Working group recommendation to the Agency.doc

596 views
576 views

Published on

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
596
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
6
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Working group recommendation to the Agency.doc

  1. 1. REVIEW OF STANDARDS OF PROTECTION FOR PREGNANT WORKERS AND THEIR OFFSPRING OUTLINE OF THE REPORT Page Executive Summary 2 A. Background 1. Statement of the problem 4 2. Action 13 from the International Action Plan 5 B. Summary of current national/international recommendations 1. ICRP Publications 6 2. IAEA Basic Safety Standards (BSS) 7 3. EU directive (96-29) 8 a. German Commission on Radiological Protection (SSK) 9 b. UK Ionising Radiations Regulations 1999 9 4. HPS/ANSI standard ..10 5. ILO Conventions and other documents 10 6. Evaluation of current standards 11 C. Summary of current knowledge and practice 1. Current practice in developed countries 12 2. UNSCEAR data – occupational exposures 12 3. External dose monitoring of the pregnant worker 15 4. Radionuclide intakes: doses to the embryo, fetus and child following exposures during pregnancy 15 5. Radionuclide intakes: doses to the infant from radionuclides in breast-milk 17 6. Radiation dose/effects 18 D. Working group recommendation to the Agency 1. Identification of exposure routes that contributing to exposures to embry/fetus and newborns – individual practices, sources of exposure and their significance 19 2. Summary and conclusions 25 3. Actions required at the international level 27 E. References 27 F Contributors to drafting and review 34 1
  2. 2. Executive Summary The recommendations of the International Commission on Radiological Protection (ICRP) and the IAEA Basic Safety Standards (BSS) make clear that the embryo and fetus should in be regarded as a member of the public when considering the protection of female workers who are or may be pregnant. The BSS note that the embryo and fetus should be “afforded the same broad level of protection as required for members of the public”. There is a requirement that women who may enter controlled or supervised areas are provided with information on the risks of radiation exposure of the embryo and fetus and that they should be informed of the importance of early notification of pregnancy. Similar guidance is included in national legislation, recommendations and guidance in a number of countries. However, there are a number of issues that require clarification, particularly:  the extent to which radiation exposure of the embryo and fetus may occur before pregnancy is declared;  the potential for doses to the embryo and fetus to exceed doses to the mother for intakes of particular radionuclides; and  the extent of additional dose to the newborn child from radionuclides transferred in breast milk and other maternal contact after birth.  the exact period over which restrictions/recommendations should apply, i.e.: o limit to apply to dose received in one year, o limit to apply during the remaining of the pregnancy, o limit to apply during all of pregnancy, or o limit to apply during all of pregnancy and the first 6 moths after birth. It can be concluded that, while the recommendations provided in the BSS are in general agreement with the international consensus on approaches to the protection of the pregnant or potentially pregnant worker, and are adequate for the purpose that they were intended to serve, more specific guidance is needed on this subject. It is recommended that a document be prepared that extends and clarifies previous advice in the context of the issues outlined above and considers the practical application of the advice for workers in different types of workplace (possibly a Radiation Safety Guide). In order to identify the important potential routes of exposure for the pregnant worker, four broad categories of radiation workplace have been classified. In the nuclear fuel cycle, in general, workers receive external and internal exposures, and the workforce involved in these practices is mostly male. Workers involved in the application of medical techniques, diagnostic and therapeutic, receive external and internal exposures to radiopharmaceuticals; in the medical field the number of female workers may be greater than males. In industrial uses, most of the doses come from external exposure, except for production of radioisotopes, where doses from internal exposure can be significant and also the proportion of female workers can be higher than in other industial practices. For exposure to natural sources of radiation other than the mining and processing of uranium ore, workers are exposed to external and internal sources of radiation, mainly from radon and its progeny. Significant numbers of female workers are involved in all activities except for uranium extraction and processing.. 2
  3. 3. The Consultant Group recommends: 1. that a technical document (working material) be drafted that clarifies how to implement the recommendations of the BSS (which needs no immediate changes) and to gives guidance on how to protect female workers and their offspring, 2. that a questionnaire be developed that queries member states regarding their practices with radioactive sources, external and internal exposures and the involvement of male / female workers, 3. that a Technical Meeting be held with representatives of various member states to discuss the technical document, and 4. that a Safety Guide be written based on the working material, the results of the member state questionnaire responses and the outcome of the Technical Meeting. 3
  4. 4. REVIEW OF STANDARDS OF PROTECTION FOR PREGNANT WORKERS AND THEIR OFFSPRING A. Background 1. Statement of the problem In facilities where workers are exposed to ionizing radiation, a system of radiation protection is implemented which is ultimately based on a balancing of the risks and benefits of the uses of radiation involved. More restrictive dose limits are set for members of the public than for workers and these have been applied also to the embryo and fetus (ICRP, 1991). It is well known that different individuals may have different levels of sensitivity to ionizing radiation; younger individuals and in particular the developing embryo/fetus are known to be generally more sensitive than adults. At low radiation doses, the main concern is radiation-induced cancer, whereas with higher doses, demonstrable physical effects may occur if certain thresholds of dose are passed. These thresholds will not be exceeded when applicable worker dose limits are properly enforced, and such effects will thus not be expected to be encountered under normal circumstances. Also, as will be discussed shortly, most countries recognize the developing infant as a member of the public and enforce an appropriately low dose limit for the embryo/fetus once pregnancy has been discovered and declared to the employer. In member states of the International Atomic Energy Agency (IAEA), there are many different industries and practices that involve the use of ionizing radiation and the potential exposure of female workers of childbearing age. The radiation sources and levels of exposure may vary significantly in different industries, such as those associated with the nuclear fuel cycle, industrial radiography, diagnostic and therapeutic medical applications, and others. Many member states have well developed regulations, recommendations, and practices for the recognition of this potential problem and protection of the mother and developing infant, but others may not have dealt extensively with this issue. In facilities where radiation exposure may occur, employers must always implement a formal program of radiation protection which includes monitoring, enforcement of limits on dose, formal training and periodic retraining of workers, and other activities. Employers have an ethical, and usually also a legal, responsibility to provide higher levels of protection to the pregnant worker and her developing infant. This protection practice may involve both internal and external sources of radiation, which may give a dose to the developing infant during pregnancy and for variable times after birth, including possible contributions resulting from breast-feeding and other maternal contact1 . All radiation workers have a responsibility to cooperate with their employers in the effective implementation of the radiation safety program at their workplace. Women of childbearing age have the additional responsibility of maintaining an awareness of how a pregnancy might lead to a requirement for increased 1 Note that for radionuclide intake during pregnancy, dose may be delivered in-utero to the embryo and fetus and for variable periods after birth to the child, depending on the half-life of the radionuclide and the duration of its retention in body tissues; hence we make reference in this report to ‘offspring’ doses. 4
  5. 5. protection during their work activities. In general, the woman should be encouraged to notify her employer as early as possible when a pregnancy is discovered. It should be emphasized, however, that such extra protection afforded to women during pregnancy should not lead to any discrimination that affects their rights as employees. It is an important human rights issue that men and women always have equal access to employment. Fair treatment of pregnant and potentially pregnant employees must always be balanced against the need of the employer to provide extra protection to this more sensitive population. In general, the application of the principle that doses should be as low as reasonably achievable (ALARA), as with cost/benefit analyses of working practices, will result in levels of protection for female workers that will ensure that doses to offspring will be well below dose limits. However, it is important to identify those situations of exposure in which doses to offspring may be significant. In this context, one factor that needs to be taken into account is that for some radionuclide intakes, doses to the offspring following exposures of the mother during pregnancy may exceed the corresponding doses to the mother. In accident situations, in which doses to the child may exceed dose limits, communication of dose and risk information to the employee and advice on possible action will depend on the availability of readily understandable information on biological effects and on uncertainties in dose assessments. The chemical toxicity of some radionuclides or compounds used in specific industrial procedures is not taken into account in radiation dose coefficients (e.g. those in ICRP Publications 88 and 95, to be discussed) and is not considered in this report. However, it should be recognized as important that the protection of the female worker and her offspring should include all forms of toxic effects; some elements such as uranium, fluorine, metallic elements, etc. may pose chemical as well as radiological hazards. For example, depending on the chemical solubility of certain compounds of uranium, radiation dose limitations alone may not provide sufficient protection to the pregnant worker and her developing infant. 2. Action 13 from the International Action Plan The first International Conference on Occupational Radiation Protection was held in Geneva, Switzerland from August 26-30, 2002. The meeting was organized by the IAEA and convened jointly with the International Labour Office (ILO). Subsequently, at the “First Meeting of the Steering Committee for the Action Plan for Occupational Radiation Protection” in Vienna, 4-6 February, 2004, a series of 14 Action Items were identified for follow-up action. Action 13 noted that “Presentations were made at the Geneva Conference which indicated that, in the case of certain radionuclides, some possible exposure routes for pregnant workers and their embryos and fetuses might not have been properly identified and that there might be a need for further international guidance on the formulation and application of standards for their protection.” The current IAEA Basic Safety Standards (BSS) and Radiation Safety Guide (RSG) documents contain numerous references to the pregnant and potentially pregnant worker and provide general guidance for radiation protection practice in member states on this issue. As seen in section B.2, below, the guidance is often not clear, however, in regards to specific practices, numerical dose limits, declaration of 5
