# Essentials of the system of radiological protection

Werner Rühm, Kimberly Applegate, Nobuhiko Ban, Francois Bochud, Simon Bouffler, Kun-Woo Cho, Chris Clement, Eduardo Gallego, Olga German, Gillian Hirth, et al.

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Werner Rühm, Kimberly Applegate, Nobuhiko Ban, Francois Bochud, Simon Bouffler, et al. Essentials of the system of radiological protection. Journal of Radiological Protection, 2025, 45, pp.033002. 10.1088/1361-6498/ae02a2. hal-05444319

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**MEMORANDUM • OPEN ACCESS**

# Essentials of the system of radiological protection

To cite this article: Werner Rühm et al 2025 J. Radiol. Prot. 45 033002

View the [article online](#) for updates and enhancements.

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MEMORANDUM

Essentials of the system of radiological protection

Werner Rühm<fnref n="1" />,*, Kimberly Applegate<fnref n="2" />,<fnref n="21" />, Nobuhiko Ban<fnref n="3" />, Francois Bochud<fnref n="1" />, Simon Bouffler<fnref n="5" />, Kun-Woo Cho<fnref n="6" />, Chris Clement<fnref n="7" />, Eduardo Gallego<fnref n="8" />, Olga German<fnref n="7" />, Gillian Hirth<fnref n="9" />, Makoto Hosono<fnref n="10" />, Michiaki Kai<fnref n="11" />,<fnref n="12" />, Dominique Laurier<fnref n="13" />, Senlin Liu<fnref n="14" />, Nicole E Martinez<fnref n="15" />, Sergey Romanov<fnref n="16" />, Thierry Schneider<fnref n="17" />, David G Sutton<fnref n="18" /> and Andrzej Wojcik<fnref n="19" />,<fnref n="20" />

E-mail: wruehm@bfs.de

**Keywords:** system of radiological protection, ICRP, LNT

Abstract

The system of radiological protection (the ‘System’) developed by the International Commission
on Radiological Protection (ICRP) is built on nearly a century of efforts of numerous scientists and
practitioners working together internationally. It rests on three enduring pillars: science, ethics,
and experience. These pillars support the three fundamental principles that shape radiological
protection strategies: justification, optimisation, and application of dose limits. Of note,
optimisation of protection must be understood as a flexible and context-sensitive process, which
allows identification of the appropriate level of protection, not simply the lowest dose, taking into
account economic, societal and environmental factors. The System has proven effective in
protecting workers, patients, members of the public, and the environment in all exposure
situations. Effects of high doses, where acute injuries to healthy tissue occur, are rarely observed,
and mostly due to accidental situations except for unavoidable side effects of radiotherapy. At low
doses, the System is supported by application of the linear-no-threshold model. This model enables
prudent (that is, carefully considered given existing uncertainties) policy decisions and estimation
of risks at low doses by extrapolation from epidemiological data observed at medium and high
radiation doses, acknowledging uncertainty without ignoring potential harm.

<footnote n="1">¹ Federal Office for Radiation Protection, Ingolstädter Landstraße 1, D-85764 Neuherberg, Germany</footnote>

<footnote n="2">² University of Kentucky College Medicine, 800 Rose Street MN 150, Lexington, KY, 40506, United States of America</footnote>

<footnote n="3">³ Nuclear Regulation Authority, 1-9-9 Roppongi, Minato-ku, Tokyo 106-8450, Japan</footnote>

<footnote n="4">⁴ Institute of Radiation Physics, Lausanne University Hospital and University of Lausanne, Rue du Grand-Pré 1, CH-1007 Lausanne, Switzerland</footnote>

<footnote n="5">⁵ UK Health Security Agency, Radiation Protection Sciences Division, Didcot, Oxon OX11 0RQ, United Kingdom</footnote>

<footnote n="6">⁶ Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141 Republic of Korea</footnote>

<footnote n="7">⁷ International Commission on Radiological Protection, 350 Albert Street, Ottawa, Ontario K1R 1A4, Canada</footnote>

<footnote n="8">⁸ Energy Engineering Department, School of Industrial Engineering, Universidad Politécnica de Madrid, José Gutiérrez Abascal 2, 28006 Madrid, Spain</footnote>

<footnote n="9">⁹ Australian Radiation Protection and Nuclear Safety Agency, 619 Lower Plenty Road, Yallambie, VIC 3085, Australia</footnote>

<footnote n="10">¹⁰ Kindai University Faculty of Medicine, 377-2 Ohno-Higashi, Osaka-Sayama, 589-8511 Osaka, Japan</footnote>

<footnote n="11">¹¹ Nippon Bunri University, 1727 Ichigi, Oita 870-0397, Japan</footnote>

<footnote n="12">¹² Radiation Effects Association, 1-9-16 Kajicho, Chiyoda-ku, Tokyo 101-0044, Japan</footnote>

<footnote n="13">¹³ French Nuclear Safety and Radiation Protection Authority (ASNR), 31 Avenue de la Division Leclerc, 92262 Fontenay aux Roses, France</footnote>

