Salient features of the forthcoming ICRP recommendations-2007

1. Salient features of the forthcoming ICRP recommendations-2007 Dr. Pushparaja Ex. Head, Radiation Hazards Control Section, RSSD, BARC (Based on the ICRP approved draft recommendations -2007 (13/2/2007) www.radsafetyinfo.com

2. Since 1990 Recommendations • New biological and physical information • New trends in setting and presentation of radiation protection standards • Societal changes leading to more emphasis on the protection of individuals and stakeholders in the management of radiological risk • More emphasis on the radiological protection of non-human species.

3. The major features • Updating the radiation and tissue weighting factors and radiation detriment • Maintaining the commission’s three fundamental principles: justification, optimization and application of dose limits • Abandoning the process-based approach and moving to situation-based approach and applying the same source-related principles to all controllable exposure situations-planned, emergency and existing exposure situations.

4. Continued…. • Maintaining the existing individual dose limits for effective dose and equivalent dose from all regulated sources. These represent the maximum dose that would be accepted in planned situations by the regulators. • Principle of optimization is applicable to all exposure situations with restrictions on individual doses (dose constraints) for planned exposures and reference levels for emergency and existing exposure situations. • Developing a framework for radiological protection of non-human species.

5. Source is any physical quantity or procedure that results in potentially quantifiable radiation dose to a person or group of persons.

6. Types of harmful effects(ICRP-99, 2006) Radiological protection deals with two types of harmful effects: • Tissue reactions (deterministic effects) • Incidence of cancer or hereditary effects (stochastic effects)

7. For protection, action at Source Environmental pathways Exposure Dose to individuals

8. The aims of the recommendations To contribute to an appropriate level of protection for people and the environment against the detrimental effects of radiation exposure without unduly limiting desirable human endeavours and actions that may be associated with such exposures. The recommendations are based on the scientific knowledge and expert judgements.

9. Objectives of the system radiological protection • For humans: To mange and control exposures to ionizing radiation so that tissue reactions are prevented and risks of cancer and heritable effects are minimized. • For environment: Control exposures to ensure negligible impact

10. Basis The system of protection of humans is based on the use of: • Reference anatomical and physiological models for assessment of radiation doses • Biological studies at the molecular and cellular level • Experimental animal studies on mechanisms of carcinogenesis and heredity • Epidemiological studies

11. Principles of radiological protection The two principles which are source-related and applicable to all situations are: • Justification – to achieve an individual or societal benefit that is higher than the detriment it causes. • Optimization of protection – to maximize the margin of benefit over harm; ALARA.

12. Continued… • Application of dose limits Individual-related, and applies to planned exposure situations. Total dose should not exceed the limits. Not applicable to medial exposures, public exposures in emergency situations and to existing exposure situations. The limits are same as those given in ICRP-60, 1991.

13. The scope of the recommendations Applies to all radiation sources, both natural and man-made, and controllable exposures from any source or sources regardless of its size and origin. Also applies to all radiation exposure situations.

14. System of radiation protection of humans Commission moves from the earlier process based approach to the following three types to address all conceivable types of exposure situations: • Planned • Emergency, and • Existing exposure

15. Planned Exposure situations Radiological protection can be planned in advance, before exposure occurs-magnitude and extent of the exposure can be reasonably predicted, cover medical exposure of patients, comforters and carers, all categories of exposure can occur, also covers potential exposures, which may result from deviations from the normal operating conditions, safety and security of sources is the issue of concern

16. Emergency exposure situations • Unexpected situations requiring urgent protective actions to be implemented. • Exposure scenario is complex • Response actions can be planned to some extent • Actual emergency situations are unpredictable • To be optimized using a chosen reference levels (20-100 mSv band) • Overall dose from the possible multiple pathways, with no protection action employed is called as Projected dose (ICRP-101, 2006) • Protection strategy to reduce residual dose level below the reference dose • Integrate radiation emergency response plan into all-hazards emergency management program

17. Existing exposure situations Type of existing exposure situations where exposures can be high enough to warrant radiological protective actions are: • Radon in dwellings/workplaces • NORM residues • Residues in the environment due to emissions from past operations • Contaminated territories resulting from accidents

18. Linear non-threshold model • Commission assumes that at doses below 100 mSv in a year, the increase in the incidents of stochastic effects with a small probability and in proportion to the increase in radiation dose over the background dose and hence, the LNT model is the best practical approach for managing risk from low dose radiation exposure. • ICRP recommends LNT model combined with a dose and dose arte effectiveness factor (DDREF) for extrapolation from higher doses for radiological protection at low dose and low dose rates (ICRP-99, 2006).

