The radiation protection com­munity should participate in the renewal of the ICRP recommen­da­­tions for radio­logical protection.

The recommendations of the ICRP [2] provide dose limits for planned exposure situations at the workplace and for the general population from artificial radiation sources. For existing exposure situations (for example, remains or legacies from previous activities with radioactivity or increased radon levels in residential buildings) and for radiological emergencies it suggests dose reference levels which are determined and enforced case by case by the relevant national authorities responsible for such emergency situations. The system of recommendations is periodically reviewed and, if necessary, adapted to new scientific findings and new requirements. In this regard the ICRP has recently announced that its recommendations for radiological protection will be revised in the coming years, to make them fit for purpose. ICRP has expressed its ­intention to do this in cooperation with the radiation protection community. We should accept this invitation and actively participate in this process.

Two major challenges in the system of radiation protection for which we need a solution.

In the view of practitioners, two issues deserve particular attention. On the one hand, we need an internationally coordinated and accepted set of rules for radon at the workplace and in the living area.
To do this, we need uniform conversion factors to convert the radon exposure from Bq · h/m³ into an effective dose in mSv per year [3].
Since the ICRP’s radiation protection concept is based on the effective dose as a measure for the comprehensive radiological health impact of ionizing radiation (i. e. the detriment as it is defined by the ICRP), it makes sense – when communicating with the media and the population – to also state the effective dose for radon in mSv per year and not just as a radon exposure in Bq · h/m³, as the latter is too difficult to understand for non-experts.
Radon is by far the largest single component of our radiation exposure. Its range of values extends over 2 to 3 orders of magnitude. It is important to raise awareness among authorities, the population and the media (as they are the most important communication channel between radiation protection experts and the public) about the issue of radon and the importance of countermeasures for buildings with high radon burden. For this purpose, the effective dose in mSv per year is the most suitable parameter, as it enables the comparison with the other dose components of our daily life.
Unfortunately, there is often a distorted perception here (even among experts and despite the clear definition of the effective dose by the ICRP): Fractions of a micro-Sievert per year due to radioactivity released by nuclear facilities are often subjectively judged to be more dangerous than the radiation exposure from radon in living areas, which in some cases can be up to or even more than 10 milli-Sieverts per year.

Dose to the lens of the eye

The second question concerns the ICRP regulation for the dose to the lens of the eye from 2011: Does this make sense from the user’s point of view? What are the cases where the dose to the lens of the eye is radiologically significant and justifies specific regulations and actions? Which activities pose the greatest risk, and which protective measures are most suitable and most efficacious?

Sustainability in radiation protection

By issuing the “Sustainability Development Goals”, the UN call 2015 for sustainability in all areas of our daily life. Sustainability has 3 pillars: Society, Environment, and Economy.

How should this requirement be implemented in practical radiological protection?

For the societal aspect, this means that applications of radiation and radio­activity – and not to forget also measures and actions to be taken in ­radiation protection – should be fair. So, an advantage in one population group should not become a disad­vantage in another one. Everyone should have the same chance to benefit from ­applications and protective measures.
The impact on the environment of applications and measures should be justified by a corresponding real benefit, i. e. an application should provide a real advantage. Measures taken in radiation protection should contribute to avoid a real amount (and not only a hypothetical one) of radiation dose, and so enable a real reduction of its associate radiological risks. The same applies to the expenditure on manpower, materials, energy, and costs for applications of radiation and radioactivity, as well as for measures to be taken in radiation protection. Measures that merely avoid only few hypothetical micro-Sievert but require a great deal of effort and lead to significant radiation doses for the employees involved in their implementation must be questioned regarding their sustainability. A further point is a respectful handling of raw materials, residues, and waste: As far as this is possible (i. e. where recycling makes sense and further is compatible with the principles of radiation protection), materials should always be recycled.

Continue to maintain LNT or look for alternative concepts?