  6. 6. pregnancy, and other central issues. It was thus thought prudent to “…review current information on this issue in order to determine whether the issue warrants action at the international level”, and to identify important routes of exposure to ionizing radiation for the pregnant woman, embryo/fetus, and newborn infant. The IAEA thus formed a working group to review the current state of the art of the assessment of radiation doses to the developing infant (including the embryo/fetus during gestation as well as the newborn infant) and also to review current regional and international recommendations and practice in the area of the protection of the pregnant and potentially pregnant worker. This report is the result of the work of this working group in November and December of 2005. B. Summary of current national/international recommendations and guidance 1. ICRP Publications The ICRP publishes a variety of documents with important data and recommendations regarding radiation protection practice for the international community. ICRP recommendations form the basis for the regulatory structure of most countries in the protection of radiation workers and the public from sources of ionizing radiation. Some supporting ICRP documents contain models and data that assist in various aspects of radiation protection practice. Several recent documents of the ICRP address the issue of the protection of the pregnant and potentially pregnant worker and also protection during breast- feeding. ICRP Publication 84, “Pregnancy and Medical Radiation” – This document gave some philosophical basis and recommendations for the protection of pregnant or potentially pregnant patients who might be exposed to internal or external radiation in the practice of medicine. The document presents some material regarding the biological effects of in-utero irradiation and recommendations for the management of patients who may receive a radiation dose to their embryo/fetus in the course of their medical treatment. ICRP Publication 88, “Doses to the Embryo and Fetus from Intakes of Radionuclides by the Mother” – This document provided modelling results for the placental transfer of radionuclides from the mother to the fetus and comprehensive treatment of dose models for the fetus, including dose from maternal organs to the fetus and dose to the fetus from incorporated radionuclides, including dose from incorporated radionuclides that may be delivered to the offspring after birth. Many of the tabulated dose coefficients (Sv per Bq intake by the mother) presented in this report, relating to ingestion or inhalation of radionuclides in the workplace, were used in forming the conclusions in this report. (See Section 4.) ICRP Publication 90, “Biological Effects after Prenatal Irradiation (Embryo and Fetus) – This publication provides an overview of the knowledge regarding possible short and long term effects of the irradiation of the embryo and fetus. ICRP Publication 95, “Doses to Infants from Ingestion of Radionuclides in Mothers’ Milk” – This document is similar to ICRP 88, in that it provides tables of dose coefficients (Sv to the 6
  7. 7. child per Bq intake by the mother) for a range of radionuclides, considering acute or chronic intake by ingestion or inhalation during or before pregnancy as well as during breast-feeding. (See Section 5.) 2005 Draft Recommendations: In the 1990 recommendations of the ICRP (ICRP, 1991), it was concluded that there is no reason to distinguish between the two sexes in the control of occupational exposure. However, if a woman has declared herself pregnant, additional controls should be considered to protect the unborn child. The ICRP policy is that the methods of protection at work for women who may be pregnant should provide a standard of protection for any conceptus broadly comparable with that provided for members of the public. The view is that this policy will be adequately applied if the mother is exposed, prior to the declaration of pregnancy, under the system of protection recommended by the Commission, including the recommended dose limits for occupational exposure. Once pregnancy has been declared, and the employer notified, additional protection of the fetus should be considered. This additional protection is outlined more simply in draft new recommendations (ICRP, 2005), curently available on the ICRP web-site (www.icrp.org), than in Publication 60 (ICRP, 1991). The new draft refers to the control of working conditions of a pregnant worker, after declaration of pregnancy, such that it is unlikely that the additional dose to the fetus will exceed about 1 mSv during the remainder of pregnancy. It is made clear that this does not mean that pregnant women should avoid work with radiation but that working conditions should be carefully reviewed and that, in particular, the probability of high accidental doses or radionuclide intakes should be insignficant. It should be noted that the new draft recommendations are under revision to take into account extensive international comment and new recommendations will not be avialable until 2007 or later. 2. IAEA Basic Safety Standards (BSS) – the IAEA has published these requirements regarding the safe uses of radiation, based on international consensus positions on the various topics of concern. A number of references are made to the protection of female workers and their offspring: a. SS-115, Sec I.16-I.17 “A female worker should, on becoming aware that she is pregnant, notify the employer in order that her working conditions may be modified if necessary. The notification of pregnancy shall not be considered a reason to exclude a female worker from work; however, the employer of a female worker who has notified pregnancy shall adapt the working conditions in respect of occupational exposure so as to ensure that the embryo or foetus is afforded the same broad level of protection as required for members of the public.” (The same information is also provided the IAEA Radiation Safety Guide 1.1, Section 2.39). b. SS-115, Sec I.27: “Employers, in co-operation with registrants and licensees, shall… provide to female workers who are liable to enter controlled areas or supervised areas appropriate information on: (i) the risk to the embryo or foetus due to exposure of a pregnant woman; (ii) the importance for a female worker of notifying her employer as soon as she suspects that she is pregnant; and (iii) the risk to an infant ingesting radioactive substances by breast feeding;” (The same information is also provided the IAEA Radiation Safety Guide 1.1, Section 5.33). 7
  8. 8. c. RS-G-1.1, Sec 3.8: “In general, the dose limits apply equally to male and female workers. However, because of the possibility of a greater sensitivity of the foetus to radiation, additional controls may have to be considered for pregnant workers.” d. RS-G-1.1, Sec 7.15: “The occupational physician should also be able to advise management on the need for any particular precautions or procedures regarding the working conditions of pregnant women, and to advise pregnant workers of any particular precautions that they themselves should take.” e. RS-G-1.1, section 2.28: “There may also be a need to consider the management of female air crew who have declared themselves to be pregnant” 3. EU directive (96-29) Article 10 of the 1996 Euratom Basic Safety Standards states that: “As soon as a pregnant woman informs the undertaking in accordance with national legislation and/or national practice, of her condition, the protection of the child to be born shall be comparable with that provided for members of the public. The conditions for the pregnant woman in the context of her employment shall therefore be such that the equivalent dose to the child to be born will be as low as reasonably achievable and that it will be unlikely that this dose will exceed 1 mSv during at least the remainder of the pregnancy. As soon as a nursing woman informs the undertaking of her condition she shall not be employed in work involving a significant risk of bodily radioactive contamination.” 8
  9. 9. Article 22 states that: “Member States shall require the undertaking to inform exposed workers, apprentices and students who, in the course of their studies, are obliged to use sources on:… in the case of women, the need for early declaration of pregnancy in view of the risks of exposure for the child to be born and the risk of contaminating the nursing infant in case of bodily radioactive contamination.” The EU directives have been reflected in specific recommendations by the German Commission on Radiological Protection (SSK) and the UK Health and Safety Executive: a. German Commission on Radiological Protection (SSK) In 2004 the German Commission on Radiological Protection (SSK) published the recommendation "Radiological Protection of the Unborn Child" including scientific grounds for this recommendation. This recommendation mainly examines the implications for incorporation monitoring to guarantee that the limit for the committed effective dose to the embryo / fetus of 1 mSv is met. For this two intake scenarios for the occupationally exposed mother are considered: 1) continuous intake by inhalation with a constant intake rate over 10 years before pregnancy and during the first 10 weeks of pregnancy; 2) acute intake by inhalation during the first 10 weeks after conception. It was assumed that after 10 weeks the pregnant worker has declared her pregnancy; the German Radiation Protection Ordinance demands that no occupational intake of radionuclides by the pregnant worker should occur after the declaration of pregnancy. For these two intake scenarios, maximum annual committed effective doses to the mother were calculated with the biokinetic and dosimetric models given in ICRP Publication 88, which guarantee that the committed effective dose to the embryo and fetus does not exceed 1 mSv. It was recommended that for each radionuclide and absorption type considered in ICRP Publication 88, the most restrictive value may not be exceeded. To ensure comliance, For this the incorporation monitoring should be organized such that this dose level can be detected. At the present time, however, the German ministry has not adopted the SSK recommendation in establishing a regulation for incorporation monitoring. b. UK Ionising Radiations Regulations 1999 and NRPB guidance on application of dose coefficients for the embryo and fetus In the UK, work with ionising radiations is subject to the Ionising Radiations Regulations 1999 (IRR99; GB Parliament, 1999). The Regulations set down requirements for the safety of people who work with ionising radiation, including work with radioactive substances. IRR99 require radiation employers to undertake a risk assessment prior to starting a new work activity involving work with ionising radiation and to take all reasonable steps to 9