<footnote n="14">¹⁴ China Institute of Atomic Energy, PO Box 275 (1), Beijing CN-102413, People's Republic of China</footnote>

<footnote n="15">¹⁵ School of Civil & Environmental Engineering and Earth Sciences, Clemson University, Clemson, SC, United States of America</footnote>

<footnote n="16">¹⁶ Southern Urals Biophysics Institute, Ozyorsk, Chelyabinsk Region, Russia</footnote>

<footnote n="17">¹⁷ Nuclear Protection Evaluation Centre, 28, rue de la Redoute, F-92260 Fontenay aux Roses, France</footnote>

<footnote n="18">¹⁸ School of Science & Engineering, University of Dundee, Dundee DD1 4HN, United Kingdom</footnote>

<footnote n="19">¹⁹ Centre for Radiation Protection Research, Stockholm University, Svante Arrheniusväg 20C, 106 91 Stockholm, Sweden</footnote>

<footnote n="20">²⁰ Institute of Biology, Jan Kochanoski University, 25-406 Kielce, Poland</footnote>

<footnote n="21">²¹ Retired.</footnote>

<footnote>* Author to whom any correspondence should be addressed.</footnote>
# 1. Introduction

The System developed by the International Commission on Radiological Protection (ICRP) forms the basis of protection regulations all over the world (ICRP 2007a). In fact, every day modern radiation protection benefits millions of patients undergoing diagnosis and treatment, millions of workers exposed to ionising radiation in the workplace, and billions of people exposed to natural sources of ionising radiation. To make sure that the System is applied as intended—which is of particular importance in times of heated scientific and political debates—this memorandum serves as a reminder of the foundation on which the System rests.

# 2. Radiological protection and the ICRP

Since the discovery of x-rays in 1895 numerous scientists from all over the world have studied the health and environmental effects of exposure to ionising radiation with the goal of developing and improving radiological protection guidelines, to protect people and the environment against the detrimental effects of ionising radiation (Kathren and Ziemer 1980, Lindell 1996, Boice et al 2020). As a result, workers, patients, members of the public, and the environment are safeguarded when ionising radiation is used properly in research, medicine and industry. In emergencies, protective actions have been developed to mitigate, as far as possible, radiological consequences for people and the environment.

For almost 100 years, ICRP has coordinated these efforts and issued radiological protection recommendations that have been broadly recognised and adopted into national legislation (Clark and Valentin 2009). ICRP is a politically and financially independent, non-governmental organisation formally registered as a charity with the Charity Commission of England and Wales. ICRP's mission is to advance radiological protection for the public benefit, with the aim of protecting patients, workers, the public, and the environment against detrimental effects of ionising radiation exposure, without unduly limiting the benefits associated with the uses of ionising radiation.

# 3. The three enduring pillars of the system

The System rests on three enduring pillars—science, ethics, and experience (ICRP 2007a). In other words, the System is evidence-based, informed by and evolved through consideration of multiple lines of reasoning.

Numerous renowned experts in radiation research regularly review the international scientific literature and discuss their results with other leading international organisations with interests in radiological protection. Consequently, the recommendations of ICRP are consistent with current scientific evidence on the effects of radiation exposure in humans and non-human biota.

Due to broad international consultation with ethicists and social scientists, the System is based on common ethical values and principles that are shared all over the world, such as doing good, avoiding harm, prudence, justice, and dignity (ICRP 2018). These are the pre-requisites for the ICRP recommendations to be considered useful and widely incorporated into national law across cultures.

Finally, the ICRP recommendations have been developed building on the experience of generations of practitioners. In consequence, the ICRP recommendations include practical guidance such that they are broadly applicable in a wide variety of contexts and situations.

# 4. The three fundamental principles of the system

The System is governed by three fundamental principles—justification, optimisation of protection, and application of dose limits (ICRP 2007a).

The principle of justification involves the process of determining whether an exposure to ionising radiation is beneficial overall, i.e., whether the benefits to individuals or to society of any proposed action involving ionising radiation outweigh the harm or damage it might cause given the circumstances. This principle ensures that unjustified radiation exposures are avoided, i.e., that there is an overall net benefit of any activity involving ionising radiation. Justification is also applied to protective actions in case of an emergency, as well as to remediation (clean-up) decisions, resulting in decisions that weigh all positive and negative consequences (including non-radiological) and possible levels of exposure caused by the actions in question.

The principle of optimisation of protection involves managing exposures by considering the likelihood of exposures occurring, the number of individuals exposed, and the need to keep individual doses as low as reasonably achievable, taking into account economic, societal, and environmental factors (ICRP 2020).
Optimisation of protection is about balancing the benefits and detriments of protective actions to achieve the greatest overall benefit. This does not always mean reducing doses; rather, it involves finding the best overall outcome. For example, it supports further reductions in occupational exposures even when they are already below dose limits (ICRP 2006). It also allows for increased doses when justified, such as in medical imaging or radiotherapy, to achieve the best possible outcome (ICRP 2023).