19. Levels of radiological protection • An individual exposed to several sources; exposures identified and quantified; include all exposures from regulated sources - called individual-related approach. • Considering the exposures of all the individuals exposed by each regulated source – source-related approach. Appropriate level of protection is achieved by optimization using dose constraints and reference levels

20. Categories of exposures • Occupational exposure Operating management and Licensee responsible for the safety • Public exposures All exposures other than occupational and medical exposures incurred as a result of a range of radiation sources, natural and man-made • Medical exposures of patients, comforters and carers (separate guidance provided)

21. Exposed individuals • Workers Has recognized rights and duties in relation to occupational radiological protection. Pregnant workers not to avoid work, can work in designated areas; should not be involved in emergency actions involving high radiation doses; treated like members of the public. Additional equivalent dose to the fetus would not exceed 1 mSv during the reminder of the pregnancy.

22. Continued…. • Members of the public A large number of different natural and man-made sources is contributing; Dose restrictions are applied to the mean dose in the appropriate critical group. Critical group concept is replaced by “The representative person” (Pub: 101, 2006); Typical habits of individuals in a representative group in the most exposed, are used.

23. Continued… • Patients, comforters, carers Individuals, who receives an exposure from diagnostic, therapeutic and screening procedures, which are justified and optimized. Dose limits/constraints not applicable. To use diagnostic reference levels. (ICRP-73, 1996)

24. Dose constraints (in planned exposure situations) and Reference levels (in emergency and existing situations) are used for protection of members of the public or workers from a single source in all exposure situations (Source-related restriction). These are used in conjunction with optimization of protection to assure ALARA

25. Dose constraint/Reference levels • Dose constraints can be defined as a level of dose above which it is unlikely that protection is optimized for a give source and therefore action must always be taken to bring the level of dose below the constraint. • Reference levels represent the dose or risk above which it is judged to be inappropriate to plan to allow exposures to occur and below which optimization should be implemented.

26. Due to multiplicity of the sources, sole reliance on source-related restrictions may not provide the required level of protection. Restriction on the sum of the doses from the sources is required; this individual-related restriction is called – Dose Limit

27. Optimization • It is the principle of protection with a restriction on individual dose is the central to the system of protection applying to all the three exposure situations, planned, emergency and existing. Meaning to: To keep likelihood of incurring exposures, the number of people exposed and the magnitude of individual doses ALARA below the dose constraints or reference levels, taking into account economic and societal factors.

28. Optimized protection is the result of an evaluation, which balances the detriment (economic, human, societal, political) and the resources available for protection of individuals. Best option need not necessarily the one with the lowest dose.

30. Uncertainties • In view of the uncertainties in the estimate of detriment and the value of tissue weighting factors, the ICRP considers it appropriate to use age and sex averaged tissue weighting factors and numerical risk estimates, for radiological protection purposes. • For the purpose of retrospective evaluation of radiation related risks such as epidemiological evaluations, and for the evaluation of exposure risk of over-exposed cases, age and sex-specific data should be used.

31. Sex averaging It is useful to determine a single value of effective dose for both sexes. The tissue weighting factors are sex averaged values and are valid for the male and female breast, testes and ovaries taken together in the value for the gonads, and other organs and tissues with assigned explicit Wt values. The effective dose is computed from the weighting factor multiplied by the arithmetic mean of the equivalent dose assessed for organ or tissue T of the male, and female including the remainder tissues.

32. Nominal risk estimates ICRP’s risk estimates are called nominal because they relate to the exposure of a nominal population of females and males with a typical age distribution and are computed by averaging over age groups and both sexes. Effective dose is the dosimetric quantity recommended for radiological protection. Use absorbed dose in known exposure scenarios.

33. Nominal Risk Coefficients Risk of hereditary effects continues to be included in the Commission’s system of radiological protection. Post 1990 human and animal data on the quantitative aspects of radiation-induced germ cell mutation and the fundamental understanding of the human genetic diseases indicated that the risk of heritable disease was overestimated in the past.

34. Continued… The newly estimated hereditary risks employing human and mouse studies and in view of the lack of clear evidence in human of germ line mutations caused by radiation (in demonstrable genetic effects in offspring), works out to be 0.2% per Sv. This value relates to continuous low dose-rate exposure over these two generations (UNSCEAR-2001: NAS/NRC-2006) The judged value for tissue weighting factor for gonads is considerably reduced.

