Risk evaluation and risk management in the field of ionizing and non-ionizing radiation

A. Slavchev*, M. Israel** - Sofia, Bulgaria

* National Centre of Radiobiology and Radiation Protection
** National Centre of Hygiene, Medical Ecology and Nutrition

Abstract

Medical irradiation with ionizing radiation is the greatest anthropological source of above-background irradiation of the European population (about 90%). Publications of ICRP, EC, Directive 97/43 EURATOM, etc. provide basic guidelines for control of the risk from ionizing radiation. The exposure of the general population to non-ionizing radiation is addressed by different compulsory and recommended standardization documents, such as those issued by ICNIRP, IEEE, etc. In order to respond to such uncertainties certain agencies and scientists recommend approaches based on concepts like Precautionary Principle, Prudent Avoidance and ALARA. The problems of ionizing and non-ionizing radiation risk communication and management could be managed by development of national programs with international support.

Introduction

The general population is extremely sensitive to ionizing radiation, particularly where levels are above the norm. Requests for information on the possible health effects of electromagnetic radiation (EMR), addressed by citizens to media and state authorities, are becoming more and more frequent.

The acceptance of exposure limits, depends on the risk perception and risk communication policies. Although the regulations and the exposure limits for adverse effects are based on the best presently proven scientific evidence, yet there are doubts due to uncertainty in the risk assessment process. A more complex form of uncertainty is associated with the possible existence of risk from long-term (chronic) exposure to low levels. As a principle, it is impossible to prove the absence of such hazards.

A serious problem in risk perception and risk communication emerges from the difference in developing standards for ionizing and non-ionizing radiation - the threshold approach for the non-ionizing, and the hypotheses for non-threshold effect for the others. The differences in national psychology and culture impede the development of universally applicable programs and methodologies for risk communication and management.

Risk and its subject

In trying to understand people's perception of risk, it is important to distinguish between a health hazard and a health risk. A hazard can be an object or a set of circumstances that can potentially harm a person's health. Risk is the likelihood, or probability, that a person will be harmed by a particular hazard. It incorporates the uncertainty and the seriousness of undesired consequences.

Risk in the general sense of the term includes three main steps: the risk assessment, risk perception and risk management, as is shown in [1]. The risk assessment is a complicated process that is not a topic of this paper. The factors that shape risk perception of individuals include basic societal values (e.g. traditions, customs) as well as previous experience with technological projects (e.g. dams, power plants). These factors may explain local concerns, possible biases or hidden assumptions. Careful attention to the social dimensions of any project allows policy makers and managers to make informed decisions as part of a thorough risk management program. Ultimately, risk management must take into account both measured and perceived risk to be effective.

The identification of problems and the scientific risk assessment of those problems are key steps to defining a successful risk management program. To respond to that assessment, such programs should incorporate actions and strategies, such as finding options, making decisions, implementing those decisions, and evaluating the process. These components are not independent, nor do they occur in a determined order. Rather, each element is driven by the urgency of the need for a decision, and the availability of information and resources. It is very important to improve management programs depending on the purpose of the problem. Different programs should be developed for a variety of purposes, such as: new technology, public concern, occupational exposures, risk communication programs. One example for such a program is the range of risk management options given by WHO for developing a communication program:

"Communication programs can be used to help people understand the issues, become involved in the process and make their own choices about what to do.

