|IAEA TECDOC REVIEW
|Year : 2015 | Volume
| Issue : 4 | Page : 168-171
Implication of new International Commission on Radiological Protection dose limit for eye lens: A brief review of TECDOC-1731
Ex-Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Web Publication||11-Feb-2016|
D-801, Synchronicity, Nahar Amrut Shakti Road, Chandivali Powai, Mumbai - 400 072, Maharashtra
Source of Support: None, Conflict of Interest: None
ICRP 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. In December 2013, IAEA brought out a TECDOC-1731, entitled “Implications for occupational radiation protection of the new dose limit for the lens of the eye,” providing interim guidance for application of the limit in operational settings of planned exposure situations. This brief review article is an attempt to bring out salient features of document for the benefit of the readers and operational radiation protection personnel.
Keywords: Dose limit, eye lens, implications, ICRP limits, occupational workers
|How to cite this article:|
Pushparaja. Implication of new International Commission on Radiological Protection dose limit for eye lens: A brief review of TECDOC-1731. Radiat Prot Environ 2015;38:168-71
|How to cite this URL:|
Pushparaja. Implication of new International Commission on Radiological Protection dose limit for eye lens: A brief review of TECDOC-1731. Radiat Prot Environ [serial online] 2015 [cited 2019 Sep 15];38:168-71. Available from: http://www.rpe.org.in/text.asp?2015/38/4/168/176153
| Introduction|| |
After reviewing recent epidemiological evidence suggesting lower dose threshold for some tissue reaction effects, particularly with very late manifestation such as eye lens, the International Commission on Radiological Protection (ICRP) issued, “Statement on Tissue Reactions” reducing the threshold on absorbed dose to 0.5 Gy, which was approved by the commission on April 21, 2011: “For occupational workers in planned exposure situations,” 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.
The previous limit recommended by ICRP (ICRP-60, 1991) on an equivalent dose to the lens of the eye of 150 mSv in a year was based on the dose threshold of 0.5–2 Gy for single acute exposure and 5 Gy for protracted exposure for detectable opacities of the eye lens. For inducing cataract (visual impairment), the assumed equivalent dose basis for the limit was 5 Gy for single acute exposure and 8 Gy following fractionated or prolonged exposure. Routine monitoring of the dose to the lens of the eye was not very common in view of the higher level of the dose limit.
The commission further emphasized the necessity of optimizing the protection of specific tissues such as lens of the eye and to the heart and the cerebrovascular system. Concern was expressed that in some complex interventional procedures in medical applications, it is likely that the absorbed doses may exceed the absorbed dose limit.
International Atomic Energy Agency (IAEA) held a technical meeting on implication and implementation of the limit in 2012 and consultants meetings in early 2013, and subsequently in 2013, the IAEA brought out a TECDOC-1731, “Implications for occupational radiation protection of the new dose limit for the lens of the eye,” providing interim guidance for use and comment.
This TECDOC-1731 (2013) provides interim guidance on the implications of 20 mSv/y for the lens of the eye for occupational radiation protection applicable to planned exposure situations. Guidance is also provided on the protection of the lens of the eye of emergency workers. This guidance does not apply to cosmic ray exposure of aircrew.
The interim guidance is intended for use by “regulatory bodies, licensees, and employers in hospitals, general industry, and nuclear installations; and management and personnel in such facilities, including radiation protection officers, industrial radiographers, medical physicists, cardiologists, interventional radiologists, and other medical specialists and health professionals involved in image-guided interventional procedures.”
| Structure|| |
Section 2 of this TECDOC provides a summary of the relevant biological information relating to the new dose limit for the lens of the eye. Section 3 provides guidance on the workers who might be affected by the change in this dose limit and the actions that should be taken to implement the change. It covers the optimization of protection (including training), monitoring, and health surveillance of these workers. There are three annexes in the document being reviewed. Annex I provides a summary of the occupational dose limits for exposure of the lens of the eye. Annex II provides typical values for equivalent dose to the lens of the eye per procedure in interventional radiology. Annex III provides guidance for medical practices where staff might receive significant doses to the lens of the eye.
The document also provides guidance on the medical surveillance requirements, dissemination of the information to all the stakeholders including the workers regarding the changes in the standards, local rules, and the controls being applied for compliance.
The document provides exhaustive references on various related aspects, applicable standards, references to the published eye lens dosimetry data on guided interventional radiology and cardiology procedures, on operational quantity Hp(3) for eye lens dosimetry, provides guidance for medical practices where staff work in close proximity to patients in image-guided interventional procedures, and the radiation-induced cataract risk, etc.
| Safety Assessment|| |
Safety assessment of a facility, at all stages is the major step to be taken to identify the ways in which exposures could be incurred, the magnitude and the overall provisions made in the facility to meet radiological protection and safety. Based on the assessment, radiation protection program is designed and optimized.
Situations in a new facility or an existing facility, where the eye lens of any worker is likely to be exposed are identified at each stage of the facility, particularly operational stage, and an assessment of the equivalent dose in mSv/year to the lens of the eye lens is made. Often, localized exposures, particularly to weakly penetrating such as beta particles or photons of low energies may be more restrictive than the limit on effective dose.
