Perspectives on tolerability and reasonableness.

Judgements on tolerability and reasonableness are central to the optimisation of protection. There are currently several international developments regarding these key considerations which will contribute to the review and evolution of the system of radiological protection. The IRPA15 International Congress brought together the principal issues currently under discussion, and the outcome of these discussions is presented.

Translating science into recommendations: the development of NCRP Report No. 180.

The development of new recommendations for radiological protection is a complex process of translating scientific knowledge of radiation risks into a coherent system for protection, using experience and ethical values. From 2014 to 2019, the US National Council on Radiation Protection and Measurements (NCRP) engaged in the development of updated recommendations to replace those previously published in 1993. This process included considering the experiences gained with implementation of the NCRP recommendations, and the recommendations of the International Commission on Radiological Protection. The new recommendations, now published as NCRP Report No. 180, go beyond the previous recommendations of the ICRP and NCRP, providing new approaches to emergency response and protection of the environment, covering additional topics not previously addressed in medical exposure. The system of protection continues to rely on justification of actions, optimisation of protection, and use of individual dose criteria to achieve the best protection for each exposure situation. For the first time in general recommendations, ethical values are discussed, and their use in complex decision making to achieve sustainable and supportable decisions outlined. The importance of stakeholder engagement is highlighted, as is the relationship with a radiation protection and safety culture. This paper outlines some of the questions and considerations that were part of the development of NCRP Report No. 180.

NCRP Report no.180-management of exposure to ionizing radiation: NCRP radiation protection guidance for the United States.

NCRP Report No. 180, 'Management of Exposure to Ionizing Radiation: Radiation Protection Guidance for the United States (2018)' was developed by Council Committee 1. The report builds and expands upon previous recommendations of NCRP and ICRP, covering exposure to radiation and radioactive materials for five exposure categories: occupational, public, medical, emergency workers, and nonhuman biota. Actions to add, increase, reduce or remove a source of exposure to humans require justification. Optimisation of protection universally applies, taking into account societal, economic, and environmental factors; addressing all hazards, and striving for continuous improvement when it is reasonable to do so. Numeric protection criteria for management of dose to an individual for a given exposure situation are provided, and differ in some respects from ICRP. A specific numeric criterion is suitable to be designated as a regulatory dose limit only when the source of exposure is stable, characterised, and the responsible organisation has established an appropriate radiation control program in advance of source introduction. Medical exposure includes patients, comforters and caregivers of a patient, and voluntary participants in biomedical research. Emergency workers are a new exposure category; their exposure is treated separately from occupational, public or medical exposure, and numeric criteria are provided for deterministic and stochastic effects. For nonhuman biota, the focus is on population maintenance of the affected species, and a guideline is provided for when additional assessment may be necessary. In addition, the recommendations emphasise that: ethical principles support decision-making; stakeholder engagement is necessary in deciding suitable management of their radiation exposure; and a strong safety culture is intrinsic to effective radiation protection programs.

The new mandate and work of ICRP Committee 4.

Committee 4 of the International Commission on Radiological Protection (ICRP) is charged with the development of principles and recommendations on radiological protection of people and the environment in all exposure situations. For the term beginning in July 2017, the Committee has a total of 18 members from 12 countries. The programme of work includes a wide range of activities in five major thematic areas. The first is the consolidation and preparation of reports elaborating application of the system of protection in existing exposure situations. Second is the continuation of work on emergency exposure situations, and ICRP updates to recommendations in light of the accident at Fukushima Daiichi nuclear power plant. Third is examination of fundamentals of protection recommendations, including the ethical principles underlying the recommendations and application of those principles in practical decision making. Fourth is the new area of integration of protection of the environment into the system of protection. Finally, Committee 4 continues work to prepare specific topical reports on subjects in which additional information is useful to understand and apply the Commission's recommendations in particular circumstances.

Overview of ICRP Committee 4: application of the Commission's recommendations.