  10. 10. restrict so far as is reasonably practicable the exposure to ionising radiation of employees and other workers arising out of their work activity. In addition, there is the requirement that once a female employee has declared herself pregnant, the radiation employer must control her working conditions so that the dose to the fetus is unlikely to exceed 1 mSv during the remainder of the pregnancy. Guidance is given on risk assessment for pregnant employees, together with appropriate control measures (Health and Safety Commission, 2000). The radiation employer should consult a suitable Radiation Protection Adviser for advice on the risk assessment and necessary control measures. All employers must inform female workers of the possible risk to the fetus of exposure during pregnancy and of the importance of informing their respective employer when they become aware that they are pregnant. This requirement to give specific information is in addition to the general requirement for information, instruction and training for all employees who work with ionising radiation. NRPB (2005) issued guidance on the application of the ICRP Publication 88 (2001) dose coefficients for the embryo and fetus following radionuclide intakes by the mother. The NRPB report drew attention to those radionuclides for which doses to the offspring could exceed doses to the mother so that protection based on estimated doses to the mother may not be sufficient. The advice given was that employers and their Radiation Protection Advisers should review working practices with these radionuclides. 4. HPS/ANSI standard – the U.S. Health Physics Society has developed a document which gives dose coefficients and guidance on the calculation of fetal doses in: a. Radiation Therapy b. Diagnostic Radiology c. Nuclear Medicine d. Occupational Radiation Exposure The document also summarizes current knowledge on fetal dose and possible biological effects. 5 ILO Conventions and other documents Several ILO Conventions and documents were revised for requirements and guidance related to the protection of the pregnant worker, embryo and foetus, namely:  Radiological Protection Convention 115 (1960)  Occupational Health Convention 161 (1985)  Working Environment Convention 148 (1977)  Employment Injury Benefit Convention 121(1964)  Occupational Cancer Convention 139 (1874)  Guidelines for the Radiation Protection of Workers in Industry(Ionising Radiation). OSHS n.62 (1989)  The provisions of the Basic Safety Standards for Radiation Protection relevant to the protection of workers against ionising radiation. OSHS n.55 (1985) 10
  11. 11. There is no provision for the protection of the pregnant worker, embryo and foetus in documents 1 to 6 above. There is a paragraph in document 7 stating that: "....the Basic Safety Standards do not make separate provision for women of reproductive capacity, except that they insist on the importance of the uniformity of the distribution of exposure for the protection of the embryo before a pregnancy is know. When the woman is pregnant she should only work in Working Condition B..." 6. Evaluation of current standards There is general agreement in the radiation protection community that the embryo/fetus should be afforded the same level of protection as members of the general public and protected at approximately a 1 mSv/year dose level. Women should be encouraged to declare their pregnancies as early as possible after discovery of pregnancy, to permit the employer to provide this level of protection to the embryo/fetus. The requirements provided in the BSS are in agreement with the general international consensus on the approaches to the protection of the pregnant or potentially pregnant worker, and are basically adequate for the purpose that they were intended to serve. However, much more specific guidance and clarity of methods for implementation of these practices is needed for the member states. A document is needed that contains major elements of the technical basis for the protection of workers and that spells out methods for implementation of these approaches to workers in different types of workplace (possibly a Radiation Safety Guide). Further clarity is needed as well on two technical issues which are involved in this protection practice, which have been raised by the different documents evaluated above. A potential problem exists in that in the ICRP literature and the EU directive as written, the 1 mSv dose limit is only applied to the period of gestation after pregnancy is declared (and other exposures that may have occurred in early pregnancy are not included in the total estimate of fetal dose). The German recommendations and current USA regulations, on the other hand, apply the dose limit for internal exposures (external exposures also, in the US) to the whole of pregnancy, i.e. including the period before pregnancy is declared. It is also possibly problematic to consider the use of this dose limit for long-lived radionuclides that may be incorporated into the embryo/fetus or newborn and deliver a dose over a long period of time (up to 70 years after birth). The definition of “offspring” includes the infant both during pregnancy and after birth. An important issue thus becomes how to apply the 1 mSv dose limit in a uniform manner over the year during which the mother is pregnant, when she may declare her pregnancy at various times during the gestation period, and considering also the fact that there may be radionuclides present in her body from previous exposures – even those before conception - that may contribute to the total dose that the offspring receives. 11
  12. 12. C. Summary of current knowledge and practice 1. Current practice in developed countries The working group included members representing the countries of Brasil, France, Germany, the UK, and the USA. In these countries, practice generally reflects the IAEA position that “the embryo or fetus [should be] afforded the same broad level of protection as required for members of the public.” Exact implementation varies, but in general, women are strongly encouraged or required to notify their employers as soon as possible when a pregnancy is declared. Thereafter, an enhanced level of protection is afforded the fetus of the declared pregnant worker, with the ICRP recommended dose limit of 1 mSv/year for the general public being generally applied to the protection of the fetus. The declared pregnant worker may be restricted from certain work activities, particularly those involving higher radiation exposures or exposures to open sources of radioactive material. Restriction of work activities are imposed to ensure that the 1 mSv level will not be exceeded. Awareness of the worker’s rights to fair employment is always considered even if work duties must be modified for some period of time. 2. UNSCEAR data – occupational exposures The UNSCEAR 2000 Report has classified the practices resulting in occupational exposures to radiation in four broad categories of source of exposure: nuclear fuel cycle, medical uses, industrial uses and natural sources of radiation. The doses estimates reported in the Report 2000 relate to the period from 1990 to1994. a. Nuclear Fuel Cycle (UNSCEAR 2000) - A significant source of occupational exposure is the operation of nuclear reactors to generate electrical energy. This involves a complex cycle of activities, including the mining and processing of uranium ore, uranium enrichment, fuel fabrication, reactor operation, fuel reprocessing, waste handling and disposal, and research and development activities. In general, the number of female workers involved in this practice is small compared to male workers. The estimated average annual effective dose for measurably monitored workers involved in mining and processing of uranium ore is about 5 mSv, in a range from 0.3 mSv to 15 mSv), the exposures result from external radiation, inhalation of radioactive dust particles, mainly insoluble uranium compounds (Type S), and inhalation of radon and its progeny. The annual effective dose for measurably monitored workers involved in uranium conversion and enrichment is in a range from 0.4 to 1 mSv. In this practice the UO2 is converted to UF6, for which internal exposure is limited based on chemical toxicity instead of radiological toxicity. Occupational exposures occur during both the conversion and enrichment stages, with, in general, external radiation exposure being more important than internal radiation exposure. Workers may, however, be exposed to internal irradiation, particularly during maintenance work or in the event of leaks. The fuel used in light water reactors (LWRs) and in fast breeder reactors (FBRs) may be a mixture of uranium and plutonium fuels. The principal source of exposure during fuel fabrication is uranium (after milling, enrichment, and conversion, most decay products have been removed), which may involve external 12