Finally, the principle of application of dose limits involves the use of controls (ICRP 2007b) over the exposure of an individual to ensure that the risk of radiation health effects such as cancer is tolerable and tissue effects such as skin burns and acute radiation sickness are prevented. Of note, dose limits do not apply to medical exposures, to avoid interference with medical imaging involving ionising radiation and with radiotherapy. The application of this principle helps ensure in the context of ethical considerations, that in a group of people exposed to ionising radiation there is a fair distribution of doses avoiding some individuals being significantly more exposed than others (ICRP 1991, 2018).

## 5. The linear-no-threshold (LNT) model

The System is based on the application of the LNT model for protection against radiation-related stochastic effects such as cancer. The LNT model implies that the risk of getting cancer can be described as a simple linear function of dose, with no threshold below which effects are absent. Of note, in recent years there has been growing evidence from the majority of epidemiological studies that radiation cancer risk in humans indeed exists in the low dose range, with a shape of dose-response which is coherent with a linear model (NCRP 2018, Hauptmann et al 2020, Rühm et al 2022, Laurier et al 2023, Wakeford et al 2023). The hypothesis of an absence of a threshold is not specific to ionising radiation, but also applies to many carcinogens, such as smoking, alcohol or chemicals. The LNT model makes it possible to estimate the cancer risk at low doses from existing epidemiological evidence (Laurier et al 2023, Wakeford et al 2023). Combined with LNT, a risk reduction factor of 2 is applied in the low dose range reflecting a lower effectiveness of ionising radiation to induce cancer at low dose or low dose rate (ICRP 2007a).

In fact, it is known that at low doses, some cellular responses that are potentially relevant for human cancer induction are non-linear with dose. Some of those responses might point towards lower health risks at low doses than a linear extrapolation down to low doses would imply. Others, however, might point towards higher health risks. These cellular reactions do not provide quantitative indicators of cancer risk as epidemiological studies do. However, they are not in contradiction to the use of the LNT model for radiological protection purposes (UNSCEAR 2021).

The underlying basis of the System must be robust to permit handling of complex situations and consideration of complex scientific, ethical, and practical issues. Taken the overall current scientific epidemiological and biological evidence, ICRP considers the application of the LNT model for the purpose of radiological protection as science-based, practical and prudent (ICRP 2007a). In this context prudence does not mean to choose the lowest risk alternative. Rather, being prudent means here the making of an informed and carefully considered choice on human cancer risk without sufficient epidemiological evidence and the full knowledge of the underlying biological mechanisms. The directly proportional relationship between risk and dose makes the LNT model a very practical tool for radiological protection, particularly for facilitating optimisation.

## 6. Conclusions

Through the application of the System, acute tissue injury is only rarely encountered, mostly due to accidental situations except for unavoidable side effects of radiotherapy. Much of radiological protection today is concerned with low dose exposures where cancer risks may be increased. The use of the LNT model has served radiological protection and public health well. Application of the justification and optimisation principles has encouraged the reduction of exposures to a reasonable extent whereby a good level of protection can be achieved.

The pillars and principles of the System are long-established and fundamental. They guarantee that the System remains up-to-date and fit for purpose. To make sure that this will also hold in the future, ICRP has recently requested in the Vancouver call for action that expertise in radiological protection is strengthened worldwide. This can be achieved for example through national governments and funding agencies providing sufficient resources for radiological protection research, through national research laboratories and other institutions launching and sustaining long-term research programmes, and through universities developing undergraduate and graduate educational programmes (Rühm et al 2023).
The ICRP recommendations are science-based, rest on ethical values, and are practical. Their aim is to ensure an adequate level of protection of people and the environment while supporting sustainable development in the medical, veterinary, industrial, agricultural and environmental sectors, space exploration and other areas of modern society where radiation and radioactive sources comprise an integral part of the progress. Based on almost one hundred years of experience, ICRP will continue to serve as the steward of the system of radiological protection and develop it further as needed, for the benefit of all.

## Data availability statement

No new data were created or analysed in this study.

## Acknowledgment

The authors represent the current and former ICRP Main Commission and the ICRP Scientific Secretariat. They report no conflict of interest.

## ORCID iDs

Werner Rühm ID 0000-0002-6354-7359

Kimberly Applegate ID 0000-0001-7716-1636

Nobuhiko Ban ID 0000-0001-7583-3806

Francois Bochud ID 0000-0003-2076-0296

Simon Bouffler ID 0000-0003-1883-919X

Kun-Woo Cho ID 0000-0002-7723-6973

Chris Clement ID 0000-0003-1343-2585

Eduardo Gallego ID 0000-0001-8338-4959

Olga German ID 0009-0001-3255-1742

Gillian Hirth ID 0000-0002-5478-1127

Makoto Hosono ID 0000-0001-8040-3245

Michiaki Kai ID 0000-0001-7812-727X

Dominique Laurier ID 0000-0003-1432-4738

Nicole E Martinez ID 0000-0002-7184-3043

Sergey Romanov ID 0000-0002-8642-3850

Thierry Schneider ID 0000-0003-0094-5293

David G Sutton ID 0000-0003-2786-4506

Andrzej Wojcik ID 0000-0002-3951-774X

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