New Findings Reveal: Higher Radiation Protection Needed due to Reduction in Occupational Radiation Dose Limit to the Lens of the Eye
The ICRP has lowered the absorbed radiation dose to the lens of the eye significantly. This means for many radiation users that the new radiation dose limit could be reached across their working life.
Reduced Radiation Dose Limit to the Lens of the Eye
In April 2011, the ICRP (International Commission on Radiology Protection; an independent, international, non-governmental organisation which provide recommendations and guidance on radiological protection concerning ionising radiation) released an official communication titled ‘Statement on Tissue Reactions’ which pointed to new epidemiological evidence relating to the tissue reaction effects of doses to the lens of the human eye. As a result, “the Commission now recommends an equivalent dose limit for the lens of the eye of 20 mSv in a year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv.” (1)
Based on this recent evidence, the ICRP now defined a new threshold value for tissue reactions to be an absorbed dose of 0.5 Gy to the lens of the eye, which is almost a tenfold reduction as compared to the previous value of 5 Gy given by the ICRP. This means for many employees of Australia’s medical workforce, who are exposed to radiation, that the new dose limit could reasonably be reached across their working life.
Health Concerns of Radiation Exposure to the Eye
Since this crucial new evidence, the biggest concern is the development of cataracts, which are usually a result of long-term exposure to low-dose radiation and continuous high exposure that can even lead to blindness.
Workplaces and medical staff still seem to underestimate the health risks to their eyes. According to the study “Historical review of occupational exposures and cancer risks in medical radiation workers” (2) 50% of interventional cardiologists develop cataracts. The risk of cataracts rises as the amount of exposure rises, e.g. during interventional radiology procedures, which are mainly:
- Computed Tomography (CT) and CT fluoroscopy
Health professionals that are at risk of radiation induced eye lens injury
Mainly interventional cardiologists and interventional radiologists are of the highest risk. However, doctors and nurses using fluoroscopy in operating theatres, e.g. orthopaedic surgeons, urologists, gastroenterologists, anaethesists may also be at risk. Furthermore, paramedics who stay close to the patient during the procedure. These workers may be within a high-scatter X-ray field for several hours a day during procedures. The risk for eye lens injuries is particularly increased for high workloads unless suitable protective tools and proper operational measures are used.
Implications for Medical Staff Exposed to Radiation
Workplaces and medical staff are encouraged to adopt changes in advance of regulatory change to avoid or minimise health risks. Unfortunately regulatory change often lags behind and can take years to be implemented across Australia.
Since the ICRP officially alerted a predominant decrease in the advised levels of the occupation dose limit to the lens of the eye, the RHC (Radiation Health Committee, an advisory board to the Australian Radiation Protection and Nuclear Safety Agency) have instigated an awareness process that have alerted those professionals, who are susceptible to frequent radiation exposure (such as interventional radiologists and cardiologists, vascular and orthopaedic surgeons), of the decrease in dose limit to the eye (3).
The RCH strongly recommended that work places and radiation users should be:
- Educated in the importance of the changes and thus encouraged to ensure adequate protection procedures are consistently implemented for relevant staff.
- Assessed the potential eye dose levels of affected medical staff during procedures using radiation.
- Advised by the hospital’s radiation safety officers and/ or medical physicists of any measures required that address the revised reduction in recommended radiation dose levels as a commitment to protecting their staff.
Furthermore, RCH advised that the new limit is to be incorporated in the Radiation Protection Guidelines & Policies of all work places in Australia. This would imply immediate action is needed to avoid health risks to medical workers.
Some Measures to Minimise Radiation Exposure to the Eyes and the Body Are:
1. Use personal radiation protection equipment.
Performing a few fluoroscopic procedures per week that require only a few minutes of fluoroscopy time per procedure (i.e. less than 5 minutes), sufficient protection of the eye lens can be achieved by using a lead screen or wearing Radiation Safety Eyewear, also called lead glasses or x-ray glasses. Lead screens and lead glasses come in different radiation safety protection levels and provide the most effective radiation protection for your eyes if they are worn/ used during any interventional radiology procedures.
For long fluoroscopy procedures (i.e. more than 10 minutes per procedure) and many procedures per day, such as in busy interventional cardiology or interventional radiology suites, there is a substantial risk of lens opacity. However, even in these situations, if medical staff use effective radiation protection for the eye, the probability of cataract can be reduced.