  13. 13. exposure from gamma rays and intakes of airborne activity. The average annual effective dose to measurably monitored workers involved in fuel fabrication is estimated to be about 2 mSv, in a range from 0.42 mSv to 5 mSv). In reactor operation, the main source of occupational exposure is, in general, external irradiation, mainly from activation products in the coolant and coolant circuits, most of the exposures arise during maintenance activities. The annual effective dose to measurably monitored workers averaged over all reactors is 2.7mSv. There are some differences between reactor types in the magnitudes of the doses. For heavy water reactors (HWRs), internal exposure can be a significant component of exposure, principally from intakes of tritium produced by activation of the heavy-water moderator. The average annual effective dose to monitored workers can exceed 10 mSv. The reprocessing of irradiated spent fuel from nuclear power facilities to recover uranium and plutonium can result in doses due to internal and external exposure. The average annual effective dose to measurably monitored workers is 2.8 mSv. b. Medical Uses of Radiation (UNSCEAR 2000) – Occupational exposures may occur in diagnostic radiology, dental radiology, nuclear medicine (diagnostic and therapeutic), radiotherapy and biomedical research laboratories. In such practices the number of female workers is significantly higher than in some other practices. For diagnostic radiology there are three general procedures that constitute sources of exposure: radiography, fluoroscopy, and special examinations. In radiography, including computed tomography and mammography, the exposure of staff is usually low, because the primary x-ray beam is highly collimated, and scattered radiation levels are low. In all such examinations, leakage of radiation has been reduced to near zero and staff in the control room of a properly designed facility should receive annual doses below 1 mSv. Special examinations are taken to include cardiac catheterization, angiography, and interventional procedures. For these procedures fluoroscopic times may be long and the radiographic exposures can be numerous. Staff are nearly always present in the room close to the patient, and it is difficult to shield against scattered radiation. Staff exposure rates associated with the examinations in such rooms can be 2 mGy h-1 or more, depending on location and fluoroscopic technique. Cardiac catheterization, in particular, can result in relatively high exposures. Procedures involve not only radiography and fluoroscopy, some also require cineradiography. During cineradiography, the table-top air kerma rate may vary from 0.2 to 1 Gy min-1 . Although an examination may require only 30-40 seconds of cinegraphic time, total exposures to staff can be high. The occupational doses are strongly influenced by the equipment design and technical settings, clinical protocol, to some degree by clinical experience and also the extent of use of protective measures. Some physicians have been resistant to the use of protective measures that they consider would interfere in their ability to obtain the best possible information. If protective measures are not undertaken, annual doses can rise to values above 20 mSv. 13
  14. 14. Occupational exposure in dentistry is from scattered radiation from the patient and leakage from the tube head, although the latter should be insignificant with modern equipment. A majority of dental practitioners do not receive measurable doses. Occupational exposure in nuclear medicine is mainly due to external radiation, although internal exposure can occur, more specifically for the staff involved in the preparation and assay of radiopharmaceuticals or working in departments where radioiodine treatments are performed.. The highest occupational exposures are to radiopharmacy staff and individuals involved in administering radio-pharmaceuticals to patients. The annual dose for these occupational groups can reach values up to 5 mSv. In general, 85% of the dose is from exposure to 99m Tc, 10% from 18 F, and 5% from other radioisotopes, such as 123 I, 201 Tl, 51 Cr, 67 Ga, 131 I. In radiotherapy personnel should not normally be present in the treatment room when external beam therapy is being used, with the possible exception of low-energy (50 kVp and less) x-ray contact therapy units, which are sometimes used for intracavitary treatments. Some exposures can, however, occur from 60 Co teletherapy units as a result of leakage while the source is in the off position and from radiation that penetrates the barrier during use. The types of exposure from linear accelerators, betatrons, and microtrons depend on the type of beam (photon or electron) and the beam energy. Below 10 MeV, exposure will result only from radiation that penetrates the protective barrier. Above 10 MeV, photonuclear reactions can produce neutrons and activation products. The neutrons can penetrate the protective barrier while the unit is operating. The exposures, however, are normally low. The data on occupational doses in radiotherapy show that the typical dose below or up to 1 mSv. Few beam radiographers, radiotherapists, technicians, or other support staff receive annual doses exceeding 1 mSv. With brachytherapy procedures, some theatre and ward nurses receive over 5 mSv in a year. In biomedical research laboratories the doses result mainly from exposures to 3 H, 14 C, 32 P, 35 S, 45 Ca and 123 I. The average annual effective dose to measurably exposed workers is relatively small, around 1 mSv. c. Industrial Uses of Radiation (UNSCEAR 2000) - Occupational exposures in industrial uses of radiation are due to external exposure, except for radioisotope production where internal exposures can occur. The average annual effective dose to measurably exposed workers is about 2 mSv in industrial irradiation (0.02 mSv-3 mSv), the average value in industrial radiography is 3 mSv (0.5 mSv-20 mSv), in luminizing the annual doses are in a range from 0.3 mSv to 1 mSv. The average annual effective dose to measurably exposed workers in well logging is 0.8 mSv (0.1 mSv-9 mSv) and 2 mSv in accelerator operation (0.1 mSv-2.7 mSv). The average annual effective dose to measurably exposed workers involved in radioisotopes production is 3 mSv (1 mSv-7 mSv). Considerable attention has been given by some investigators to 131 I external exposures and intakes, since the volatility of iodine makes its compounds readily available for intake by inhalation . Significant intakes of 131 I have been recorded during in-vivo counting and in-vitro bioassay, with dose reconstructions performed. In general, the internal doses are not evaluated in routine basis. Some authors have reported 14
  15. 15. significant values of internal dose due to intakes of 131 I, such as 4 mSv or even higher (Gaburo et al., 2003 and Alirezazadeh et al., 2003). d. Natural Sources of Radiation – a large number of workers are exposed to enhanced natural sources of radiation; most of them are involved in uranium mining and processing operations. In many cases, doses are mainly due to exposure to 222 Rn and its short-lived decay products. Annual effective doses can reach values above 20 mSv (Colgan et al, 2004; Khater et al., 2004). The reported values of annual effective doses due to radon exposure in workplaces other than mines are above to 20 mSv (Soto et al., 1995; Lettner et al, 1996; Stueber et al., 2000; Trautmannsheimer et al., 2002; Kávási et al., 2003). For cosmic ray exposure to aircrew, the average annual effective dose is typically 1-2 mSv for those on short-haul flights and 3-5 mSv for those on long-haul flights (UNSCEAR 2000). 3. External dose monitoring of the pregnant worker Employers, as well as self-employed individuals, are responsible for arranging for the assessment of external doses that may be received, on the basis of individual monitoring when appropriate. This responsibility includes ensuring that adequate arrangements are made with appropriate dosimetry services under an adequate quality assurance program. When the pregnancy is declared and notified, two components of external dose must be taken into account; 1) external irradiation of the mother resulting from the continuation of her previous work, and 2) external irradiation of the embryo/fetus from radionuclides in maternal tissues which may contribute to total effective dose. For the first component, it is the responsibility of the employer to adapt the working conditions in respect of occupational exposure so as to ensure that the embryo or fetus are afforded the same broad level of protection as required for members of the public. Appropriate dosimeters used to record fetal dose may be positioned for:  an external exposure to the whole body, if the source of the radiation is isotropic,  an external exposure to the abdomen, if not. The second component of external dose to the fetus, from radionuclides in maternal tissues, is included in the dose coefficients which are used to determine the dose to the embryo/fetus and newborn from radionuclides ingested or inhaled by the mother, as will be described in the next section. 4. Radionuclide intakes: doses to the embryo, fetus and child following exposures during pregnancy In 2001 ICRP in its Publication 88 published biokinetic and dosimetric models for the calculation of doses to the embryo and fetus from intakes by the mother as well as dose coefficients for various intake scenarios by the mother. 15
  16. 16. Doses to the embryo, taken to be up to the end of the 8th week of pregnancy, were assumed to be the same as the dose to the uterus wall. The developing conceptus becomes embedded in the uterus wall and by the end of the 8th week has a mass of less than 10 g. For the fetal period, radionuclide transfer across the placenta and retention in developing fetal tissues were represented by element-specific models in cases where sufficient human data were available. This applies to tritiated water, and isotopes of cesium, iodine and the alkaline earth elements (calcium, strontium, barium, radium). For all other elements, a general approach was adopted based on the use of relative concentrations of radionuclides in the fetus and mother. These concentration ratios were based mainly on reviews of data from animal studies. Doses to fetal tissues from activity retained in the fetus were calculated using a series of computer phantoms of the fetus for various times of gestation. Irradiation of the fetus resulting from radionuclide retention in the placenta and maternal tissues was taken into account, using phantoms for three stages of pregnancy (end of the first, second and third trimesters). Committed effective doses to the newborn child, from radionuclides retained in the body at birth, were calculated using models developed previously for infants, children and adults. The fetal dose coefficients in ICRP 88 combine each of these contributions, giving the total committed effective dose received in utero and after birth for various acute and chronic intake scenarios of radionuclide inhalation or ingestion by the mother. Additionally, doses coefficients were given for the organ receiving the highest in utero dose and for the brain during the time period between week 8 and 15 after conception, the most sensitive period for effects on mental development (see below). Comparisons of fetal dose coefficients with corresponding adult dose coefficients show that doses received by a woman from intakes before or during pregnancy will in most cases be substantially greater than doses to her fetus. This comparison is made with the reference adult because ICRP at present does not calculate doses separately for males and females. Comparisons of infant doses with doses specific to female adults would result in different numerical values but the same general conclusions. As shown in Tables 1 and 2, doses to the offspring can exceed doses to the mother for a number of radionuclides. In particular, the requirements of skeletal development during fetal growth, particularly in late pregnancy, can lead to significant uptake of radioisotopes of phosphorus and of calcium and, to a lesser extent, other alkaline earth elements. Uptake of radioisotopes of iodine by the fetal thyroid can also lead to greater doses to the fetus than to the mother. The fetal thyroid begins to accumulate iodine at about 11 weeks post- conception. During embryonic and early fetal development, doses to the fetus from radioisotopes of iodine will be low and it is only later in pregnancy that uptake by the fetal thyroid gland can lead to doses exceeding corresponding doses to the mother. Other radionuclides for which doses to the fetus can exceed doses to the mother include tritium as tritiated water, carbon-14 and sulphur-35. In general, chronic exposures are likely to occur only before pregnancy or during early in utero development when the pregnancy has not yet been recognized. For chronic intakes before conception the committed effective dose to the fetus may be larger than the annual committed effective dose to the mother in the case of nickel isotopes which, due to their long effective half- lives, can accumulate within maternal tissues and are readily transferred to the fetus. 16