• Decision to take no formal action is an appropriate response in cases where the risk is considered negligible, or the evidence is insufficient to support formal actions. This response is often combined with watchful waiting: continuing to monitor the results of research and measurement and the decisions being made by standard-setters, regulators, and others.
• Research fills gaps in our knowledge, helps to identify problems, and allows for a better assessment of risk in the future.
• Cautionary approaches are policies and actions that individuals, organizations or governments take to minimize or avoid future health or environmental impacts. These can be a decision of an industry or other group to undertake voluntary self-regulation.
• Regulations are formal steps taken by government to limit both the occurrence and consequences of potentially risky events. Numeric standards may be imposed with defined ways to show compliance.
• Limiting exposure or banning the source of exposure all together are options to be used when the degree of certainty of harm is high. The degree of certainty and the severity of harm are two important factors in deciding the type of actions to be taken.
• Technical options can be considered during development of new technology, but should always be transparent for the benefit of the stakeholders. Options may include the consideration of the necessity to optimize for capacity and coverage, as well as the possibility of multiple and smaller sites as opposed to a single large site. Site sharing options should be made available.
• Mitigation involves making physical changes in the system to reduce exposure and, ultimately, risk. Mitigation may mean redesigning the system, installing shielding or introducing protective equipment.
• Compensation is sometimes offered in response to higher exposures in a workplace or environment. People may be willing to accept something of value in exchange for accepting increased exposure.

Risk management in the case of ionizing radiation

Medical sources of radiation are the greatest anthropogene factor for the artificial irradiation of the population (in Europe approximately 90%) but also one of the means significantly to reduce the negative effects of and by this, adequately to control (diminish) the risk. Generally seen the risk of the medical exposure to ionizing radiation encompasses the deterministic (with threshold dose values) and the stochastic (probability proportional to the radiation exposure) effects.

The risk degree depends on various factors: kind of radiation, characteristics of the object (tissue) irradiated, patient age (dynamics-variant), condition (physical, somatic, genetic predetermination), milieu (home, work), complexity and duration of the examination, techniques and so on.

Categorized by the International Commission on Radiation Protection (ICRP) in: acceptable, tolerable and unacceptable [2], the risk represents the basis for one of the fundamental postulates - the justification of the medical exposure. The justification namely implies the netto/benefit for the patient with reference to:

• diagnosis,
• care and treatment,
• final result for the patient,

and only when all this cannot be achieved by an alternative, patient-friendly method. Special attention is paid to prenatal status, children, pregnant, breast feeding women and others as well as healthy patients in scientific research.

Basic principles for the second postulate - the optimization are:

• ALARA,
• informed consent,
• prudent avoidance,
• independence (clinical freedom), accountability, decentralization,
• preserving good medical traditions.

As a result of the scientific achievements in medicine (risk from ionizing radiation when used for diagnostic and therapeutic purposes) and the rapid progress in the medical technology and information in recent years as well as the deeper consciousness of the interrelation "technology-patient" and the ever increasing attention and care for the health and comfort of the patient, aiming at a steady improvement of the quality of life criteria/ protocols for justification and realization of good medical practices and standards/norms for image optimization (equipment, protection, methodology, etc.) have been elaborated and then approved by the European Commission and in the form of the Directives 96/29 and 97/43 EURATOM [3] are recommended to be introduced in each Member state, correspondingly adapted to the national law.

These criteria help in guaranteeing an adequate image quality, comparable throughout Europe and also keep the dose of exposure applied reasonably low. In this manner, the subjective impact is expected to be reduced: the radiologist in interpreting the image, the service engineer in repairing and adjusting the apparatus, the medical physicist in performing Q.A. and Q.C. procedures, even the manufacturer is supported in improving his production.

Contrary to this subjective assessment the risk may be quantitatively estimated by measurements and calculations of the amount of radiation the body has absorbed. Important units are: absorbed dose, equivalent dose (on the base of the relative biological effectiveness, including the weighting factors for the different kinds of radiation) and the effective dose, taking into account the different radiosensitivity of various tissues. The current values of these weighting factors are given in the Publication 60 of the ICRP[4].

The calculation algorithm follows the steps:

• measuring the needed data,
• calculating the absorbed dose by the concerned organ and correspondingly weighting it for the radiation applied,
• calculating the equivalent dose for each organ and weighting the dose by the risk factor,
• summing all calculated doses and calculating the effective dose for the whole body.