2. Consider where you stand in relation to the X-ray tube during a fluoroscopic procedure.
The scattered radiation from the patient comprises the main source of radiation dose to staff. Measurements have shown that scattered radiation from a patient’s body is more intense at the entrance side of X-ray beam, i.e. on the side where the X-ray tube is located. Therefore, it is better to stand on the exit side of the detector, and not on the X-ray tube side during a fluoroscopic procedure. Typically, only around 1% to 5 % of the radiation falling on the patient body comes out on the exit side. So, if you stand on the side of transmitted beam you encounter scattered radiation corresponding to only 1% to 5% of the incident beam intensity, whereas you encounter scattered radiation corresponding to 100% of the entrance beam intensity on other side. (4) (5)
3. Monitor radiation exposure
The best way to monitor staff doses is the comprehensive utilisation of personal dosimetry as available in your country. This is a legal requirement in most countries. Personal dosimeters, also called radiation badges, can be positioned outside the lead apron at neck level. The dosimeter estimates the dose to the eyes. More advanced eye dosimeters (that are attached to the frame of the lead glasses) have recently become available. Where personal dosimetry is not available, a dosimeter attached to the C-arm may provide an estimate of the dose received by medical personnel.
Address concerns and questions to appropriate radiation protection specialists
Every hospital or medical institution follow different policies or guidelines which can be very confusing. Concerns about radiation protection and personal protection equipment, however, should be addressed to the medical physicist or radiation safety officer of the hospital who are experts in radiation protection aspects. Where there are no such radiation protection specialists, concerns could be addressed to practitioners involved regularly in radiation related procedures such as radiologists. However, caution should be used since radiologists and radiographers are not necessarily experts in radiation protection.
Summary: Key points to remember for managing staff doses during interventional procedures.
The Radiation Dose Limit to the Lens of the Eye has been reduced due to new epidemiological evidence relating to the tissue reaction effects of doses to the lens of the human eye. Workplaces and medical staff are encouraged to adopt changes in advance of regulatory change to avoid or minimise health risks of radiation induced eye lens injury to medical workers.
If medical workers and workplaces are advised, taught of and execute the radiation protection principles and tools, it is still possible for medical staff (regularly exposed to radiation) to keep the annual radiation dose in the range of 0 to 5 mSv (against 20 mSv that is the dose limit) in a busy medical facility.
Some Recommendations are:
- Use lead glasses wherever lead aprons are required.
- Use protective shields (mounted shields/ flaps, ceiling suspended screens as applicable);
- Keep hands out of the primary beam (unless unavoidable for clinical reasons)
- Stand in the correct place: whenever possible on the side of the detector and opposite the X-ray tube rather than near the X-ray tube;
- Keep your knowledge of radiation protection issues up-to-date;
- Address your questions to appropriate radiation protection specialists;
- Always wear your personal radiation monitoring badge(s) and use them in the right manner;
- Know your equipment: make sure that fluoroscopy equipment is properly functioning and periodically tested and maintained;
- All actions to reduce patient dose will also reduce staff dose. And the potential liability for negligences cases in the future.
Gy: The gray (symbol: Gy) is a derived unit of ionizing radiation dose in the International System of Units (SI). It is defined as the absorption of one joule of radiation energy per kilogram of matter.
mSv: The millisievert (mSv) is a measure of the absorption of radiation by the human body.
(1) ICRP (2011), Statement on Tissue Reactions, Available online: http://www.icrp.org/docs/2011%20Seoul.pdf (07/09/2019)
(2) Linet MS, Kim KP, Miller DL, et al. (2010), Historical review of occupational exposures and cancer risks in medical radiation workers, Available online https://www.ncbi.nlm.nih.gov/pubmed/21128805?dopt=Abstract (01/09/2019)
(3) RCH (2011), Statement on Changes to Occupational Dose Limit for Lens of the Eye, Available online https://www.arpansa.gov.au/sites/default/files/rhc-statement-occupational-dose-limit-for-eye.pdf (01/09/2019)
(4) Ho, P., Cheng. S.W., Wu, P.M., et al., Ionizing radiation absorption of vascular surgeons during endovascular procedures, J. Vasc. Surg. 46 (2007) 455-459.
(5) Singer, G., Occupational radiation exposure to the surgeon. J. Am. Acad. Orthop. Surg. 13 (2005) 69-76.