Committee 4 develops principles and recommendations on radiological protection of people in all exposure situations. The committee meeting in 2014 was hosted by GE Healthcare in Arlington Heights, IL, USA on 27 July-1 August 2014. The programme of work of Committee 4 encompasses several broad areas, including a series of reports covering various aspects of existing exposure situations, leading the efforts of the International Commission on Radiological Protection (ICRP) to update and elaborate recommendations in light of the accident at Fukushima Daiichi nuclear power plant for emergencies and living in contaminated areas, elaborating the underpinnings of the system of radiological protection, and developing focussed reports on specific topic areas in consultation with ICRP's special liaison organisations. Committee 4 has six active Task Groups working on naturally occurring radioactive material; cosmic radiation in aviation; updates of ICRP Publications 109 and 111; ethics of radiological protection; surface and near-surface disposal of solid radioactive waste; and exposures resulting from contaminated sites from past industrial, military, and nuclear activities. In addition, there is a Working Party on tolerability of risk, and ongoing work with the various special liaison organisations of ICRP.

Review of the ICRP system of protection: the approach to existing exposure situations.

The International Commission on Radiological Protection (ICRP) system of protection consists of existing, planned, and emergency exposure situations. With the 2007 Recommendations in ICRP Publication 103, a coherent approach has been established that emphasises the optimisation of protection with appropriate constraints or reference levels in each exposure situation. Existing exposure situations pose unique challenges because the source of exposure already exists, and it may not always be possible to control the source directly. This is the case for naturally occurring sources, which are ubiquitous in the environment and vary widely in the magnitude of exposures that may be received by individuals. Decisions on protection strategies must consider a graded, pragmatic, and flexible approach for dealing with exposure of members of the public, and those that may be occupationally exposed while working with naturally occurring sources. Although limits are not applicable, aspects of the management approach for planned exposure situations may be appropriate, depending upon the magnitude of exposures.

ICRP Publication 124: Protection of the Environment under Different Exposure Situations.

In this report, the Commission describes its framework for protection of the environment and how it should be applied within the Commission's system of protection. The report expands upon its objectives in relation to protection of the environment, in so far as it relates to the protection of animals and plants (biota) in their natural environment, and how these can be met by the use of Reference Animals and Plants (RAPs); their Derived Consideration Reference Levels (DCRLs), which relate radiation effects to doses over and above their normal local background natural radiation levels; and different potential pathways of exposure. The report explains the different types of exposure situations to which its recommendations apply; the key principles that are relevant to protection of the environment; and hence how reference values based on the use of DCRLs can be used to inform on the appropriate level of effort relevant to different exposure situations. Further recommendations are made with regard to how the Commission's recommendations can be implemented to satisfy different forms of environmental protection objectives, which may require the use of representative organisms specific to a site, and how these may be compared with the reference values. Additional information is also given with regard to, in particular, communication with other interested parties and stakeholders. Issues that may arise in relation to compliance are also discussed, and the final chapter discusses the overall implications of the Commission's work in this area to date. Appendices A and B provide some numerical information relating to the RAPs. Annex C considers various existing types of environmental protection legislation currently in place in relation to large industrial sites and practices, and the various ways in which wildlife are protected from various threats arising from such sites.

ICRP Publication 125: Radiological Protection in Security Screening.

The use of technologies to provide security screening for individuals and objects has been increasing rapidly, in keeping with the significant increase in security concerns worldwide. Within the spectrum of technologies, the use of ionizing radiation to provide backscatter and transmission screening capabilities has also increased. The Commission has previously made a number of statements related to the general topic of deliberate exposures of individuals in non-medical settings. This report provides advice on how the radiological protection principles recommended by the Commission should be applied within the context of security screening. More specifically, the principles of justification, optimisation of protection, and dose limitation for planned exposure situations are directly applicable to the use of ionising radiation in security screening. In addition, several specific topics are considered in this report, including the situation in which individuals may be exposed because they are concealed ('stowaways') in a cargo container or conveyance that may be subject to screening. The Commission continues to recommend that careful justification of screening should be considered before decisions are made to employ the technology. If a decision is made that its use is justified, the framework for protection as a planned exposure situation should be employed, including optimization of protection with the use of dose constraints and the appropriate provisions for authorisation and inspection.

ICRP, 123. Assessment of radiation exposure of astronauts in space. ICRP Publication 123.

