Influence of neutron cross-section resonances on organ/tissue equivalent and effective dose coefficients for the ICRP voxel phantoms.

The materials which compose the ICRP Voxel phantoms used in the computation of conversion coefficients involve neutron interaction cross-sections that have resonances at specific energies. Depending on the energy bin structure used in the computations, these cross-section resonances may occur at energies that fall between energies at which dose coefficients are computed, thus their effects may not be completely accounted for in the reported coefficients. In the present study, a highly refined energy grid that closely follows the resonance structure in the phantom material cross-sections was identified and used to calculate dose coefficients. Both the equivalent organ/tissue doses for male and female voxel phantoms were computed as well as their summation to obtain the effective dose coefficients. The used refined energy grid tracks very closely the cross-sections in the vicinity of the resonances. The resulting refined energy grid coefficients are compared to coefficients for the coarser energy grid used in ICRP Publication 116. Additionally, reference spectra have been folded with both the fine and coarse sets of conversion coefficients. The resulting total effective doses for these reference spectra are used to assess the adequacy of the dose coefficients calculated on the original ICRP 116 energy grid. The dose coefficients were similarly computed for the local skin dose on the trunk of the body using the ICRU Report 95 phantom. The overall impact of the resonances on the organ/tissue equivalent dose, the effective dose, and the local skin dose are presented and discussed. In general, it was found that resonances can impact neutron dose coefficients, but in most cases the wide range of neutron energies encountered minimized this effect. The impact of resonances was further limited when computing effective dose due to organ/tissue summing and sex-averaging. For the neutron fields studied here, the impact was below 5%.

The scientific nature of the linear no-threshold (LNT) model used in the system of radiological protection.

During the first half of the 20th century, it was commonly assumed that radiation-induced health effects occur only when the dose exceeds a certain threshold. This idea was discarded for stochastic effects when more knowledge was gained about the mechanisms of radiation-induced cancer. Currently, a key tenet of the international system of radiological protection is the linear no-threshold (LNT) model where the risk of radiation-induced cancer is believed to be directly proportional to the dose received, even at dose levels where the effects cannot be proven directly. The validity of the LNT approach has been questioned on the basis of a claim that only conclusions that can be verified experimentally or epidemiologically are scientific and LNT should, thus, be discarded because the system of radiological protection must be based on solid science. The aim of this publication is to demonstrate that the LNT concept can be tested in principle and fulfils the criteria of a scientific hypothesis. The fact that the system of radiological protection is also based on ethics does not render it unscientific either. One of the fundamental ethical concepts underlying the LNT model is the precautionary principle. We explain why it is the best approach, based on science and ethics (as well as practical experience), in situations of prevailing uncertainty.

Synergistic Enhancement of Chemotherapy-Induced Cell Death and Antitumor Efficacy against Tumoral T-Cell Lymphoblasts by IMMUNEPOTENT CRP.

T-cell malignancies, including T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL), present significant challenges to treatment due to their aggressive nature and chemoresistance. Chemotherapies remain a mainstay for their management, but the aggressiveness of these cancers and their associated toxicities pose limitations. Immunepotent CRP (ICRP), a bovine dialyzable leukocyte extract, has shown promise in inducing cytotoxicity against various cancer types, including hematological cancers. In this study, we investigated the combined effect of ICRP with a panel of chemotherapies on cell line models of T-ALL and T-LBL (CEM and L5178Y-R cells, respectively) and its impact on immune system cells (peripheral blood mononuclear cells, splenic and bone marrow cells). Our findings demonstrate that combining ICRP with chemotherapies enhances cytotoxicity against tumoral T-cell lymphoblasts. ICRP + Cyclophosphamide (CTX) cytotoxicity is induced through a caspase-, reactive oxygen species (ROS)-, and calcium-dependent mechanism involving the loss of mitochondrial membrane potential, an increase in ROS production, and caspase activation. Low doses of ICRP in combination with CTX spare non-tumoral immune cells, overcome the bone marrow-induced resistance to CTX cell death, and improves the CTX antitumor effect in vivo in syngeneic Balb/c mice challenged with L5178Y-R. This led to a reduction in tumor volume and a decrease in Ki-67 proliferation marker expression and the granulocyte/lymphocyte ratio. These results set the basis for further research into the clinical application of ICRP in combination with chemotherapeutic regimens for improving outcomes in T-cell malignancies.