For the dose range above 100 mSv, the large epidemiological studies such as LSS and INWOKRS, [4, 5] show a ­clearly recognizable linearity between radiation exposure and radio­logical ­effects, especially in terms of cancer mortality. Several comments on the INWORKS study (which includes over 300,000 employees from ­nuclear ­facilities in France, UK and USA for the years 1945 to 2005, covering 10.7 millions of person year) ­criticize the fact that the study does not consider natural radiation exposure (i. e. the ­cumulated radiation dose of between 20 to 100 mSv, according on the age of the employees and their ­duration of employment) and further, the doses caused by medical applications (for ­diagnostic or therapeutic purposes) of radiation they had received so fare.
However, below 100 mSv linearity is not clearly recognizable by both mentioned studies. The question is justified as to whether there is a lower dose threshold below which health effects are not to be expected or even hormetic effects [6, 7] may exist. If there is such a lower dose threshold, it would probably have to lie within the variation range of the natural radiation to which we are all constantly exposed and to which nature has adapted during evolution. Natural radiation may even be useful for the evolution of species, as Aristotle states “Nature does nothing uselessly”. If one ad the radiation doses from medical appli­cations and from other anthropogenic ­radiation sources, then – when omitting the high natural background ­radiation areas (HNBR) [8] – the total radiation exposures of the populations of most countries are within a dose range of between 1 and 20 mSv per year [16].
The LNT hypothesis – which goes back to the American geneticist Hermann Joseph Muller (1890–1967; Nobel Prize in physiology and medicine in 1946) and was adopted by ICRP in 1959 – cannot be proven by epidemiological studies for the dose range below 100 mSv per year and remains therefore a hypothesis.
Since some years LNT is increasingly being questioned, and this also by serious scientists. Some of the points raised in their criticism are weighty and diverse [9].
Now that the ICRP’s recommendations on radiological protection are due to be renewed, we should face this debate and examine whether we should maintain LNT or should limit its application to the range above 100 mSv per year or should look for alternatives and check their justification and usefulness for practical radiation protection.
Ignoring this criticism and not engaging in this discussion would undermine the ICRP’s credibility [10]. Of the many works that are critical of LNT [11], the one commissioned by the French Academy of Sciences and the Academy of Medicine should be mentioned [12]. It is probably one of the most comprehensive and competent works on this topic.
In fact, all these questions have already been discussed several times by radiation protection experts. But until now, even those who have expressed themselves critically about the LNT have lacked the courage to consider any further actions, because a whole series of fundamental questions would then arise and need to be answered.
Another issue that would need to be discussed is the inclusion of radiation induced epigenetic effects [13] in the models used to calculate biological effects of ionizing radiation. Epi­g­enetics describes the changes in genetic expression – which can be hereditable to a certain extent – but which are not changes in the DNA sequence itself. So, epigenetics makes the link between genotype and phenotype.

What would be the consequences abandoning LNT or restricting it to the dose range above 100 mSv per year?

We would then have to reflect on some of the basic principles in radiation protection, such as ALARA or the dose limit values. The setting of dose limit values for planned exposure situations – that means 20 mSv per year at the workplace and 1 mSv per year for the rest of the population from anthropogenic radiation sources – are until now based on a maximum tolerable value for the radiation risk in terms of detriment as defined by the ICRP. The dose corresponding to this radiological risk is then calculated using the ICRP radiation risk coefficients and the LNT hypothesis for the extrapolation to low doses. But the mentioned dose limits – i. e. 1 and 20 mSv per year – are at the lower end of the dose range from 0 to 100 mSv, where linearity is no longer evident. This leads inevitably to the search for other justifications for the dose limit values in radiation protection.

Do we need a lower end for ­optimization measures in radiation protection?

For planned exposure situations the dose limits of 20 mSv per year for the workplace and 1 mSv per year for the rest of the population from anthropogenic radiation sources are well established and are not seriously questioned.
A further reduction of these limit values is not considered necessary by the radiation protection community.
For years, however, we have been discussing on the interpretation of “ALARA”, as well as on the meaning of “Justification, Optimization or Reasonableness”.
Optimization is a basic principle not only in radiological protection. Optimizing a process means finding the greatest benefits with the fewest disadvantages. However, it would be wrong to understand optimization only as the requirement to minimize radiation exposures.
The following questions should be discussed with practitioners:
How should the recommendation of optimization in radiation protection be understood?
How far down should this optimization go?
Is there an acceptance threshold for the dose below which measures to further reducing radiation exposure are neither sensible nor justified?
This means that no further regulations would be necessary in this dose domain in the sense of the Roman legal principle:
“De minimis non curat lex”.
This approach gives those involved in radiation protection more personal responsibility (so that they are more than just enforcers of legal measures) by allowing them to use their own professional experience and expertise. However, even where the law does not provide any regulations, the ­usual precautionary measures when handling dangerous substances and ­devices must be observed and it ­remains important to act responsibly.
Applied in practice, this could mean (as has been suggested by Michel et al on behalf of the German-Swiss Fachverband für Strahlenschutz [1]) that no further measures are necessary below 1 mSv per year at the workplace, or below 0.1 mSv per year for the general population from anthropogenic radiation sources.
In the opinion of the authors [1], measures below the stated values are no longer justified, as their contribution to the reduction of the total radiation exposure (and the corresponding radiological risk) is insignificant and has no measurable impact on public or individual health, compared to the already existing doses and risks and their large variation domain [17].
Of course, the usual basic rules should not be disregarded, i. e. avoid staying in the radiation field unnecessarily, only people in the radiation protection area who must be there, contamination controls where there is a risk of contamination or incorporation of radioactivity.

