European epidemiological study on radiation-induced lens opacities for interventional cardiologists

The aim of the EURALOC project was to evaluate dose-response relations for the development of radiation induced postcapsular eye lens opacities and cataracts in a cohort interventional cardiologist with relatively high exposure. Traditionally, cataracts has been considered as a deterministic effect, with threshold doses of 1-2 Gy, which had to be exceeded to develop opacities or cataracts. Below this level it has been considered that there was no risk. However, in the last 10 years there have been several studies having detected lens opacities at levels below the previously assumed threshold of 1-2 Gy. Important contributions have been re-analysis of data for the Japanese nuclear bomb victims and a study on rescue and cleanup workers in Chernobyl. With background in these studies, the International Commission on Radiological Protection (ICRP) revised its recommendation on the occupational dose limit for eye lens, from 150 mSv per year to 20 mSv per year. Some studies have also looked at the risk of occupationally exposed personnel with low-dose radiation. This have been volunteering interventional cardiologists and radiologists, nurses and radiographers at conferences, which been compared to an unexposed group. These studies have suggested an increased risk of lens opacities, mainly postsubcapsular (PSC) lens opacities. However, these studies have only focused on comparing an exposed group with an unexposed group, and has not provided any information about dose-response relations. Previous studies have studied the prevalence of lens opacities among cardiologists and radiologists. In a French study of 106 interventional cardiologists and 99 unexposed persons in a control group, an increased risk of PSC lens opacities was found (17% versus 5%). These findings have led to the question whether radiation induced lens opacities are a deterministic effect, or if it may have a more stochastic nature, i.e. a small increase of the risk may also occur with small radiation doses to the eye lens. In the EURALOC project, 393 interventional cardiologists was recruited and 294 unexposed persons in the eleven countries that participated in the study. A joint protocol were developed, which included two questionnaires. One about occupational history that asked about the number of years of interventional cardiology, type of procedures and number of them, type of equipment and various radiation protection devices that been used for different 10-year periods. The second questionnaire was about personal medical history with questions about, among other things, potential predisposing factors for lens opacities and cataracts. All recruited persons underwent a slit lamp survey, evaluated with LOCSIII classification. There were also Scheimpflug investigations of 238 recruited persons (cardiologists + control group). All images were reviewed by ophthalmologists locally and also ophthalmologists participating in the project. Retrospective analyzes have been conducted of cumulative eye lens dose, taking into account the eye lens dose per exposure configuration (type of procedure, type of X-ray device and type of protection) along with individual occupational history information. Analyzes of images from the ophthalmological survey showed a significantly more frequent occurrence of PSC lens opacities in cardiologists, relative to the unexposed control group. A linear, non-threshold, dose-response relation for the development of PSC opacities were found. A cardiologist with a cumulative lens dose of 1 Gy to the eye lens will have a 2.31 times greater chance of developing PSC lens opacities, compared to an unexposed person of the same age and status of both eyes. Age were found to be the factor that mainly affects the development of PSC lens opacities and with a possible borderline involvement of diabetes mellitus. It was not possible to find support for tobacco smoking, gender, body mass index, hypertension or hypercholesterolemia for increased risk of PSC lens opacities. Two different tools were developed with two different functions. The mobile app mEyeDose is aimed for interventional cardiologists. In mEyeDose, the cardiologist can follow and learn more about his own eye lens dose, based on workload and protective measures (ceiling mounted shielding, protective goggles etc.). By changing the various protection measures, one can see how different optimization measures will affect the radiation dose to the eye lens. The lens dose may be displayed for a selected time period or as a total cumulative dose. The desktop software mEyeDose_X is more aimed at radiation protection officers, physicists and others who work with radiation protection. It can be used to follow, optimize and calculate eye lens doses for cardiologists, based on workload, type of procedures and/or personal dosimeter readings over the apron.

The proposed research, called EURALOC, focuses on low dose radiation effects on the lens of the eye. Research on formation of lens opacities following radiation exposure has been an area of intense interest recently and is a major target area of the MELODI Strategic Research Agenda. Several issues regarding the relationship between radiation dose, lens opacities and cataract development remain unclear and there is an urgent need for high-quality epidemiological studies at low doses. EURALOC will combine epidemiological, ophthalmological and dosimetric research expertise to address effects of radiation on the lens of the eye and to determine the dose-response relationship at low doses. A well-designed epidemiological study on a European cohort of interventional cardiologists with cutting edge methods for evaluating opacities and eye lens dosimetry is planned. The strengths of our EURALOC consortium is the methodology to guarantee harmonised data collection, the availability of state of the art dosimetry methods and of standardised, central ophthalmological assessments, including non-invasive, quantitative measure of lens transparency developed earlier in the ELDO project. The reduction of the occupational dose limit for the eye lens to 20 mSv per yearwill have implications for the targeted population in this study and for other health care professionals, as previous studies have shown that this limit can easily be exceeded for medical staff. A clarification of the dose-response relationship for radiation-induced lens opacities will not only provide a scientific basis for the determination of the low-dose threshold for lens opacities, but will also have an impact on the improvement of radiation protection and dose reduction procedures for medical staff in the clinical environment.