Review of ethical values across the ICRP's system of radiological protection.

In 2018, the International Commission on Radiological Protection (ICRP) released Publication 138, which highlights the ethical values foundational to the system of radiological protection. Additional work, both within and beyond the ICRP, has proposed or recommended ethical values associated with applications of the system in different areas, perhaps most notably in medical, veterinary, and environmental radiological protection. There are also existing ethical frameworks not specifically related to radiological protection that are nonetheless relevant to its practice; for example, the Beauchamp and Childress principles of biomedical ethics are of particular significance when it comes to medical uses of radiation and radioactivity. At first glance, it may seem as if there are unique or isolated sets of ethical values that need to be applied depending on the circumstance. Yet while each area of application will indeed have its own unique aspects and associated value judgements, there are consistent and complementary relationships between these ethical values. This paper reviews the work of the ICRP related to ethics, including brief historical context, and highlights the similarities and differences between sets of ethical values with emphasis on medical, veterinary, and environmental applications of radiological protection.

Absorbed dose coefficients for pediatric differentiated thyroid cancer patients undergoing radioiodine therapy.

The escalating incidence of differentiated thyroid cancer (DTC) in pediatric patients and the resultant growing use of radioactive iodine (RAI) reinforce the need to evaluate radiation exposure to normal tissues and radiation-induced health risks in pediatric patients undergoing RAI therapy. In the current study, we calculated absorbed dose coefficients (i.e. absorbed dose per unit activity administered, mGy MBq-1) specific for pediatric patients with localized DTC undergoing RAI therapy following total thyroidectomy for use in epidemiological studies. We first modified previously-published biokinetic models for adult thyroid cancer patients to achieve a reasonable agreement with iodine biokinetics observed in pediatric patients or design principles addressed in the International Commission on Radiological Protection (ICRP) reference age-specific biokinetic models. We then combined the biokinetic models in conjunction withSvalues derived from ICRP reference pediatric voxel phantoms. The absorbed dose coefficients for pediatric patients were overall greater than those for adults with a ratio (pediatric/adult) up to 11.6 and rapidly decreased with increasing age. The sensitivity analysis showed that the renal clearance rate andSvalues may have the greatest impact on the absorbed dose coefficients with the rank correlation coefficients ranging from -0.53 to -0.82 (negative correlations) and from 0.51 to 0.80 (positive correlations), respectively. The results of the current study may be utilized in clinical or epidemiological studies to estimate organ-specific radiation absorbed doses and radiation-associated health risks among pediatric thyroid cancer patients.

Mathematical complexities in radionuclide metabolic modelling: a review of ordinary differential equation kinetics solvers in biokinetic modelling.

Biokinetic models have been employed in internal dosimetry (ID) to model the human body's time-dependent retention and excretion of radionuclides. Consequently, biokinetic models have become instrumental in modelling the body burden from biological processes from internalized radionuclides for prospective and retrospective dose assessment. Solutions to biokinetic equations have been modelled as a system of coupled ordinary differential equations (ODEs) representing the time-dependent distribution of materials deposited within the body. In parallel, several mathematical algorithms were developed for solving general kinetic problems, upon which biokinetic solution tools were constructed. This paper provides a comprehensive review of mathematical solving methods adopted by some known internal dose computer codes for modelling the distribution and dosimetry for internal emitters, highlighting the mathematical frameworks, capabilities, and limitations. Further discussion details the mathematical underpinnings of biokinetic solutions in a unique approach paralleling advancements in ID. The capabilities of available mathematical solvers in computational systems were also emphasized. A survey of ODE forms, methods, and solvers was conducted to highlight capabilities for advancing the utilization of modern toolkits in ID. This review is the first of its kind in framing the development of biokinetic solving methods as the juxtaposition of mathematical solving schemes and computational capabilities, highlighting the evolution in biokinetic solving for radiation dose assessment.

ICRP workshop on the review and revision of the system of radiological protection: a focus on research priorities-feedback from the international community.

