Summary of a note on system of radiological protection

A paper, termed as memorandum, on the essentials of system of radiological protection (SRP) has been published in the Journal of Radiological Protection (Vol. 45, 2025, 033002) by radiation protection professionals, who are members (past/present) on various committees of the International Commission on Radiological Protection (ICRP). The note summarizes and lists various issues currently being pursued or discussed by many professionals of radiation protection. A clear detail is presented on the application of linear no-threshold (LNT) and the three fundamental principles of radiation protection. The SRP is based on three pillars of science, ethics, and experience. The three fundamental principles of justification, optimization, and dose limits have enabled in developing the radiation protection policies and regulations all over the world and also for many decades. The paper helps in understanding the reasons or circumstances behind the use of SRP and LNT for radiological protection of radiation workers, patients, the public, and the environment. The three aspects of radiological protection which are in use for many decades are as described below. PILLARS OF SYSTEM OF RADIOLOGICAL PROTECTION The SRP rests on three pillars of science, ethics, and experience. Researchers and professionals involved in setting the standards undertake extensive research and review of data generated in scientific studies on radiation over a long period including the latest and use it for developing policy. This activity is a continuous process and always updated as new research evolves. Ethics part takes into account of avoiding harm, doing good to society, and providing justice, which are incorporated in ICRP recommendations. The important pillar is of experience which is extensively used in formulating radiation protection standards. The experience of professionals working in various branches such as nuclear facilities, medical diagnostics, cancer treatment, high background radiation areas, and fallout studies from nuclear accidents is utilized. FUNDAMENTAL PRINCIPLES OF SYSTEM OF RADIOLOGICAL PROTECTION The three fundamental principles of SRP are justification, optimization, and dose limits. Justification primarily aims at achieving an objective of doing more good than causing a harm to an individual or society in establishing a nuclear facility, which has the potential of releasing radionuclide material and causing radiation exposure. A facility is not approved or justified unless the benefits from it to the society over weigh the detriment or disadvantage or harm. Optimization principle is taken care of by establishing a cost–benefit relationship and also by practicing as low as reasonably achievable. The risk of stochastic effects due to radiation exposure should either be lower or on par with the risks expected from other industrial establishments. To achieve such balancing objective, individual doses may also be further reduced even when the doses are already much below the dose limits. It also enables an increase in the dose limits when justified in cases such as medical diagnostics or radiation therapy. The dose limits recommended by ICRP are widely followed by national regulators and governments to control the exposures to individuals, workers, patients, and also the environment. The dose limits are established to minimize the stochastic effects and prevent/avoid deterministic effects. Different states/regulators devise their own dose limits for operational convenience on the lower side of ICRP dose limits to achieve the best goals without any additional costs on the operator or burden on radiation workers. The system, in other words, has been in excellent use for many decades, facilitating its application also in future for many more decades with time-to-time inclusion of new findings from the ongoing research on radiation effects. LINEAR NO-THRESHOLD MODEL This model is applied for protection of workers against stochastic effects due to radiation exposure. The model has no threshold dose below which the effects are absent, and it implies that the risk of stochastic effects is a linear function with dose. A risk reduction factor of 2 is applied to reflect the lower effectiveness of ionizing radiation to induce cancer at low dose range. The proportional relationship between risk of cancer and the dose makes the LNT model a practical tool for radiological protection. Although there are divergent views on the application of LNT model, authors give detailed reasons as to what the observed effects are at lower doses and also from epidemiological studies. The recent studies on epidemiological studies show some evidence that cancer risk in humans exists in the low dose range. It also has indicated that at lower doses, some cellular responses relevant to human cancer induction are nonlinear with dose, which point to lower health risks at lower doses. However, the cellular responses do not provide quantitative indicators of cancer risk as compared to epidemiological studies. ICRP considers the application of LNT model as a science-based, practical, informed, and carefully considered model on human cancer risk without sufficient epidemiological evidence and also full knowledge of underlying biological mechanisms. COMMENTS In view of the consideration of ICRP, to bring out replacement for 2007 general recommendations, this memorandum and many publications (where epidemiological, biological, and other radiation research studies are published) since 2007 and till today play an important role in framing the future direction for radiological protection for many more decades (https://www.icrp.org/page.asp?id=673). The undertone of research publications from the members of ICRP committees and others indicates that the three fundamental principles of SRP might remain as the pillars with more evidence coming in for their continuation. It is highly expected that the LNT model may also be retained for framing policies, setting dose limits, and risk estimation following radiation exposure at nuclear facilities, in emergency situations, in medical exposure, and also for high background radiation areas. Increased research on radiation effects and epidemiological studies is particularly needed in the coming decades to help improve the assumptions, if any, by providing quantitative experimental/science-based evidence for human cancer risk at low-dose range exposures (a call for this has already been made during 2022/2023 in ICRP Vancouver call 2023 for strengthening expertise in radiation protection and to address global shortage of expertise). I take this opportunity to express my gratitude to the authors for this excellent publication and declare that I have no personal interest in this editorial except that the message contained in the memorandum publication be spread among the radiation professional in India and other Asian countries.

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