  17. 17. 5. Radionuclide intakes: doses to the infant from radionuclides in breast-milk ICRP Publication 95 (2004) considers transfer of radionuclides to the infant in breast-milk for intake times before or during pregnancy as well as during lactation. The dose coefficients (Sv Bq-1 ) given are doses to infants per unit intake by their mothers. The dose coefficients are thus the dose to the newborn infant from unit intake by the mother. The quality of the available data on the transfer of different elements and their radioisotopes to milk varies widely. However, there is sufficient quantitative information in most cases on which to base specific estimates of the rate of transfer from the mother’s blood to milk. In many cases, there are good human data on the transfer of stable elements to breast-milk. There are also good human data for the transfer of cesium-137 and iodine-131 to milk. In a number of cases, including the actinide elements, reliance must be placed on animal data. Exceptional cases for which data were judged to be insufficient to specify individual values for transfer to milk are zirconium, niobium, ruthenium, antimony, polonium, thorium and uranium. For each of these elements, total transfer to milk (i.e. without radioactive decay) was assumed to account for 5% of the amount absorbed to maternal blood. This default was based on limited element specific data or information on more frequently studied chemical or physiological analogues. The dose coefficients in ICRP Publication 95 (2004) were calculated assuming that consumption increases linearly over the first week of life to 800 ml d-1 and continues at this rate to 6 months (26 weeks) after birth. No account is taken of the subsequent reduced consumption during weaning. However, it is recognized that daily production of milk varies substantially among individuals and that there is an extremely wide variation throughout the world in the duration of breast-feeding and the time at which women choose to begin weaning their child. The time taken to introduce solid food and cease milk consumption is also very variable. In applying the ICRP dose coefficients the uncertainties associated with these differences should be borne in mind and continued feeding beyond 6 months may need to be taken into account in specific circumstances. Publication 95 (ICRP, 2004) gives some guidance on the assessment of doses in situations that differ from the default assumptions. The overall conclusion from the dose coefficients given in Publication 95 (ICRP, 2004) is that for most of the radionuclides considered, doses to the infant from radionuclides ingested in breast-milk are estimated to be small in comparison with doses to the reference adult. On the basis of the models developed in this report, it is only in the cases of tritiated water, 45 Ca, 75 Se and 131 I that infant doses may exceed adult doses, by ratios of between 1 and 3, applying to maximum transfer occurring after maternal intakes by ingestion shortly after birth (Table 3). Ratios of infant to reference adult doses are generally lower for intakes by inhalation than for ingestion. Comparisons with Publication 88 doses to the offspring due to in-utero exposures show that in most cases these are more important than doses that may result from breast feeding; exceptions include 60 Co, 131 I and 210 Po. Publication 95 (ICRP, 2004) also considers external doses to the infant from radionuclides in the mother’s body. These example calculations of external photon doses to the infant from radionuclides in maternal tissues, using a modified voxel phantom, show that in some cases it is possible for external dose to dominate the overall effective dose to the infant. This applies, for 17
  18. 18. example, to inhalation of insoluble cobalt-60 by the mother, while for other examples considered in the report, external dose is small compared with the dose resulting from radionuclides ingested in breast milk. 6. Radiation dose/effects Known and theoretical risks related to irradiation of the embryo and fetus include: a) Embryonic loss and stillbirths b) Induction of congenital malformations c) Neurobehavioral defects, including mental retardation associated with microcephaly d) Recoverable and nonrecoverable growth retardation e) Development of cancer post-partum The first four of these categories involve demonstrable physical effects, generally associated with a dose threshold; the fifth is a stochastic effect, which has been difficult to express quantitatively. Brent (2005) notes that epidemiological studies have indicated that exposures of ionizing radiation below the 0.05 Gy level probably will not cause demonstrable physical effects. Animal studies seem to indicate that the threshold might be even higher, perhaps around 0.1-0.2 Gy, and also indicate that fractionation and protraction of radiation exposure further diminish the probability of induction of these effects. The review by ICRP in Publication 90 (2003) of data from studies of the Japanese survivors of the atomic bombings at Hiroshima and Nagasaki now more clearly supports a dose-threshold of at least 300 mGy for the induction of severe mental retardation after irradiation in the most sensitive prenatal period (8 – 15 weeks post-conception) and therefore the absence of an effect at low doses. The associated data on IQ losses estimated at around 25 points per Gy are more difficult to interpret and a non-threshold dose-response cannot be included. However, even in the absence of a true dose threshold, any effects on IQ following in utero doses of a few tens of mGy would be undetectable and therefore of no practical significance. Information on cancer risks following in utero irradiation is available from studies of prenatal diagnostic x-ray exposures, as well as studies of the Japanese survivors. The largest study of the effects of prenatal diagnostic x-irradiation is the Oxford Survey of Childhood Cancers (OSCC), a national case-control study of childhood cancer mortality carried out in the United Kingdom. Reviewing the available data from the OSCC and other studies, Doll and Wakeford (1997) concluded that there is evidence that low dose irradiation of the fetus (doses of about 10 mGy), particularly during the last trimester of pregnancy, causes an increased risk of cancer in childhood (<15 years of age). However, the ICRP (2003) has drawn attention to differences between studies in the relative risks estimated for leukaemia and solid cancers and concluded that the data provide an insufficient basis for the specification of risks of in utero irradiation of individual organs and tissues. Data on the effect of postnatal age at irradiation from follow-up studies of the Japanese survivors show that relative cancer risks are greatest for younger ages, for a number of cancer types including carcinoma of the colon and stomach (UNSCEAR, 2000). The A-bomb data suggest that the lifetime risk of cancer form in utero exposure may be similar to that from exposure in early childhood. Emphasizing the limitations of the available data, the 18
  19. 19. ICRP concluded that it is reasonable to assume that the cancer risk associated with irradiation in utero or in early childhood is, at most, a few times that of the population as a whole. Use of these potential risk values in standard setting and communication of them to the potentially pregnant worker should consider their significant uncertainties, as noted by Brent (2005). A. Working group recommendation to the Agency 1. Identification of exposure routes that contributing to exposures to embryo/fetus and newborns – individual practices, sources of exposure and their significance In this section, significant sources of radiation dose to the embryo/fetus and the newborn will be identified for the most important practices involving the use of ionizing radiation. In each section, four categories of exposure will be identified and important pathways and radionuclides will be discussed in each category. The categories are: In-utero: external exposures: sources of radiation external to the body of the mother, irradiating both maternal tissues and the embryo/fetus. In-utero: radionuclide incorporation: incorporation of radionuclides by the mother, with transfer to the fetus through the placenta, and including irradiation of the fetus by penetrating radiation from radionuclides deposited in maternal tissues. Newborn: breast milk transfer: intake of radionuclides by the newborn via transfer from the mother’s system to the breast milk and ingestion during breast feeding. Newborn: external exposure from maternal tissues: irradiation of the newborn from penetrating radiations in maternal tissues. a. Nuclear Fuel Cycle i. Uranium Mining and Processing – The number of female workers involved in this area of the nuclear fuel cycle is in general small compared to the number of male workers. Some significant dose pathways may exist, however, for the pregnant or potentially pregnant worker in this situation. In-utero: external exposures: As noted above, the annual effective dose to workers involved in uranium mining and processing activities is about 5 mSv. Some data are available that indicate that internal exposures from radon account for about 60% of workers’ total annual effective dose (Health Canada, 2000). For underground mines, this contribution may be higher than for surface mines. Therefore, average fetal doses of less than 5 mSv/year may be received for pregnant workers in this occupation. In-utero: radionuclide incorporation: Exposures of the mother to radon and radon progeny result in a significant lung dose to the mother, but only very low internal incorporation of the radionuclides and thus uptake by the fetus. Accumulated radon progeny in maternal lung tissue, from current or previous exposures, could potentially result in some penetrating radiation dose to the fetus. Model results show, however, that, 19