In September 2022, the International Commission on Radiological Protection (ICRP) organised a workshop in Estoril, Portugal, on the 'Review and Revision of the System of Radiological Protection: A Focus on Research Priorities'. The workshop, which was a side event of the European Radiation Protection Week, offered an opportunity to comment on a recent paper published by ICRP on areas of research to support the System of Radiological Protection. Altogether, about 150 individuals participated in the workshop. After the workshop, 16 of the 30 organisations in formal relations with ICRP provided written feedback. All participants and organisations followed ICRP's view that further research in various areas will offer additional support in improving the System in the short, medium, and long term. In general, it was emphasised that any research should be outcome-focused in that it should improve protection of people or the environment. Many research topics mentioned by the participants were in line with those already identified by ICRP in the paper noted above. In addition, further ideas were expressed such as, for example, that lessons learned during the COVID-19 pandemic with regards to the non-radiological social, economic and environment impacts, should be analysed for their usefulness to enhance radiological protection, and that current protection strategies and application of current radiological protection principles may need to be adapted to military scenarios like those observed recently during the military conflict in the Ukraine or the detonation of a nuclear weapon. On a broader perspective, it was discussed how radiation research and radiological protection can contribute towards the Sustainable Development Goals announced by the United Nations in 2015. This paper summarises the views expressed during the workshop and the major take home messages identified by ICRP.

Incidence risk assessment of secondary cancer due to radiotherapy of women with rectal cancer using BEIR VII, EPA, and ICRP models.

Background: Radiotherapy has a significant side effect known as radiation-induced secondary cancer. This study aims to evaluate the dose and secondary cancer risk for women with rectal cancer treated with three-dimensional conformal radiation therapy (3D-CRT) to the organs at risk (OARs) and some sensitive organs using different types of radiation-induced cancer risk prediction models, including Biological Effects of Ionizing Radiation (BEIRVII), Environmental Protection Agency (EPA) and International Commission on Radiological Protection (ICRP), and compare the results of the different models for same organs. Materials and methods: Thirty female patients with rectal cancer were considered and dose calculations were based on the PCRT-3D treatment planning system, while the radiotherapy of the patients had been performed using Shinva linear accelerator with a total dose of 45 Gy at 25 fractions. Planning target volume (PTV), OARs, and some sensitive organs were contoured, three models were used to evaluate secondary cancer risk (SCR) using the excess relative risk (ERR) and excess absolute risk (EAR). Results: The bladder presents the highest risk, in terms of ERR, and the femur head and uterus in terms of EAR from the three models (BEIR VII, EPA, and ICRP). Conclusion: Based on the obtained results, radiotherapy of rectal cancer is relatively higher for the bladder and femur head, compared to the risk for other organs, the kidney risk is significantly lower. It was observed that the SCR from the ICRP model was higher compared to BEIR VII and EPA models.

Summary of the 2021 ICRP workshop on the future of radiological protection.

The International Commission on Radiological Protection (ICRP) has embarked on a process to review and revise the current System of Radiological Protection ('the System'). To stimulate discussion, the ICRP published two open-access articles: one on aspects of the System that might require review, and another on research that might improve the scientific foundation of the System. Building on these articles, the ICRP organized a Workshop on the Future of Radiological Protection as an opportunity to engage in the review and revision of the System. This digital workshop took place from 14 October-3 November 2021 and included 20 live-streamed and 43 on-demand presentations. Approximately 1500 individuals from 100 countries participated. Based on the subjects covered by the presentations, this summary is organized into four broad areas: the scientific basis, concepts and application of the System; and the role of the ICRP. Some of the key topics that emerged included the following: classification of radiation-induced effects; adverse outcome pathway methodologies; better understanding of the dose-response relationship; holistic and reasonable approaches to optimization of protection; radiological protection of the environment; ethical basis of the System; clarity, consistency and communication of the System; application of the System in medicine and application of the principles of justification and optimization of protection.

Radiation detriment calculation methodology: summary of ICRP Publication 152.