By means of the specialized measurement and control equipment (harmonizing devices and methods as well) the process of risk estimation may be viewed objectively - for the purposes of determining reference levels, of monitoring the medical exposure of the population, of statistics (comparison between diverse equipment and methods, relation to different tissues, and others). The reference levels should be treated as an aid for optimizing the radiation protection, the other two aspects being:

• diagnostic quality of the image achieved and
• the choice of the appropriate X-ray technics.

The general risk from the ionizing radiation in medicine should be considered as a part of a multifacette complex risk: for example an invasive session under x-ray control, or the case of incomplete or incorrect information and as sequence an inappropriate treatment, a new radiopharmaceutic, terminological problems and others... The absence or still insufficient level of information and understanding the nature and the benefit/loss ratio of the ionizing (and non-ionizing) radiation in the broadest strata of the population and the role of the mass-media are one of the most important challenges in the process of the risk management.

The direct risk as a result of a diagnostic investigation in fact is very low: if the procedure is justified and the equipment and protection - optimized the patient dose will be as low as it is possible from the medical point of view. A further dose reduction could in turn induce an additional risk (see above) to the patient.

In realizing a Project for harmonization with the EC-recommendations diverse activities are interdependently run in the following subject areas:

• changes in the national legislature and building-up an appropriate infrastructure,
• supply of the necessary equipment for measurement and control,
• creation of a national data base to estimate the risk to the population from medical exposure with reference levels,
• elaboration of programs for quality assurance and a system for quality control in diagnostic radiology and in radiotherapy,
• elaboration of a national program for training of the relevant staff (medical and paramedical),
• international seminars on radiation protection and modern approaches for image quality improvement,
• public awareness campaign (risk communication) incl. website on the Internet.

An intensive and fruitful collaboration with experts from the EU-Member states contributes to a quicker and more effective implementation of the results in the practice (a pilot study includes some big hospitals, where experienced staff is working and modern technology and methodology are practiced).

Non-Ionizing Radiation

"Risk" is the term moving the research of developing exposure limits for different hazards, especially for electromagnetic fields (EMF). We are not going here to advance the theory of the risk, and to discuss the ways and methods of risk assessment and management. We want only to mention the similarity of the risk of exposure to ionizing and non-ionizing radiation (NIR) - the synonym of a probability of harmful effect. There are discussed in some Eastern European Countries possibilities to use the same method to develop exposure limits for EMF exposure as that used for ionizing radiation. As a result, some precautionary approaches are used now in certain countries similar to these suitable for ionizing radiation. Concerning the whole range of NIR, the most complicated problem exists with EMF, not with optical radiation, nevertheless if it is irradiated by polychromatic lamps or by lasers. Here, we will take into account only those EMF.

Now, the safety factors used in the standards for EMF, include the uncertainty of both biological evidence and risk assessment, also the gaps of knowledge in the field of the EMF influence on human body. Safety factors of 1:10 and 1:50 to the adverse effect levels are used for establishing exposure limits for electromagnetic radiation. Where is the threshold limit value in this case?

The most important factor in the conception for developing exposure limits for EMF is the threshold conception, which is still in dispute for ionizing radiation. This means that in some standards both Threshold Limit Values (TLVs) and Maximal Permissible Levels (MPEs) are established.

With particular attention to EMF, Prof. Paltsev in [5,6] speaks about three different zones of biological reactions of the organism:

• biological effects;
• a progress of adaptive and cumulative processes as a manifestation of adverse effects on the systems;
• pathology.

The exposure limit for adverse effect should be the border dividing the zones of active adaptation and pathology.

The Subcommittee 4 of IEEE (Institute of Electronic and Electrotechnical Engineers) defines the adverse effect as follows: "An adverse effect is recognized by the appearance of a harmful change in health and well-being. For example, such changes include organic disease, impaired mental state, behavioral malfunction, reduced longevity, and defective of deficient reproduction."

