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Deterministic Effects to the Lens of the Eye Following Ionizing Radiation Exposure: is There Evidence to Support a Reduction in Threshold Dose?

Thome, Christopher*†; Chambers, Douglas, B.; Hooker, Antony, M.§; Thompson, Jeroen, W.**; Boreham, Douglas, R.*†**

doi: 10.1097/HP.0000000000000810
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Ionizing radiation exposure to the lens of the eye is a known cause of cataractogenesis. Historically, it was believed that the acute threshold dose for cataract formation was 5 Sv, and annual dose limits to the lens were set at 150 mSv. Recently, however, the International Commission on Radiological Protection has reduced their threshold dose estimate for deterministic effects to 0.5 Gy and is now recommending an occupational limit of 20 mSv per year on average. A number of organizations have questioned whether this new threshold and dose limit are justified based on the limited reliable data concerning radiation-induced cataracts. This review summarizes all of the published human epidemiological data on ionizing radiation exposure to the lens of the eye in order to evaluate the proposed threshold. Data from a variety of exposure cohorts are reviewed, including atomic bomb survivors, Chernobyl liquidators, medical workers, and radiotherapy patients. Overall, there is not conclusive evidence that the threshold dose for cataract formation should be reduced to 0.5 Gy. Many of the studies reviewed here are challenging to incorporate into an overall risk model due to inconsistencies with dosimetry, sample size, and scoring metrics. Additionally, risk levels in the studied cohorts may not relate to occupational scenarios due to differences in dose rate, radiation quality, age at exposure and latency period. New studies should be designed specifically focused on occupational exposures, with reliable dosimetry and grading methods for lens opacities, to determine an appropriate level for dose threshold and exposure limit.

*Northern Ontario School of Medicine, 935 Ramsey Lake Road, Sudbury, Ontario, Canada, P3E 2C6; † Laurentian University, 935 Ramsey Lake Road, Sudbury, Ontario, Canada, P3E 2C6; ‡ Arcadis, 121 Granton Drive Suite 12, Richmond Hill, Ontario, Canada, L4B 3N4; § Flinders University School of Medicine, GPO Box 2100, Bedford Park, South Australia, Australia, 5001; ** Bruce Power, 177 Tie Road, R.R.2, Tiverton, Ontario, Canada, N0G 2T0.

The authors declare no conflicts of interest.

For correspondence contact: Christopher Thome, Northern Ontario School of Medicine, 935 Ramsey Lake Road, Sudbury, Ontario, P3E 2C6, or email at cthome@nosm.ca.

(Manuscript accepted 5 July 2017)

© 2018 by the Health Physics Society