Radiation detriment is a concept to quantify the burden of stochastic effects from exposure of the human population to low-dose and/or low-dose-rate ionising radiation. As part of a thorough review of the system of radiological protection, the International Commission on Radiological Protection (ICRP) has compiled a report on radiation detriment calculation methodology as Publication 152. It provides a historical review of the detriment calculation with details of the procedure used in ICRP Publication 103. A selected sensitivity analysis was conducted to identify the parameters and calculation conditions that can be major sources of variation and uncertainty. It has demonstrated that sex, age at exposure, dose and dose-rate effectiveness factor, dose assumption in the lifetime risk calculation, and lethality fraction have a substantial impact on the calculated values of radiation detriment. Discussions are also made on the issues to be addressed and possible ways for improvement toward the revision of general recommendations. These include update of the reference population data and cancer severity parameters, revision of cancer risk models, and better handling of the variation with sex and age. Finally, emphasis is placed on transparency and traceability of the calculation, along with the need to improve the way of expressing and communicating the detriment.

Reflections on effects of low doses and risk inference based on the UNSCEAR 2021 report on 'biological mechanisms relevant for the inference of cancer risks from low-dose and low-dose-rate radiation'.

The 2021 United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report summarises the knowledge on biological mechanisms of radiation action at low doses where, due to low statistical power of epidemiological investigations, the level of cancer risk must be inferred. It is the fourth UNSCEAR report since 1994 that looks into biological effects following low dose exposure with the aim of examining whether they support the assumption of the linear non-threshold (LNT) dose response for radiation-induced cancers. The conclusions of all four reports are affirmative. The new aspect of the 2021 report is that it focuses on the process of cancer risk inference. The aim of this article is to discuss the consequences of the conclusions regarding LNT and the possibilities of inferring risks from biological studies.

Development of alimentary tract organs for ICRP pediatric mesh-type reference computational phantoms.

In line with the activities of Task Group 103 under the International Commission on Radiological Protection (ICRP), the present study was conducted to develop a new set of alimentary tract organs consisting of the oral cavity, oesophagus, stomach, small intestine, and colon for the newborn, 1 year-old, 5 year-old, 10 year-old, and 15 year-old males and females for use in the pediatric mesh-type reference computational phantoms (MRCPs). The developed alimentary tract organs of the pediatric MRCPs, while nearly preserving the original topology and shape of those of the pediatric voxel-type reference computational phantoms (VRCPs) of ICRPPublication 143, present considerable anatomical improvement and include all micrometre-scale target and source regions as prescribed in ICRPPublication 100. To investigate the dosimetric impact of the developed alimentary tract organs, organ doses and specific absorbed fractions were computed for certain external exposures to photons and electrons and internal exposures to electrons, respectively, which were then compared with the values computed using the current ICRP models (i.e. pediatric VRCPs and ICRP-100 stylised models). The results showed that for external exposures to penetrating radiations (i.e. photons >0.04 MeV), there was generally good agreement between the compared values, within a 10% difference, except for the oral mucosa. For external exposures to weakly penetrating radiations (i.e. low-energy photons and electrons), there were significant differences, up to a factor of ∼8300, owing to the geometric difference caused by the anatomical enhancement in the MRCPs. For internal exposures of electrons, there were significant differences, the maximum of which reached a factor of ∼73 000. This was attributed not only to the geometric difference but also to the target mass difference caused by the different luminal content mass and organ shape.

Justification of dose limits-historical development, ethical basis, and the way forward.

The dose limits recommended by the International Commission on Radiological Protection have undergone considerable changes in the course of the past 90 years, and different arguments have been put forward for their justification. This has been largely due to new insights of radiation research, but changing perceptions of the related ethical values have also played a role. The current paper reviews important stages in this development and attempts to derive some implications for the Commission's next general recommendations. Above all, it suggests that it is essential to present clear and consistent justification strategies for dose limits (and related values), compatible with the core values of the system of radiological protection, especially prudence and justice.

Keeping the ICRP recommendations fit for purpose.