  20. 20. for the mother’s tissues, this is a very small fraction of the lung dose, and thus can be assumed to make a negligible contribution to dose received by the fetus. For inhalation of insoluble forms of uranium, the dose to the fetus is smaller than that to the mother. The mine environment also contains significant quantities of 226 Ra, which is generally in more soluble forms. 226 Ra doses to the fetus, as noted above, may be similar to those of the mother for continuous ingestion intakes occurring over longer periods, significantly lower than maternal doses for long term continuous inhalation of insoluble forms of 226 Ra, or as much as about twice that for the mother for acute ingestion intakes occurring in the later stages of gestation. Other uranium and radium progeny, such as 210 Po and 210 Pb, may be present in mine environments at significant levels; the NRPB guidance document from which Tables 1 and 2 were taken, however, did not identify these as nuclides for which a fetal dose ratio greater than 1.0 (i.e. fetal dose higher than that for the mother) would occur. Other data show that for long term chronic intakes of 210 Pb that occurred prior to pregnancy (SSK (2004) tab. 4-2) the dose to the fetus may be more important. Newborn: breast milk transfer: Table 3 shows that breast milk transfer occurs for 210 Pb, 210 Po, 226 Ra, and 238 U, in this order of importance (for either chronic or acute intakes by the mother). The dose coefficients (infant dose/maternal dose) are all less than 1.0, with some being of the order of 10-3 -10-4 . Newborn: external exposure from maternal tissues: If the mother has an accumulated lung burden of radon progeny from current or previous exposures, there is the potential for some penetrating radiation dose to the newborn during breastfeeding or general contact. However, such doses are likely to be negligible. ii. Uranium Enrichment As noted above, the annual effective dose to workers involved in uranium conversion and enrichment activities is in a range from 0.4 to 1mSv. This dose is mainly due to external exposures. There is a probability that fetal exposures approaches 1 mSv. Accidental, acute intakes have been known to occur. The most likely situation would be an acute inhalation intake of uranium hexafluoride (UF6). In this instance, the dose to the fetus could occur from internal incorporation of uranium by the mother or from radionuclide transfer in breast milk. The available dose coefficients indicate that the fetal dose would generally be lower than the maternal dose in these cases. As noted above, concerns involving the chemical toxicity of the uranium and the fluoride species may be as or more significant than radiological concerns. iii. Fuel Fabrication In-utero: external and internal exposures: As noted above, the annual effective dose to workers involved in fuel fabrication activities is about 2 mSv and may involve dose from external gamma rays and intakes of airborne activities. It is thus possible for fetal doses to approach 1 mSv in these workplaces. In the case of mixed oxide (MOX) fuels, 20
  21. 21. considerations for both plutonium and uranium exposures should be made, and doses may generally be somewhat higher than in traditional fuel fabrication facilities. Newborn: breast milk transfer: Available data indicate that fetal doses from breast milk transfer of uranium will be a small fraction (of the order of 10-4 ) of the maternal dose, and probably not highly significant. Newborn: external exposure from maternal tissues: Doses to the newborn from maternally incorporated uranium should be very low, as the photon component of the decay scheme is very small. iv. Reactor Operation In-utero: external exposures: As noted above, average doses to workers during reactor operation can vary from a few mSv to more than 10 mSv, depending on the reactor type. These doses are predominantly due to external exposures, so it is clear that fetal doses approaching or exceeding 1 mSv are possible for the pregnant or potentially pregnant worker in such facilities. In-utero: radionuclide incorporation: Even though the exposures in reactor operation are primarily due to external exposures, significant internal exposures may occur, from a variety of possible radionuclides. The highest likelihood of intakes, however, occurs during equipment maintenance activities, where the workforce is predominantly male. As noted above, tritium intakes during HWR operation may be a significant component of worker exposure. Dose ratios (fetal dose/maternal dose) for intakes of tritium by all pathways vary between 1-2. Intakes of iodine, particularly 131 I, have been studied in various models involving the pregnant woman by a number of authors. Dose ratios vary between about 1 and 3, with dose to the fetal thyroid dominating the effective dose. Intakes are most likely only significant, however, in situations involving accidental intakes of iodine. Intakes of strontium isotopes may also contribute significantly to fetal doses; dose ratios for 90 Sr vary from less than 1 for chronic inhalation scenarios to values around 2.5 for acute ingestion, and ratios for 89 Sr vary from less than 1 for chronic inhalation scenarios to values as high as 7 for acute intakes. Newborn: breast milk transfer: Dose to the infant from ingestion of tritium as tritiated water is higher than the dose to the mother (ratio of 1.2), and for 131 I is considerably higher (around 2.5). Dose ratios for strontium isotopes are generally less than 1 for breast milk intakes. Newborn: external exposure from maternal tissues: Beta emitters in maternal tissues, such as tritium and strontium, will not contribute any external dose to the newborn. Annex C of ICRP 95 shows that external doses to the newborn from gamma emitters, including 131 I and 137 Cs, are much lower than internal doses from breast milk intakes. For inhalation of insoluble forms of 60 Co, however, the dose from external irradiation of the infant are about a factor of 3 higher than doses from milk ingestion. 21
  22. 22. v. Fuel Reprocessing Exposures during fuel reprocessing are more complex in general, involving both internal and external exposure pathways, from many different radionuclides. There may be significant differences in the kinds and levels of exposure between the various types of fabrication facilities in different countries. As noted above, the average annual effective dose to monitored workers is about 2.8 mSv. The contributions of internal and external doses to this total are not well known. It is also believed that the workforce is predominantly male. It is difficult to give a detailed analysis of the pathways important to the developing infant in this category, but it is clear that the doses to the embryo/fetus or newborn for pregnant women exposed could be significant. b. Medical Uses As noted above, the worker population in the medical area has many more female workers than in other professions involving the use of ionizing radiation. The proportion of the workforce may exceed 50%, although exact numbers are difficult to find. Medical uses are very diverse, and are considered here in three broad categories. 1. Medical Radiology (diagnostic and therapeutic) Medical radiology, whether involving diagnostic or therapeutic sources, involves only external sources of exposure to the radiation worker. Diagnostic radiology practice is discussed in section C2, above, and includes a variety of sources. Practices including standard film and digital radiography, computed tomography, mammography, and radiography in dentistry are associated with generally low routine radiation doses to the occupational workers. These annual doses are generally below 1 mSv and in many cases are not measurable. In radiotherapy as well, typical staff doses are below 1 mSv under normal circumstances, although some radiographers, radiotherapists, technicians and others may receive average annual doses exceeding 1 mSv. Interventional diagnostic radiography, however, includes procedures that may expose the staff to more significant dose rates, due to the need for persons to be present in the room where continuous or semi-continuous radiation sources are being operated. With careful attention to radiation protection practices, doses may be maintained at a reasonable level, but if protective measures are not well practiced, doses exceeding 20 mSv have been recorded. The declared pregnant worker in general should not participate in interventional procedures after the discovery of pregnancy. In many situations, however, it is clear that individual fetal doses for some radiology staff may approach 1 mSv, and should be carefully monitored. 2. Nuclear Medicine (diagnostic and therapeutic) As noted above, although the possible exposure pathways in nuclear medicine are many, the exposures to the staff in practice are dominated by the external exposure to gamma and beta radiation from handling the administered radiopharmaceuticals. Annual doses may approach 5 mSv (principally from 99m Tc), with the highest doses being received by the individuals directly involved in the administration of radiopharmaceuticals to patients. Staff in the 22