35. Detriment – adjusted nominal risk coefficients for cancer and hereditary effects • Sex-averaged nominal risk coefficients for cancer involves the estimation of normal risks for different organs and tissues followed by adjustment of these risks for lethality and quality of life and the derivation of a set of site-specific values of relative detriment. • This includes heritable effects from gonadal exposure. These relative detriments form the basis for the new tissue weighting factors.

36. Continued………. The ICRP detriment was based on fatal cancer risk weighted for non-fatal cancer, relative life lost for fatal cancers and life impairment for non-fatal cancers.

37. Radiation type Photons Electrons & Muons Protons & Charged Pions Alpha, FF & Heavy Ions Neutrons (Continuous function of neutron energy) Radiation WeightingFactor 1 1 2 20 2 to 20 Radiation weighting factors(ICRP-92, 2003)

39. Tissue Bone marrow, colon, lung, Stomach, Breast, Remainders (13 organs/tissues) Gonads Bladder, Oesophagus, Liver, Thyroid Bone surface, Brain, Salivary glands, Skin WT 0.12 0.08 0.04 0.01 Recommended Tissue Weighting Factors

40. Publication 60 Whole population Cancer 6.0 Heritable 1.3 Total 7.3 Adult Cancer 4.8 Heritable 0.8 Total 5.6 ICRP-2007 Whole population Ca ncer 5.5 Heritable 0.2 Total 6.0 Adult Cancer 4.1 Heritable 0.1 Total 4.0 Nominal Risk Coefficients (% per Sv)

41. Collective dose concept • Collective dose takes into account the group of persons exposed and the period of exposure from a source. The collective effective dose (man sievert) is retained as an instrument for optimization purpose only, for comparing radiological technologies and protection procedures, not for risk projections. Commission recommends avoidance of computation of cancer deaths using collective doses involving trivial exposures over extended periods to large populations. The dose calculations should have limiting conditions of the dose range and the time period (ICRP-77/81 (1998/2000).

42. Continued…. Each exposure situation must be carefully analyzed to identify the individual characteristics and exposure parameters that best describe the exposure distribution among concerned population. In the decision taking process, less weight should be given to very low doses and to doses received in the distant future since the doses and sizes of exposed population becomes increasingly uncertain as time increases.

43. ICRP defined bands of Dose constraints/ Reference levels • 0.01 to 1 mSv Benefit to society; Planned operation of practices with marginal increase in exposures above natural background; Provides rigorous level of protection by direct action on the source; periodic checks. Ex: Constraints set for public exposure.

44. Continued… • 1 mSv – 20 mSv Individuals get direct benefit from an exposure situation not necessarily from the exposure; Individual monitoring, training; constraints set for occupational exposure in planned situations, exposure involving high levels of natural background radiation; Exposure control by action at the source or at the exposure pathways. Ex: Constraints set for Occupational exposure in planned situations; Reference levels for radon in dwellings

45. Continued…. • 20 to 100 mSv Projected dose over a time period; Total dose from all the sources; Source can not be controlled; extreme situations where actions taken to reduce exposures are disruptive such as in radiological emergency; acute exposures not expected to be repeated. Important: Selection of an appropriate value for the reference level is the necessary and important for protection, whatever the situation.

47. Medical exposure of patients Medical exposure covers: • The exposure of individuals for diagnostic, fluoroscopically guided interventional, and therapeutic purposes • Family members, friends supporting and comforting patients • Volunteers in biomedical research

48. Ensure that • Doses to patient dose to be commensurate with the medical purpose • Avoid unnecessary / unproductive doses in intervention procedures (ICRP-85/87/93; 2000,2000, 2003) • Avoid exposure of healthy tissues in radiotherapy (ICRP-44, 1985) • ICRP-73, 1996 recommendations remain valid, Also: the documents SG-2, 2001 & ICRP-2007.

49. Radiation effects in the embryo and fetus • At doses below 100 mGy of low LET radiation • Lethal effects of irradiation in the pre-implantation period of embryonic development is very infrequent. • Radio-sensitivity maximum during the period of major organogenesis • Animal data indicates a true dose threshold of 100 mGy for the induction of malformation. • A-bomb survivor data supports a true dose threshold of at least 300 mGy for severe mental retardation after irradiation. Any effect on IQ following in-utero doses under 100 mGy is of no practical significance (ICRP-90, 2003)

50. Unjustified medical procedures • Addition of activity in commodities and consumer products • Radiological exposures for any purpose without any clinical evaluation of the images / clinical indication • Mass screening of population groups unless for detecting diseases and its control if detected.