The International Commission on Radiological Protection (ICRP) has embarked on a review and revision of the system of Radiological Protection that will update the 2007 general recommendations in ICRPPublication 103. This is the beginning of a process that will take several years, involving open and transparent engagement with organisations and individuals around the world. While the system is robust and has performed well, it must adapt to address changes in science and society to remain fit for purpose. The aim of this paper is to encourage discussions on which areas of the system might gain the greatest benefit from review, and to initiate collaborative efforts. Increased clarity and consistency are high priorities. The better the system is understood, the more effectively it can be applied, resulting in improved protection and increased harmonisation. Many areas are identified for potential review including: classification of effects, with particular focus on tissue reactions; reformulation of detriment, potentially including non-cancer diseases; re-evaluation of the relationship between detriment and effective dose, and the possibility of defining detriments for males and females of different ages; individual variation in the response to radiation exposure; heritable effects; and effects and risks in non-human biota and ecosystems. Some of the basic concepts are also being considered, including the framework for bringing together protection of people and the environment, incremental improvements to the fundamental principles of justification and optimisation, a broader approach to protection of individuals, and clarification of the exposure situations introduced in 2007. In addition, ICRP is considering identifying where explicit incorporation of the ethical basis of the system would be beneficial, how to better reflect the importance of communications and stakeholder involvement, and further advice on education and training. ICRP invites responses on these and other areas relating to the review of the System of Radiological Protection.

Lung cancer risk and effective dose coefficients for radon: UNSCEAR review and ICRP conclusions.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has provided a detailed and authoritative update of its reviews of the epidemiology and dosimetry of radon and progeny. Lifetime risk of lung cancer calculated using data for several miner cohorts were 2.4-7.5 × 10-4per working level month (WLM) of radon-222 progeny exposure for a mixed male/female population and 3.0-9.6 × 10-4per WLM for a male population. Dosimetric models gave mean values of effective dose coefficients from radon-222 progeny of 12 mSv per WLM for mines, 16 mSv per WLM for indoor workplaces and 11 mSv per WLM for homes. The lifetime risk coefficient used by the International Commission on Radiological Protection (ICRP) is 5 × 10-4per WLM and it has recently recommended an effective dose coefficient for radon-222 and progeny of 3 mSv per mJ h m-3(about 10 mSv per WLM) for most circumstances of exposure. The ICRP risk and dose coefficients are supported by the UNSCEAR review and provide a clear and firm basis for current international advice and standards for protection from radon. Notwithstanding this evidence and the ICRP advice, UNSCEAR will continue to use a lower value of effective dose coefficient of 5.7 mSv per WLM for assessments of population exposures.

Development of paediatric mesh-type reference computational phantom series of International Commission on Radiological Protection.

Very recently, Task Group 103 of the International Commission on Radiological Protection (ICRP) completed the development of the paediatric mesh-type reference computational phantoms (MRCPs) comprising ten phantoms (newborn, one year-old, five year-old, ten year-old, and fifteen year-old males and females). The paediatric MRCPs address the limitations of ICRPPublication 143's paediatric reference computational phantoms, which are in voxel format, stemming from the nature of the voxel geometry and the limited voxel resolutions. The paediatric MRCPs were constructed by converting the voxel-type reference phantoms to a high-quality mesh format with substantial enhancements in the detailed anatomy of the small and complex organs and tissues (e.g. bones, lymphatic nodes, and extra-thoracic region). Besides, the paediatric MRCPs were developed in consideration of the intra-organ blood contents and by modelling the micron-thick target and source regions of the skin, lens, urinary bladder, alimentary tract organs, and respiratory tract organs prescribed by the ICRP. For external idealised exposures, the paediatric MRCPs provide very similar effective dose coefficients (DCEs) to those from the ICRP-143 phantoms but significantly different values for weakly penetrating radiations (e.g. the difference of ∼20 000 times for 10 keV electron beams). This paper introduces the developed paediatric MRCPs with a brief explanation of the construction process. Then, it discusses their computational performance in Geant4, PHITS, and MCNP6 in terms of memory usage and computation speed and their impact on dose calculations by comparing their calculated values of DCEs for external exposures with those of the voxel-type reference phantoms.

Reflection on the proposed changes to dose quantities-an industrial perspective.

In 2021, the ICRP initiated the revision of the general recommendations of the system of radiation protection, and part of it will focus on dose quantities. The recently published ICRP Publication 147 and ICRU Report 95 have described the extent of the proposed modifications and paved the way for the strategy to be adopted. These revisions would seek to simplify, improve the accuracy and extend the field of use of dose quantities. While the Radiological Protection Working Group of the World Nuclear Association recognises the notable improvement in the estimation of the protection quantities and the usefulness of such changes for the medical and research sector, the benefits of the proposed new system seem very limited for the nuclear industry and industries involving naturally occurring radioactive materials. The complexity associated with changing a long-standing and robust system and the risk incurred by the human factor seem unjustified, bearing in mind the likely cost.