  23. 23. radiopharmacy, however, may often receive much higher doses on a regular basis. Administration of therapeutic levels of beta emitting nuclides or pharmacy preparation of this level of activity may result in significant local doses to the extremities. All staff in nuclear medicine have the potential to be exposed to radiation sources that can deliver 1 mSv to the fetus during gestation. It is notable that at the present time, there is a significant increase in the use of positron emitting radionuclides (principally 18 F as 18 FDG) in positron emission tomography (PET) and in the installation of PET/CT devices in many hospitals. Although average worker doses may not increase significantly, the number of workers exposed, and thus the collective dose to this segment of the radiation worker population, may be expected to increase in the near future, and the proportion of worker dose due to 18 F exposures may also increase. The potential for intake of radioactive materials in the nuclear medicine clinic and even in the radiopharmacy is generally low, under normal conditions with good radiation safety practice. An important exception is the inhalation of 131 I in volatile forms. 131 I as sodium iodide (NaI) is administered directly to patients for the treatment of hyperthyroidism and thyroid cancer. It is not uncommon for the nuclear medicine technologist to have measurable uptakes of 131 I in their thyroids after such administrations. There is also the possibility of 131 I incorporation by nursing staff due to 131 I exhalation by patients. 131 I is also labeled to a number of compounds for diagnostic and therapeutic purposes, and small amounts of free 131 I may be inhaled in these applications as well. 131 I freely crosses the placenta and, after about 11 weeks of gestation, is taken up by the fetal thyroid, which can receive a very large radiation dose from small amounts of 131 I uptake (Watson 1992)). Staff working with 131 I should thus be vigilant regarding exposures during pregnancy. Should nuclear medicine technologists that are pregnant or breast feeding have uptakes of radioactive material from the nuclear medicine clinic, there is a large body of literature discussing fetal uptake and dose models and breast milk uptake and excretion of radiopharmaceuticals in nuclear medicine patients (e.g. Stabin and Breitz, 2000) that can be useful in guidance. 3. Biomedical Research Biomedical research is involved with a number of radiolabeled tracers in a variety of applications. The majority of the radionuclides used are only beta emitters, although some beta/gamma emitters are in use. The levels of activity are typically low during routine practice, although periodic preparation of laboratory stock solutions may require manipulation of higher levels and concentrations of activity. As noted above, staff doses are typically low, around 1 mSv. However, if intakes of some of these compounds should occur, the intake may result in significant potential doses to the fetus as some elements, notably calcium and phosphorous have fetal/maternal dose ratios greatly exceeding 1. Tritiated and 14 C labeled organic compounds and 35 S also have in utero fetal/maternal dose ratios exceeding 1. Also, the breast milk transfer of calcium is significant, and the fetal/maternal dose ratio is around 2.5. c. Industrial Uses 23
  24. 24. Doses to workers in this industry are mostly due to external exposures. Average annual doses vary from around 1-3 mSv. In industries involved with applications of luminous materials (including 3 H and 147 Pm), and materials for smoke detectors (241 Am) intakes of radioactive material may occur as well. Special case: Radionuclide Production In radionuclide production, average annual doses are around 3 mSv, for the measurably monitored workers. Individual intakes may be higher, as some values as high as 10 mSv have been noted. In this application, both external and internal pathways will be quite important. The industry also contains a significant number of female workers. Few data are available, however, on the magnitude and frequency of exposures with the various radionuclides produced. The identity of the nuclides of important to industry also changes frequently. Considerable attention has been given by some investigators to 131 I external exposures and intakes. Significant intakes of 131 I have been recorded during in-vivo counting and in-vitro bioassay, with dose reconstructions performed. Other radionuclides will certainly present significant potential for external and/or internal exposures to the embryo/fetus and newborn. The species produced in the greatest volumes currently are 99 Mo (for use in 99 Mo/99m Tc generator systems) and 18 F (for use as 18 FDG). The dosimetry of 99 Mo and 18 F are well established, but little data has been published on possible worker exposures to these nuclides, so it is difficult at this time to say more quantitatively. At the present time there is also a heightened interest in the production of new alpha emitters for nuclear medicine therapy, and the individual nuclides being considered are changing frequently. It is clear, however, that many different radionuclides are being produced in many centers, which include gamma, beta, and alpha emitters of various forms. These different species can certainly all potentially contribute significant doses to the fetus (of the order of 1 mSv) from any of the four pathways considered here (in-utero internal or external exposure, and exposure of the newborn from breast milk or maternally incorporated activity). d. Natural Sources (other than uranium mining/processing) Air crew: average annual doses to air crew vary from 1-5 mSv, depending on the length and altitude of their flights. The dose to the fetus is due to only external exposure from penetrating cosmic radiation. The exposure during gestation apparently can exceed the 1 mSv level if continuous participation in flight activity is maintained throughout pregnancy. A number of other activities may result in the exposure of workers to enhanced levels of radiation from natural sources of radiation and radioactivity, in general principally due to exposure to radon and its progeny. In these cases, the considerations regarding external and internal exposure of the embryo/fetus and newborn as discussed in the section above on uranium mining and processing would apply:  Coal mining – annual doses reported from a number of countries are between 1 and 10 mSv.  Phosphate mining – annual effective doses for various mines range from a few mSv to values as high as 70 mSv. 24
  25. 25.  Metal ore mines – reported annual doses vary from around 2 to as high as 20 mSv.  Rare earth extraction from monazite, processing of thorium ores – annual effective doses vary considerably, from very low levels to around 15 mSv.  Radon therapy spas and groundwater treatment facilities – reported annual doses vary from less than 0.5 to more than 5 mSv.  Cave guides and guides in archeological sites – in particular sites where underground radon concentrations are elevated, cave guides may, according to model predictions, receive annual effective doses ranging from a few up to nearly 100 mSv. Other industries involve exposures due to scales in pipes and vessels containing 226 Ra:  Oil and gas exploration – Annual doses range from values below 1 mSv to values representing a significant fraction of annual worker dose limits (20 mSv).  TiO2 pigment production – annual worker doses may vary from about 1-6 mSv. 2. Summary and conclusions The recommendations of the International Commission on Radiological Protection (ICRP) and the IAEA Basic Safety Standards (BSS) make clear that the embryo and fetus should in be regarded as a member of the public when considering the protection of female workers who are or may be pregnant. The BSS note that the embryo and fetus should be “afforded the same broad level of protection as required for members of the public”. There is a requirement that women who may enter controlled or supervised areas are provided with information on the risks of radiation exposure of the embryo and fetus and that they should be informed of the importance of early notification of pregnancy. Similar guidance is included in national legislation, recommendations and guidance in a number of countries. However, there are a number of issues that require clarification, particularly:  the extent to which radiation exposure of the embryo and fetus may occur before pregnancy is declared;  the potential for doses to the embryo and fetus to exceed doses to the mother for intakes of particular radionuclides; and  the extent of additional dose to the newborn child from radionuclides transferred in breast milk and other maternal contact after birth.  the exact period over which restrictions/recommendations should apply, i.e.: o limit to apply to dose received in one year, o limit to apply during the remaining of the pregnancy, o limit to apply during all of pregnancy, or o limit to apply during all of pregnancy and the first 6 moths after birth. It can be concluded that while the recommendations provided in the BSS are in general agreement with the international consensus and practice on approaches to the protection of the pregnant or potentially pregnant worker (as laid out in various documents of the ICRP and of several government bodies), and are adequate for the purpose that they were intended to serve. However, more specific guidance for implementation by the member states is needed on this subject. It is recommended that a document be prepared that extends 25
  26. 26. and clarifies previous advice in the context of the issues outlined above and considers the practical application of the advice for workers in different types of workplace (possibly a Radiation Safety Guide). The ICRP has published dose coefficients (Sv per Bq intake) for the embryo and fetus and newborn child, considering intakes by inhalation or ingestion during and before pregnancy and during breast-feeding. The dose coefficients for in utero exposures include contributions from photon irradiation from radionuclides in maternal tissues, and from radionuclides transferred to the embryo and fetus, including doses delivered postnatally. These dose coefficients show that for most radionuclides, doses to the offspring following exposures in utero or from ingestion of breast-milk will be substantially lower than doses to the mother. However, for a number of radionuclides, doses to the offspring can be similar or substantially greater than doses to the mother. This applies particularly to intakes during pregnancy of isotopes of phosphorus, calcium and, to a lesser extent, sulfur, iodine and radium, and isotopes of nickel for long term exposures preceding pregnancy. In order to identify the important potential routes of exposure for the pregnant worker, four broad categories of radiation workplace have been classified (see Tables 4 and 5). In the nuclear fuel cycle, in general, the workers receive external and internal exposures, and the workforce involved in these practices is mostly males. The workers involved in medical techniques, diagnostic and therapeutic, receive external and internal exposure of radiopharmaceuticals, in the medical field the number of female workers is predominant compared to males. In industrial uses, most of the doses come from external exposure, except for production of radioisotopes, where doses from internal exposure can be significant and also the number of female workers can be higher compared to the other practices in industries. For exposure to natural sources of radiation other than uranium (mining and processing) radon and its progeny are the main contributors to the effective dose, and these activities involve a significant number of female workers. 26