Do we need a holistic assessment of radiation doses and radiation risks?

Security and safety are always relative. How safe an activity or facility is, can only be assessed by comparing it with appropriate alternatives. Unfortunately, the perception of safety or risks is rather subjective, as is the balance between the appreciation of the benefits (or the chances) that an activity or facility provides and the willingness to accept the associated risks. Providing factual and objective information about safety and risks is therefore a major challenge for the radiation protection experts.
When optimizing activities and facilities with the aim to minimize risks, one should be focused on the objectively largest ones, as this is the best way to significantly reduce the overall risk. This shows the need for a holistic assessment of both the risks and – in radiation protection – the exposure to radiation and its associated risks. Specifically, this means that an individual’s radiation exposure from anthropogenic radiation sources can only be assessed objectively in comparison to her or his radiation exposure from natural and all other sources combined.
Natural radiation exposure – above all that caused by radon in living areas – is by far the largest component of the overall radiation exposure and has a very wide range of variation. It depends on many parameters, such as geology, altitude, radon in the living area, building materials, diet, and other influencing factors. In exceptional cases, such as residential buildings with very high levels of radon or in high natural background radiation areas, the radiation doses can go up to 200 mSv per year, in some cases even more than that. Apart from the high natural background radiation areas, the natural radiation exposure in most countries lies between about 1 and 20 mSv per year. In addition, there are doses from medical applications and, in some cases, from professional ­activities. Here, civil aviation personnel are among the people most exposed to radiation, and not, as one might assume, the employees of nuclear facilities.
If a person receives an additional dose of 0.1 mSv per year through an activity or a facility, this means an increase in the total radiation exposure of 10 %, in the case this person receives annually 1 mSv from natural radiation sources. It means an increase of only 0.5 % in the case she or he receives 20 mSv per year from natural radiation sources.
A holistic assessment is also recommended when it comes to the assessment of risks, especially those of cancer mortality. Carcinogenesis is a complex process in which age, genetics (and epigenetics), gender, lifestyle (for example cigarette smoking), diet (nutritional habits), air pollution, geographical region of residence, occupational exposure, and many other factors – probably including individual mental health – play an important role. Cancer incidence and cancer mortality show a large range of variation. In 29 European countries the average cancer mortality rate per country varies between 200 and 350 per year per 100’000 inhabitants. Furthermore, cancer mortality increases sharply with age and is approximately one and a half times higher in men than in women. Of the overall cancer mortality, only a small part is probably attributable to natural radiation exposure, while the contributions of other influencing factors remain certainly more important.

Should radiation protection go towards individual dosimetry and risk assessment?

The radiation risk of an individual depends not only on the dose she or he receives. The radiation risk depends also on gender, age, genetics (eventually also on epigenetics), lifestyle, geographical region of residence, as well as previous exposures to other causes that can induce a cancer (because of the multiplicative radiation risk projection).
The Detriment adjusted nominal risk coefficients of ICRP for cancer and heritable effects (usually given in 10–2 per Sievert effective dose) are population averaged and age standardized values (and only for a standard adult person) and do not consider the individual radiation sensitivity nor a multiplicative connection between radiation risk and the spontaneous or baseline (mainly cancer) risk of an individual.
The use of these risk coefficients is problematic for 2 reasons:
They should not be used to calculate an individual person’s risk of death from cancer (or a heritable disease among his or her descendants), nor – the ICRP explicitly warns against this – should they be used in the low dose range (where linearity between dose and detriment is not evident) to calculate hypothetical cancer deaths in collectives [19].
Where else should these risk coefficients be used at the end?
This justifies the question of whether we need an individual dosimetry and an individual assessment of the ­radiation risks to take the above-­mentioned issues into account appropriately.
The ICRP risk coefficients should therefore not be used for ­calculations for which they are not intended (i. e. by the ICRP).
An improper use of these risk coefficients may cause unfounded concern about radiation [20] and fear of radiation may make more ­people sick than radiation itself.
And this precisely is not the aim of radiation protection and is further ­incompatible with its ethical principles.