IAEA provides some guidelines to ensure that the revised equivalent dose limit for the lens of the eye is not exceeded, and exposures are adequately optimized by the licensee or the registrant of the facility.
- Ensure that equipment and installations are designed such that protection is optimized with due account being taken of the exposure of the lens of the eye
- Establish operational procedures, as necessary, to ensure that protection is optimized with due account being taken of the exposure of the lens of the eye
- Use of personal protective equipment by workers when the design of equipment and installations and the operational procedures are not sufficient to ensure that protection is optimized with due account being taken of the exposure of the lens of the eye
- Review of the safety assessment, taking into account of any generic safety assessments that may be available in the literature – to identify the groups of workers at risk and the doses that they might receive.
Category of workers for whom exposure of lens of eyes might be important and to be considered are:
- Those exposed to a relatively uniform whole-body (penetrating) radiation field
- Those exposed to highly nonuniform radiation fields in which the lens of the eye may be unintentionally exposed
- Those exposed to weakly penetrating radiation, such as beta particles or photons of low energies (below about 15 keV), significantly contributing to the dose to the lens of the eye, but not to the effective dose.
Exposures of the workers only to alpha particles or other high LET radiation need not be considered in view of their short range in the tissue. Assessment of the dose to the eye lens from exposure to neutrons is very complex to assess, and may not be significant.
In operational settings, shielding is generally erected between the source and the trunk. Often, face is not covered by the shielding (typically shielded fume hoods) or face is closer to the source than the trunk to facilitate clear visibility. The radiation field becomes nonuniform. An assessment of the dose received by the lens of the eyes may be made by suitable eye lens dosimetry technique.
| Some Specific Groups of Occupational Workers|| |
In ICRP publications 113 and 120, it was noted that cardiologists and the supporting staff working in catheterization laboratories in Latin America and Asia had more number of eye opacities due to improper procedures or not using proper protection tools. It was also noted that over the years, some of the exposures of the eye lens were in the range of 150 mSv/y.
- Staff working in the fluoroscopy-guided interventional procedures
- Staff working in radiation medicine procedures such as preparation/dispensing of radiopharmaceuticals, positron emission tomography, and computed tomography-guided procedures
- Staff working on manual brachytherapy and interventional cardiology/radiology
- Workers in medical cyclotron facilities.
| Occupational Workers in Nuclear Fuel Cycle Facilities|| |
In nuclear fuel cycle facilities, workers in nuclear fuel fabrication plants have higher potential for exposure of the eye lens from beta particles and low energy photons. Appropriately designed local shielding may be necessary while handling natural/depleted uranium or mixed fuel assembly lines in fume hoods/gloves boxes.
The target groups of workers for eye lens exposure are workers connected with decontamination and decommissioning activities in facilities in back-end of the fuel cycle.
| Workers Involved in Industrial Radiography|| |
Generally, unlike nuclear fuel cycle facilities, industrial radiography work, which is a part of NDT, the occupational exposures are whole body exposures and are generally higher. However, it is necessary to carryout eye lens dosimetry in typical exposure situations to ensure the dose to the lens is not significant from scattered radiations.
| Exposure of the Eye Lens in Accidental Situations|| |
It is likely that the lens of eyes of the workers get exposed during incidents/accidents involving radioactive materials. Typically, spillage of radiopharmaceuticals during their preparation can result in facial contamination of the staff and eye lens may get significant dose. Assessment of the dose to the eye lens from the whole body individual dosimeter may not be adequate from radiological safety considerations from mixed radiation fields.
| Comments|| |
The purpose of the TECDOC publication is to provide advice on the implications for occupational radiation protection of the new dose limit for the lens of the eye before detailed recommendations that may be incorporated into the upcoming IAEA safety guides. The document is very exhaustive and covers almost all the aspects necessary for effective implementation of the reduced equivalent dose limit for the lens of the eye.
Dosimetry and shielding are important considerations necessary in reducing the dose to the eye lens. The complexity of eye lens dosimetry continues to be an issue with respect to its reliability in view of the numerous variables which will affect the measured/estimated values. Varieties of eye lens dosimetry systems and eye lens shielding designs are being reported recently in the literature.
Until the development of reliable dosimetry system for eye lens dosimetry for regular use, personal protective equipment such as protective glasses should be used. Protective glasses made up of Perspex may be sufficient when the potential for exposure is only from beta particles, keeping in mind that bremsstrahlung radiation may likely to be generated by high energy beta radiation. The protective glasses containing lead may be required when the exposure is due to penetrating radiation such as low energy X-rays. It is important that the protective glasses need to be evaluated before use for its efficacy in shielding the eyes for the exposure situation.
Indian scientists have also undertaken studies for developing eye lens dosimeters, measurement/assessment of eye lens exposures in different operational settings such as medical applications of radiation and in nuclear fuel cycle facilities; and on the practical aspects of radiological protection of the personnel with potential for eye lens exposures.
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Conflicts of interest
There are no conflicts of interest.