  27. 27. 3. Actions required at the international level The Consultant Group recommends: 1. that a technical document (working material) be drafted that clarifies how to implement the recommendations of the BSS and to gives guidance on how to protect female workers and their offspring (Consultant meeting, April 2006), 2. that a questionnaire be developed that queries member states regarding their practices with radioactive sources, external and internal exposure and the involvement of male/female workers (April-July 2006), 3. that a Technical Meeting be held with representatives of various member states to discuss the technical document (Oct-Nov 2006), and 4. that a Safety Guide be written based on the working material, results of the member state questionnaire responses and the outcome of the Technical Meeting (June 2007). B. References Doll R. and Wakeford R. (1997) Risk of childhood cancer from fetal irradiation. British J. Radiology 70, 130-139. GB Parliament (1999) The Ionising Radiation Regulations 1999. London, HMSO, SI (1999) 3232. Health and Safety Commission (2000) Work with Ionising Radiation Approved Code of Practice and Guidance, Sudbury, HSE Books, L121. Health Canada. 2000 Report on Occupational Radiation Exposures in Canada. Minister of Public Works and Government Services, Canada, 2000. www.hc-sc.gc.ca. ICRP (1991) 1990 Recommendations of the International Commission on Radiological Protection ICRP Publication 60. Annals of the ICRP 21 (1-3). ICRP (2000) Pregnancy and Medical Radiation. ICRP Publication 84. Annals of the ICRP 30 (1) Elsevier Sciences, Oxford. ICRP (2001) Doses to the embryo and fetus from intakes of radionuclides by the mother. ICRP Publication 88. Annals of the ICRP 31, (1-3). Elsevier Sciences, Oxford. ICRP (2003) Biological effects after prenatal irradiation (embryo and fetus). ICRP Publication 90. Annals of the ICRP 33, (1). Elsevier Sciences, Oxford. ICRP (2004) Doses to infants from ingestion of radionulcides in mothers’ milk. ICRP Publication 95. Annals of the ICRP 34 (3-4). Elsevier Sciences, Oxford. 27
  28. 28. ICRP (2005) Recommendations of the International Commission on Radiological Protection (draft: www.icrp.org). NRPB (2005) Guidance on the application of dose coefficients for the embryo and fetus from intakes of radionuclides by the mother. Doc. NRPB. 16 (2). SSK (2004) Radiological Protection of the Unborn Child: Recommendation of the Commission on Radiological Protection and Scientific Grounds. German version: http://www.ssk.de/werke/volltext/2004/ssk0415.pdf. Stabin M and Breitz H. Breast Milk Excretion Of Radiopharmaceuticals: Mechanisms, Findings, And Radiation Dosimetry. Continuing Medical Education Article, Journal of Nuclear Medicine, 41(5):863-873, 2000. UNSCEAR (2000) United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionising radiation. Report to the General Assembly with Annexes. Vol II, United Nations, New York. Watson EE. Radiation Absorbed Dose to the Human Fetal Thyroid. In: Fifth International Radiopharmaceutical Dosimetry Symposium. Oak Ridge, Tennessee: Oak Ridge Associated Universities, pp 179-187, 1992. 28
  29. 29. Table 1. Ratios of fetal dose coefficientsa to corresponding adult dose coefficients for radionuclide ingestion by pregnant workersb (Table from NRPB, 2005.) Radionuclide Ratio, for intake time, weeks: 0c 5 10 15 25 35 3 H (water) 1.3 1.4 2.0 1.9 1.8 1.4 3 H (organic) 1.4 1.6 1.8 1.8 1.5 0.9 14 C 1.4 1.6 1.7 1.6 1.4 0.7 22 Na 1.1 1.1 1.1 1.1 1.2 1.0 32 P 0.7 2.9 10 11 13 14 33 P 3.5 10 23 24 25 18 35 S (organic) 1.7 2.0 2.2 2.2 2.1 1.8 35 S (inorganic) 0.9 1.1 1.2 1.2 1.1 1.3 45 Ca 0.6 1.5 10 15 16 12 47 Ca 0.4 0.4 5.0 5.9 6.3 6.4 59 Fe 0.8 0.8 0.8 1.0 1.5 1.3 65 Zn 1.2 1.2 1.2 1.2 1.1 0.9 75 Se 0.9 1.0 1.1 1.1 1.1 1.0 89 Sr 0.1 0.4 3.4 5.0 7.1 6.2 90 Sr 0.1 0.2 0.7 1.4 2.3 2.5 99m Tc 0.1 0.3 0.9 1.1 1.2 1.0 131m Te 0.3 0.3 0.3 0.5 1.1 1.7 125 I -d 0.1 0.1 0.4 0.9 1.3 131 Ie - - - 0.5 1.5 2.7 132 I 0.2 0.1 0.1 0.6 1.4 2.1 224 Ra 0.2 0.2 3.5 4.0 4.3 5.4 226 Ra - 0.1 0.8 1.3 1.8 1.3 228 Ra - - 0.1 0.2 0.5 1.2 a Committed effective doses. b Ratios are for single intakes at the times shown. Radionuclides included have values > 1 for intakes at one or more of the times considered. Values > 2 are shown in bold type. c Intake at around the time of conception. d Values < 0.05. e Ratios for 133 I and 135 I are similar to values for 131 I and exceed 1 at 25 weeks and 35 weeks. 29
  30. 30. Table 2. Ratios of fetal dose coefficientsa to corresponding adult dose coefficients for radionuclide inhalation by pregnant workersb (Table from NRPB, 2005.) Radionuclide(c) Ratio, for intake time, weeks: 0(d) 5 10 15 25 35 3 H [water vapour] (V) 1.3 1.4 2.0 1.9 1.8 1.4 3 H [organic vapours] (V) 1.4 1.6 1.9 1.8 1.6 0.9 14 C [vapour] (V) 1.4 1.6 1.7 1.7 1.4 0.7 32 P (F) 0.9 3.5 13 14 16 17 32 P (M) 0.3 1.1 3.8 4.1 4.9 5.0 33 P (F) 3.3 9.3 21 23 23 17 33 P (M) 0.3 0.8 1.9 2.0 2.0 1.5 35 S (F) 0.9 1.0 1.2 1.1 1.1 1.3 35 S [SO2] (V) 1.0 1.2 1.3 1.3 1.3 1.5 45 Ca (M) 0.2 0.4 1.8 2.5 2.7 1.8 47 Ca (M) 0.1 0.1 1.8 2.1 2.1 2.3 75 Se (F) 1.0 1.0 1.1 1.1 1.2 1.0 89 Sr (F) 0.3 0.7 5.9 7.9 8.8 7.9 90 Sr (F) 0.1 0.1 0.7 1.1 1.4 1.5 99m Tc (F) 0.2 0.3 1.0 1.2 1.3 1.1 131m Te [vapour] (F) 0.2 0.2 0.2 0.6 1.5 2.6 125 I(f) -(e) 0.1 0.1 0.4 0.9 1.3 131 I(f,g) - - - 0.6 1.6 2.8 132 I(f) 0.1 0.1 0.1 0.4 1.0 1.5 a Committed effective doses b Ratios are for single intakes at the times shown. Radionuclides included have values > 1 for intakes at one or more of the times considered. Values > 2 are shown in bold type. c Information in parentheses for each radionuclide relates to absorption from the respiratory tract and specific chemical forms. Only the chemical forms considered in ICRP Publication 68 (1994) for which ratios are greater than one are included in the Table. ICRP specifies default values for the rate of absorption of radionuclides to blood following deposition in particulate form: F (fast), M (moderate) and S (slow). For intakes as the gases and vapours considered in this table [noted in square brackets] absorption to blood is assumed to be either Type F or Type V (very fast, ie, complete and instantaneous). d Intake at around the time of conception. e Values < 0.05. f Ratios for isotopes of iodine apply to both elemental iodine vapour (Type F) and Type F particulate forms of iodine. g Ratios for 133 I and 135 I are similar to values for 131 I and exceed 1 at 25 weeks and 35 weeks. 30
  31. 31. Table 3. Ratios of infant dose to reference adult committed dose, considering transfer to milk after acute intake by the mother at one week after birtha (Table from ICRP, 2004.) Radionuclideb Ratio, for intake by: Inhalationc Ingestion 3 H (HTO)d 1.2 (V) 1.2 3 H (OBT)e 0.87 (V) 0.84 14 C (organic) 0.61 (V) 0.61 22 Na 0.36 (F) 0.42 28 Mg 0.24, 0.05 (F,M) 0.10 32 P 0.86, 0.13 (F,M) 0.70 35 S (organic) - 0.45 42 K 0.04 (F) 0.03 45 Ca 0.18 (M) 2.4 59 Fe 0.01 (M) 0.04 60 Co 0.18 (M) 0.63 63 Ni 0.02 (M) 0.04 65 Zn 0.11 (M) 0.28 75 Se 1.4 (F) 1.4 90 Sr 0.14 (M) 0.56 95 Zr 5 x 10-3 (M) 5 x 10-3 95 Nb 2 x 10-3 (M) 1 x 10-3 99 Mo 5 x 10-4 (M) 0.02 99m Tc 0.10 (M) 0.91 106 Ru 0.01 (M) 0.03 110m Ag 0.06 (M) 0.11 125 Sb 9 x 10-3 (M) 0.05 127m Te 5 x 10-3 (M) 0.05 131 I 2.5 (F,V) 2.5 137 Cs 0.28 (F) 0.29 133 Ba 0.02 (M) 0.08 144 Ce 5 x 10-3 (M) 3 x 10-4 210 Pb 0.11 (M) 0.38 210 Po 0.02 (M) 0.44 226 Ra 4 x 10-3 (M) 0.10 232 Th 4 x 10-4 (M) 6 x 10-4 238 U 4 x 10-4 (M) 8 x 10-3 237 Np 5 x 10-4 (M) 8 x 10-4 239 Pu 3 x 10-4 (M) 4 x 10-4 241 Am 3 x 10-4 (M) 5 x 10-4 242 Cm 3 x 10-4 (M) 1 x 10-3 a Intake by member of the public; reference adult dose coefficients from Publication 72 (ICRP, 1996). b Selected from radionuclides considered in this report: see Table 5.1. c Default absorption Type (ICRP, 1996) in brackets; that is, F (fast) or M (moderate) for inhaled particles. V applies to complete and rapid absorption of vapours. d HTO = tritiated water. e OBT = organically-bound tritium. 31
  32. 32. Table 4: Typical annual doses received in occupationally exposed workers (UNSCEAR 2000 + IAEA 2005*) Worker population Typical average annual exposures (mSv/a)a Type of Exposure Nuclear Fuel Cycle Uranium Mining and Processing Predominantly male 5 Internal and external sources Uranium Enrichment Predominantly male 1 Predominantly external sources Fuel Fabrication Predominantly male 2 Internal and external sources Reactor Operation Both genders 2.7 Internal and external sources Fuel Reprocessing Predominantly male 2.8 Internal and external sources Medical Uses Medical Radiology diagnostic and therapeutic Predominantly female <1-20 Predominantly external sources Nuclear Medicine diagnostic and therapeutic Predominantly female 5 Predominantly external sources Biomedical Research Both genders 1 Internal and external sources Industrial Uses General Predominantly male 0.3-3 Predominantly external sources Radionuclide Production Both genders 3 Internal and external sources Natural Sources * (other than uranium mining/processing) Air crew Both genders 1 - 5 External sources Coal mining Predominantly male 1 – 10 Internal and external sources Phosphate mining Predominantly male few – 70 Internal and external sources Metal ore mines Predominantly male 2 – 20 Internal and external sources Rare earth extraction from monazite Predominantly male very low – 15 Internal and external sources Processing of thorium ores Predominantly male very low – 15 Internal and external sources Radon therapy spas and groundwater treatment facilities Both genders 0.5 – 5 Internal and external sources Cave guides and guides in archeological sites Both genders few – 100 Internal and external sources a – annual effective dose for measurably exposed workers 32
  33. 33. Table 5: Potential for exposure of the embryo/fetus and newborn* In-utero Newborn External exposures Radionuclide incorporation Breast milk transfer External exposure from maternal tissues Nuclear Fuel Cycle Uranium Mining and Processing ++ ++ mc mc Uranium Enrichment mc mc mc mc Fuel Fabrication + + mc mc Reactor Operation ++ +++ ++ + Fuel Reprocessing ++ + ++ ++ Medical Uses Medical Radiology diagnostic and therapeutic +++ mc mc mc Nuclear Medicine diagnostic and therapeutic ++ + + mc Biomedical Research mc ++ + + Industrial Uses General ++ mc mc mc Radionuclide Production +++ +++ +++ +++ Natural Sources (other than uranium mining/processing) Air crew ++ mc mc mc Coal mining ++ ++ mc mc Phosphate mining ++ ++ mc mc Metal ore mines ++ ++ mc mc Rare earth extraction from monazite ++ ++ mc mc Processing of thorium ores ++ ++ mc mc Radon therapy spas and groundwater treatment facilities ++ ++ mc mc Cave guides and guides in archeological sites ++ ++ mc mc * (mc) minor concern (generally below 1 mSv), (+) could approach 1 mSv, (++) could exceed 1 mSv (++ +), could greatly exceed 1 mSv 33
  34. 34. F. CONTRIBUTORS TO DRAFTING AND REVIEW Ms. D. Rabelo de Melo National Nuclear Energy Commission (CNEN). Instituto de Radioproteçao e Dosimetria.. Departamento de Monitoracao Individual. Rio De Janeiro. Brazil Mr. P. Berard CEA DSM LABM. France Mr. D. Nosske. Bundesamt für Strahlenschutz Fachbereich Strahlenschutz und Gesundheit . Germany Mr. J. Harrison. Health Protection Agency. Centre for Radiation, Chemical and Environmental Hazards. UK. Mr. M. Stabin. Department of Radiology and Radiological Sciences. Vanderbilt University. USA Mr. R. Cruz Suárez. Occupational Radiation Protection Unit. Division of Radiation, Transport and Waste Safety. Department of Nuclear Safety and Security. IAEA. 34

×