Quantitative evaluation of conservatism in the concept of committed dose from internal exposure for radiation workers.

For compliance with dose limits, the International Commission on Radiological Protection (ICRP) recommends that the committed dose be assigned to the year in which radionuclide intake occurred in the case of internal exposure. For radiation workers, the committed dose is evaluated over the 50 year period following the intake, which is a rounded value for the working-life expectancy of a young person entering the workforce. In this study, we develop an approach to the quantitative evaluation of the conservatism in the concept of the committed dose from internal exposure for radiation workers from the viewpoint of radiological risk. Actual annual doses due to an intake of radionuclides for strontium-90 (90Sr), caesium-137 (137Cs), and plutonium-239 (239Pu) were simulated. Risks of fatal cancer, i.e. unconditional death probability rates, were calculated in accordance with the risk estimation method in ICRP Publication 60. It was found that the conservatism ranged from 1.1 to 1.6 for90Sr, 1.0 to 1.6 for137Cs, and 1.6 to 2.2 for239Pu. The importance of understanding the extent of this conservatism and the uncertainty for practical radiological protection are also discussed.

Development of skeletal systems for ICRP pediatric mesh-type reference computational phantoms.

In 2016, the International Commission on Radiological Protection (ICRP) launched Task Group 103 (TG 103) for the explicit purpose of developing a new generation of adult and pediatric reference computational phantoms, named 'mesh-type reference computational phantoms (MRCPs)', that can overcome the limitations of voxel-type reference computational phantoms (VRCPs) of ICRPPublications 110and143due to their finite voxel resolutions and the nature of voxel geometry. After completing the development of the adult MRCPs, TG 103 has started the development of pediatric MRCPs comprising 10 phantoms (male and female versions of the reference newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old). As part of the TG 103 project, within the present study, the skeletal systems, one of the most important and complex organ systems of the body, were developed for each phantom age and sex. The developed skeletal systems, while closely preserving the original bone topology of the pediatric VRCPs, present substantial improvements in the anatomy of complex and/or small bones. In order to investigate the dosimetric impact of the developed skeletons, the average absorbed doses and the specific absorbed fractions for radiosensitive skeletal tissues (i.e. active marrow and bone endosteum) were computed for some selected external and internal exposure cases, which were then compared with those calculated with the skeletons of pediatric VRCPs. The comparison result showed that the dose values of the pediatric MRCPs were generally similar to those of the pediatric VRCPs for highly penetrating radiations (e.g. photons >200 keV); however, for weakly penetrating radiations (e.g. photons ⩽200 keV and electrons), significant differences up to a factor of 140 were observed.

The use of dose quantities in radiological protection: ICRP publication 147 Ann ICRP 50(1) 2021.

The International Commission on Radiological Protection has recently published a report (ICRP Publication 147;Ann. ICRP50, 2021) on the use of dose quantities in radiological protection, under the same authorship as this Memorandum. Here, we present a brief summary of the main elements of the report. ICRP Publication 147 consolidates and clarifies the explanations provided in the 2007 ICRP Recommendations (Publication 103) but reaches conclusions that go beyond those presented in Publication 103. Further guidance is provided on the scientific basis for the control of radiation risks using dose quantities in occupational, public and medical applications. It is emphasised that best estimates of risk to individuals will use organ/tissue absorbed doses, appropriate relative biological effectiveness factors and dose-risk models for specific health effects. However, bearing in mind uncertainties including those associated with risk projection to low doses or low dose rates, it is concluded that in the context of radiological protection, effective dose may be considered as an approximate indicator of possible risk of stochastic health effects following low-level exposure to ionising radiation. In this respect, it should also be recognised that lifetime cancer risks vary with age at exposure, sex and population group. The ICRP report also concludes that equivalent dose is not needed as a protection quantity. Dose limits for the avoidance of tissue reactions for the skin, hands and feet, and lens of the eye will be more appropriately set in terms of absorbed dose rather than equivalent dose.