During their occupational activities in space, astronauts are exposed to ionising radiation from natural radiation sources present in this environment. They are, however, not usually classified as being occupationally exposed in the sense of the general ICRP system for radiation protection of workers applied on Earth. The exposure assessment and risk-related approach described in this report is clearly restricted to the special situation in space, and should not be applied to any other exposure situation on Earth. The report describes the terms and methods used to assess the radiation exposure of astronauts, and provides data for the assessment of organ doses. Chapter 1 describes the specific situation of astronauts in space, and the differences in the radiation fields compared with those on Earth. In Chapter 2, the radiation fields in space are described in detail, including galactic cosmic radiation, radiation from the Sun and its special solar particle events, and the radiation belts surrounding the Earth. Chapter 3 deals with the quantities used in radiological protection, describing the Publication 103 (ICRP, 2007) system of dose quantities, and subsequently presenting the special approach for applications in space; due to the strong contribution of heavy ions in the radiation field, radiation weighting is based on the radiation quality factor, Q, instead of the radiation weighting factor, wR. In Chapter 4, the methods of fluence and dose measurement in space are described, including instrumentation for fluence measurements, radiation spectrometry, and area and individual monitoring. The use of biomarkers for the assessment of mission doses is also described. The methods of determining quantities describing the radiation fields within a spacecraft are given in Chapter 5. Radiation transport calculations are the most important tool. Some physical data used in radiation transport codes are presented, and the various codes used for calculations in high-energy radiation fields in space are described. Results of calculations and measurements of radiation fields in spacecraft are given. Some data for shielding possibilities are also presented. Chapter 6 addresses methods of determining mean absorbed doses and dose equivalents in organs and tissues of the human body. Calculated conversion coefficients of fluence to mean absorbed dose in an organ or tissue are given for heavy ions up to Z=28 for energies from 10 MeV/u to 100 GeV/u. For the same set of ions and ion energies, mean quality factors in organs and tissues are presented using, on the one hand, the Q(L) function defined in Publication 60 (ICRP, 1991), and, on the other hand, a Q function proposed by the National Aeronautics and Space Administration. Doses in the body obtained by measurements are compared with results from calculations, and biodosimetric measurements for the assessment of mission doses are also presented. In Chapter 7, operational measures are considered for assessment of the exposure of astronauts during space missions. This includes preflight mission design, area and individual monitoring during flights in space, and dose recording. The importance of the magnitude of uncertainties in dose assessment is considered. Annex A shows conversion coefficients and mean quality factors for protons, charged pions, neutrons, alpha particles, and heavy ions(2 < Z ≤2 8), and particle energies up to 100 GeV/u.

US NRC discussion of options to revise radiation protection recommendations.

The Nuclear Regulatory Commission (NRC) is continuing the process of engaging stakeholders on issues associated with possible changes to the radiation protection regulations contained in 10 CFR Part 20, and other parts of the NRC regulations, to increase alignment with international recommendations. The Commission is particularly seeking to explore implications, as appropriate and where scientifically justified, of greater alignment with the 2007 Recommendations of the International Commission for Radiological Protection. Other information from national and international sources is also being considered. Given that the NRC regulations provide adequate protection, the discussion has been focusing on discerning the benefits and burdens associated with revising the radiation protection regulatory framework. NRC, through three Federal Register Notices, has officially solicited comments on a series of key issues, and has conducted a series of facilitated workshops to encourage feedback from a wide range of stakeholders. The issues include the use of updated scientific methodologies and terminology, the occupational dose limits, and the use of the concepts of constraints in optimisation. NRC staff provided a policy paper with recommendations to the Commission on April 25, 2012 (NRC, 2012).

Tritium distribution and excretion following intratracheal instillation of glass microballoon fragments in rats.

The distribution and time course for tritium activity in Sprague-Dawley rats exposed to tritiated glass fragments by intratracheal instillation have been defined. Particles were deposited primarily in the pulmonary region, allowing for the measurement of long-term tritium dissolution and particle movement. The tritium activity of the body water and tissues was found to follow a three-compartment model where tritiated glass fragments provide a continuous input to the body water, and tritium was removed from the body according to the classical elimination pattern for HTO. The dissolution of tritium in vivo was found to be biphasic with exponential function half-times of 6.3 +/- 0.5 and 43 +/- 3 days, respectively. The glass fragments were removed from the pulmonary region slowly, with a half-time of 150 +/- 30 days. The resultant dose to the lung was three orders of magnitude greater than the dose to the body, and approx. 40 times greater than the dose incurred in the lung from the inhalation of a similar quantity of HTO. A theoretical urine tritium time course for the inhalation of glass fragments was found to resemble the typical HTO patterns for several months post-exposure. The similarity of tritiated glass and HTO urine activity will make the determination of the type of exposure difficult.