that D(6)water can adequately represent Dlens over the entire considered energy range.