Cumulative occupational exposure to low-dose radiation tied to higher cataract risk
It has long been known that relatively high-dose ionising radiation exposure (> 1 Gy) can induce cataract, but the radiogenic excess additive risk (EAR), arguably of more public health importance, has not been estimated. The researchers estimated EARs of cataract/cataract surgery in the USRT cohort using generalised additive models in relation to occupational radiation exposure, and assessed risk modification by a priori-selected cataract risk factors (diabetes, body mass index, smoking, race, sex, birth-year, ultraviolet B (UVB) radiation exposure).
They found that higher cumulative occupational exposure to low-dose radiation is associated with excess additive risk (EAR) of developing a cataract, according to findings of the study.
There were 11 345 cataract diagnoses and 5440 of cataract surgery during 832 462 and 888 402 person-years of follow-up, respectively.The researchers looked at a cohort of more than 63,352 radiation technologists with more than 832,000 person-years of follow up, including 11,345 with self-reported cataract. Radiation exposure was strongly associated with cataract, but not with cataract surgery.
The risk associated with radiation increased with age and was especially high among people 75 and older. Having diabetes was associated with a nearly 20-fold increase in the radiogenic EAR.
"Our findings, if confirmed, have important implications for clinical screening and public health along with consideration of radiation protection and regulatory measures, particularly for physicians performing fluoroscopically guided interventional procedures who have been shown to potentially receive eye-lens doses well over 100 mGy," Dr Mark P. Little of the National Cancer Institute in Bethesda, Maryland, and colleagues conclude.
High doses of radiation (1 Gy or more) can cause cataracts, and growing evidence suggests that cumulative lower doses (100-250 mGy) may induce cataracts as well, Dr Little and his team note in Occupational and Environmental Medicine.
To date, studies of radiation exposure and cataract have measured excess relative risk (ERR), the proportional increase in the risk of exposed vs. unexposed individuals. The authors used excess additive risk (EAR), which they say can more effectively gauge the public-health impact of radiation exposure "by providing an estimate of the number of cases that could potentially be prevented by reducing this exposure."
"Our study suggests that about five excess cases of cataract would be expected among 1,000 persons receiving 50 mGy (close to the mean level of exposure of 56 mGy in this cohort) and followed over 10 years (close to the mean 13.1-year follow-up). This suggests that special protective measures may be warranted for persons with diabetes who undergo radiation exposure," Dr Little and his team write.
"Future studies should assess EAR of cataracts along with ERRs in other radiation-exposed occupational groups with clinically ascertained diagnosis of cataract by cataract type, medical record validation of cataract severity/opacity, well-validated dosimetry and high-quality data on relevant life-style, environmental and medical risk factors, to ascertain if our findings are confirmed that cataract is inducible by low doses of radiation (at <100mGy)," they conclude.
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