10 Conclusions and Recommendations

Abstract

There exists a variety of methods that are currently under development, and/or have been suggested, for emergency dosimetry following acute exposure to radiation after a radiological incident. The main methods can be classified as biodosimetry and physical dosimetry and can be performed on biological materials (primarily blood), physical (nonbiological) materials, or materials that are biologically derived (teeth, bone, nails). In addition, these methods can be supplemented by neutron activation measurements (if a neutron dose is suspected) and/or bioassays (if internal contamination is suspected). Radiation field mapping and “time and motion” studies are also useful in many circumstances. Choice of method depends on the number of affected individuals, the type of radiation exposure, and whether or not the individual may have suffered internal radiological contamination as well as external irradiation. (It can be assumed that all affected individuals will have been externally exposed.) The choice of method also depends on the goal of the measurement. If the goal is rapid screening to determine approximately the level of individual exposure, then the methods selected may or may not be the same as those methods chosen for more detailed follow-up. The former methods might be used for triage purposes, whereas the latter may be used to assist medical practitioners in determining the most appropriate interventional medical therapy. A review and analysis of the various biological and physical dosimetry methods reveals a range of maturity levels for the various techniques. Some are of such maturity as to allow immediate application in the event of a largescale exposure. Primarily these are biodosimetry methods, for example, dicentric chromosome assay (DCA) and cytokinesis-block micronucleus (CBMN) assay. In contrast, many of the physical dosimetry methods are still under development. Based on laboratory intercomparisons, optically stimulated luminescence (OSL) of electronic components is possibly the closest to real-world application. Other methods [e.g., thermoluminescence (TL)] and other target materials (e.g., smartphone glass) are still under experimental laboratory testing. Electron paramagnetic resonance (EPR) of biologically derived material (e.g., teeth) is well developed for in-vitro analysis, but not yet for in-vivo analysis. Electron paramagnetic resonance analysis of finger and toe nails is not yet ready for widespread application, despite some efforts to date in small-scale accidents. None of the bioor physical dosimetry methods by themselves are able to distinguish between internal and external exposure. Combinations of methods might be able to indicate that an internal dose component is present, but confirmation would be necessary with bioassays. Similarly, the above techniques are not yet able to distinguish neutron dose from photon dose, and in addition several of the methods have low sensitivity to neutron exposure. Thus, when neutron exposure is suspected and neutron-gamma distinction is required, the only currently available technique is neutron activation analysis in combination with one of the above methods. The emphasis of this Report has been on dosimetry during the initial phase following acute radiation exposure. As a result, the focus has been on dosimetry for deterministic effects and the measured quantity of interest is absorbed dose. It is necessary to distinguish between the quantity measured by physical dosimetry methods and that measured by biological methods. If calibration of the dosimeters used in the measurements is with penetrating, energetic photons, and if the individuals are exposed also to penetrating photons during the radiological incident, then RBE ~1 and there is no difference in the quantity measured with the 2 types of dosimetry. If one of these conditions is not met, however, the quantities measured must be considered different, depending on the value of the RBE. Knowledge of the RBE thus becomes important. The second important distinction between biodosimetry and physical dosimetry is that the former examines dose to the person, whereas the latter examines dose to some object close to (e.g., phone) or part of (e.g., teeth) the person. Differences in the dose evaluated using these 2 methods should be expected, even if the RBE value is ~1. Nevertheless, for triage measurements at least, the distinction between the quantities and values measured with physical and biodosimetry methods should not be weighed during triage consideration and may be ignored. Furthermore, the absorbed dose (in Gy) should be the quoted value and the quantity of interest. Calculations and estimates of the RBE and radiological and organ weighting factors (for effective dose estimates) may follow only if warranted for medical management and may be considered in follow-up measurements and calculations. 893186 CRUXXX10.1177/1473669119893186Journal of the ICRU XX(X)Conclusions and Recommendations research-article2020