Following the publication of Savin,BM [7], the following changes have to be taken into account when assessing the exposure:

1. Qualitative changes in the course of biological processes
2. Quantitative changes in the state of biological processes out of the physiological standard levels and resulting in the decrease of human compensation capacity to respond to environmental hazards or to overcome unusual psycho-physiological conditions.
3. Occurrence of additive effects of exposure with cumulative characteristics, leading at long term exposure to changes in the biological processes exceeding the permissible quantitative indices.

The following classification of the thresholds of electromagnetic radiation exposure by biological indicators is given in the same publication:

Compared with the ionizing radiation, the fundamental dosimetric quantity in radiological protection is the absorbed dose. This is the energy absorbed per unit mass and its unit is the J/kg. The same unit is used for the radiofrequency range of EMF - "specific absorption" (SA, J/kg), and the similar one "specific absorption rate" (SAR, W/kg), accepted for radiofrequency and microwave radiation exposure.

When the absorbed energy is considered, different methodology for studying the exposure limits of EMF exposure are used, depending on the wavelength:

• With a wavelength essentially exceeding the size of the biological object - frequency up to 30 MHz;
• With a wavelength much less than the size of the body;
• With a wavelength commensurable with the size of the body or with the sizes of different parts or organs - frequency between 30 MHz up to 10 GHz and above.

The exposure limits for adverse effect evaluated on the basis of extrapolation and by numerical methods of calculating the induction currents/absorbed energy in phantoms are better approximation than the direct transfer of data from animals to human body. The uncertainty of such extrapolations could reach to 50-100%, while for animal extrapolation it reaches 1-2 orders. [5,7]

Non-thermal effect exists when it is not observed whole body temperature rise. The heat distribution could be non-uniform, and "hot spots" could be available in field strengths below those causing thermal effect.

Now, the main problem is which definition should be developed for: "windows" and "resonance" effects, long-term and short-term effects, thermal and non-thermal effects, informational effects, adverse effects, biological effects, established effects, etc. The discussion on the terminology leads to different rationales and criteria for developing exposure limits. This is one of the main reasons that the general population doesn't believe in the proofs from science of exposure to EMF. As a result several countries accepted the "precautionary approach principle" in their legislation, and different societies try to include the "prudent avoidance" as an international principle to protect the people from EMF exposures.

A general national program for risk perception, risk communication and risk management has been developed and at present is in an implementation stage. This program can be used both for ionizing and non-ionizing radiation.

Bibliography:

1. Establishing a Dialogue on Risks from Electromagnetic Fields (Draft 2002), Radiation and Environmental Health, Department of Protection of the Human Environment, WHO, Geneva.
2. ICRP Publication 73: Radiological Protection and Safety in Medicine. Pergamon Press, Oxford, 1996
3. Council Directive 97/43 EURATOM on Health Protection of Individuals against the Dangers of Ionizing Radiation in Relation to Medical Exposure. Official Journal of the European Commission, L180, V22, 1997
4. ICRP Publication 60: 1990 Recommendations of the International Commission on Radiological Protection. Annals of the ICRP,21 Nos 1-3, Pergamon Press, Oxford,'91
5. Paltzev YP, GA Suvorov - Methodology of Hygienic Standardization of Electromagnetic Fields and their Hrmful Effects Evaluation on Man, Electromagnetic Fields, Biological Effects and Hygienic Standardization, WHO, Proceedings, Moscow, 1998. P.11-20.
6. Petlenko VP, ML Reznik - Philosophical Aspects of the Theory of Norms, and the Problem of the Standards Development, Methodological Questions of Hygienic Standardization of Non-Ionizing Radiation, Moscow, 1977, p.9-15.
7. Savin BM - Problem of Hygienic Standardization of Radiofrequency Electromagnetic Radiation, Methodological Questions of Hygienic Standardization of Non-Ionizing Radiation, Moscow, 1977, p.16-23.