Full Reference: ICRP 2022. Radiation detriment calculation methodology. ICRP Publication 152. Ann. ICRP 51 (3)
Publisher: SAGE Publication, UK
Price: UK £183.75 (Online)
The International Commission on Radiological Protection’s Publication 152 (ICRP Publication 152) entitled “Radiation Detriment Calculation Methodology” was published in 2022 by SAGE Publications, UK. As described by the ICRP, this Publication is part of a thorough review launched by it on the System of Radiological Protection following ICRP Publication 103 published in 2007. Publication 152 provides a historical review of the radiation detriment calculation methodology since ICRP Publication 26 (1977) for the purpose of radiological protection. The concept of radiation detriment was introduced by the ICRP in its Publication (1973) which has been developed further by it over the last few decades.
The ICRP defines radiation detriment as the excess of stochastic health effects in a group of individuals exposed to low-level radiation and their descendants compared with a nonexposed group. It is determined from sex-averaged and age-at-exposure-averaged lifetime risk estimates for a set of organs and tissues, taking into account the severity in terms of quality of life in nonlethal conditions and length of life lost. The ICRP notes that although the current scheme of radiation detriment calculation is well established, it needs to evolve to better reflect changes in population health statistics and progress in scientific understanding of radiation health effects. In this regard, update on parameters such as the reference population data and cancer severity and some improvement in cancer risk models based on the accumulation of recent epidemiological findings have been carried out. The update in this Publication should be considered an improved and corrected version of Annex A.4 of Publication 103.
Radiation detriment was defined initially as the mathematical “expectation” of harm incurred in a group from radiation exposure (ICRP, 1973, 1977a). The harm in this definition was intended to encompass deleterious effects of all sorts, including the socioeconomic impact. However, only health effects were considered in practice, and hence, detriment was expressed as the expected value of the weighted number of health effects to be experienced by the group. Detriment was redefined in Publication 60 (ICRP, 1991) as a multidimensional concept that can be expressed in a variety of ways depending on the purpose. At the same time, the ICRP continued efforts to aggregate different aspects of detriment into a single quantity, and the methodology was further refined in Publication 103 (ICRP, 2007). It is currently defined as the excess of stochastic health effects in a group of individuals exposed to low-level radiation and their descendants compared with a nonexposed group. It is determined from sex-averaged and age-at-exposure-averaged lifetime risk estimates for a set of organs and tissues, taking into account the severity in terms of quality of life in nonlethal conditions and length of life lost.
Publication 152 is divided into six sections comprising 103 pages, including the abstract, executive summary, references, and the annexure. Section 1 is “Introduction” which provides the background and need for bringing out the current publication. Scope and objective have been elaborated in this section, along with the structure of the Publication. Section 2 entitled “Historical Development” provides a review of the quantitative expression of radiation detriment starting from ICRP 26 (1977). It specifically describes earlier ICRP Publications dealing with the subject, namely ICRP Publications 27 (1977), 45 (1985), 60 (1991), and 103 (2007), and highlights how the calculation method has adapted to progress in scientific knowledge. It especially brings out the modifications incorporated in Publication 103 (ICRP, 2007) in terms of the adoption of a new detriment calculation methodology as compared to ICRP 60 (1991). One major change in ICRP 103 was the move to nominal risk calculation based on cancer incidence data rather than cancer mortality data. For clarification, the detriment calculated using this methodology is specifically called “radiation detriment,” and the term “detriment” means radiation detriment hereafter unless otherwise noted.
Section 3 “Calculation of Radiation Detriment” is, to my mind, the most important section of this publication. It first details the computation process used in Publication 103 (ICRP, 2007) and then points out the programming errors in the calculations of the nominal risk coefficients in it. Despite a considerable increase in the nominal risk coefficients of bone marrow, breast, and ovarian cancers due to recalculations, it is shown that impact on overall nominal risk is limited (4%). Data sources, risk models, computational methods, and the rationale for the parameter values adopted are explained for each step of the process. In Publication 103, nominal risks were calculated based on cancer incidence, using the most up-to-date information at the time. Nevertheless, when adjusted for severity, the resulting detriment values were quite similar to those in Publication 60 (ICRP, 1991). It was, therefore, concluded that the approximated overall fatal risk coefficient of 5% per Sv on which international radiation safety standards were based continued to be appropriate for the purposes of radiological protection. It is demonstrated that the correction of errors does not change this conclusion. Therefore, the ICRP concluded that the miscalculations of the nominal risk coefficients and radiation detriments have no implications for operation of the System of Radiological Protection.
Section 4 “Sensitivity of Radiation Detriment Calculation” presents the interesting results of a series of sensitivity analyses that examined the impact of selected parameters on radiation detriment. The aim of the analysis was to identify major sources of variation and uncertainty in the calculation of radiation detriment. The analysis found that parameters of substantial impact on radiation detriment are sex, age at exposure, dose rate effectiveness factor (DDREF), dose assumption, and lethality fraction. The parameters with the least impact are lifetime risk metric, minimum latency period, maximum attained age, and minimum QOL factor. Section 5 “Potential Evolution” discusses ways to identify the issues and possible ways to provide directions for the future evolution of radiation detriment, which could be a crucial part in the development of the Commission’s General Recommendations. Section 6 “Summary and Conclusions” summarizes the main conclusions, and includes suggestions for future improvement. It points out that radiation detriment needs to evolve depending on changes in cancer incidence and survival rates, and on advances in scientific understanding of radiation health effects. Further, it suggests that a full description of calculation steps and development of open-source software for calculating radiation detriment is necessary to improve transparency. It is also desirable to improve the way, in which radiation detriment is expressed and communicated so that nonspecialists can have a balanced perspective on the health risks of radiation, the ICRP points out. Annexure A of Publication 152 provides the updated baseline and demographic data in the form of seven tables.
One aspect of Publication 152 that stands out is its comprehensibility despite dealing with a complex subject. The calculations and analyses described with graphs and tables aid in the transparency and comprehensibility of the document. The Publication can serve as a valuable and authentic resource material for medical physics practitioners and students and for all those interested in research, teaching, and practice in the area of radiological protection. The cost of the international paperback edition of the Publication is £183.75 from SAGE Publishing as found on the Internet (link: https://uk.sagepub.com/en -gb/eur/icrp-publication-152-radiation-detriment - calculation-methodology/book284987). As per the ICRP policy since 2018, all issues of Annals of the ICRP are free to access other than the current and the two most recent volumes.