THE COMPLEXITY OF QUANTITIES IN RADIATION DOSIMETRY: THE ISSUE OF RADIATION QUALITY.

When Harald Rossi developed a new radiation measurement instrument more than 60 years ago-the tissue equivalent low-pressure proportional counter, also called Rossi Counter-his initial intention was to provide a technique to measure LET. He realized soon that the measurements provided insight into the stochastic nature of the interactions of ionizing radiation with matter and that the measured results represented an alternative to characterize radiation quality in terms of stochastic or microdosimetric quantities. Progress in cellular and molecular radiation biology and in simulating charged particle tracks in biological entities are now essential features and have extended the original delineation of the field of microdosimetry. This general field of microdosimetry, as part of an interdisciplinary approach for the study of molecular mechanisms and cellular radiation effects, continues to be an important area of radiation research, documented by 13 previous Microdosimetry Symposia and, again, at this Symposium. However, the quantification of radiation quality remains a subject of practical importance. In fact, the issue has gained in importance due to the application of ions for therapy and due to the need for protection from exposures to complex and high-energy radiation fields, for example, to cosmic radiation in civil aviation and space missions. In practice pragmatic, empirical approaches are being used which has led to a complex set of dosimetric quantities and terms.

The 42nd Lauriston S. Taylor Lecture: Radiation Dosimetry Research for Medicine and Protection-A European Journey.

The assessment of doses related to exposures to ionizing radiation is an essential part of all applications of ionizing radiation including radiation medicine, radiation protection, radiation biology, radiation epidemiology, and also industrial uses of radiation. Absorbed dose is generally considered to be the fundamental quantity of radiation dosimetry. It is a metrologically sound quantity for which even primary standards exist for some materials, and it is used routinely in practice. However, there is no unique correlation between absorbed dose and the radiation-induced biological effect considered. There are also different objectives of radiation dosimetry for different applications. In radiation protection, quantities are required to set meaningful exposure limits and to implement the principle of optimization. In radiation therapy, the dependence of clinical outcomes on temporal aspects of the irradiations must be accounted for. In radiation diagnostics, quantities are needed to enable and monitor optimization of radiation dose and image quality. In radiation protection and in therapy with high linear-energy-transfer radiations, appropriate methods and parameters are needed to account for differences in radiation quality. These limitations of the quantity absorbed dose have led to the use of a multiplicity of dose quantities and dose modification factors. Radiation dosimetry continues, therefore, to be a field of active research regarding fundamental and conceptual aspects, taking account of advances in technologies, of novel methods in radiation therapy and diagnostics, and of progress in computational dosimetry. Dosimetry of high-energy radiations such as cosmic radiation encountered at flight altitudes and during space missions as well as at high-energy accelerators has become an important issue. In Europe, collaboration and coordination of radiation research in general, and dosimetry research in particular, are playing an important role. Dedicated research programs of the European Commission have been and still are very valuable and include collaborations with institutes in Eastern Europe and non-European countries. Several current and recent research topics in radiation dosimetry are addressed based on research carried out within European research programs, at European research centers including the European Organization for Nuclear Research (known as CERN), in European particle therapy projects, and at national metrological institutes. One focus is the quantification of radiation quality in radiation protection and in high linear-energy-transfer radiation therapy with emphasis on measurements with low-pressure proportional counters. Another focus is dosimetry of high-energy radiations with respect to measurements of cosmic radiation and at CERN's high-energy accelerators.

Overview of the ICRP/ICRU adult reference computational phantoms and dose conversion coefficients for external idealised exposures.

This paper reviews the ICRP Publications 110 and 116 describing the reference computational phantoms and dose conversion coefficients for external exposures. The International Commission on Radiological Protection (ICRP) in its 2007 Recommendations made several revisions to the methods of calculation of the protection quantities. In order to implement these recommendations, the DOCAL task group of the ICRP developed computational phantoms representing the reference adult male and female and then calculated a set of dose conversion coefficients for various types of idealised external exposures. This paper focuses on the dose conversion coefficients for neutrons and investigates their relationship with the conversion coefficients of the protection and operational quantities of ICRP Publication 74. Contributing factors to the differences between these sets of conversion coefficients are discussed in terms of the changes in phantoms employed and the radiation and tissue weighting factors.

Radiological protection issues arising during and after the Fukushima nuclear reactor accident.

Following the Fukushima accident, the International Commission on Radiological Protection (ICRP) convened a task group to compile lessons learned from the nuclear reactor accident at the Fukushima Daiichi nuclear power plant in Japan, with respect to the ICRP system of radiological protection. In this memorandum the members of the task group express their personal views on issues arising during and after the accident, without explicit endorsement of or approval by the ICRP. While the affected people were largely protected against radiation exposure and no one incurred a lethal dose of radiation (or a dose sufficiently large to cause radiation sickness), many radiological protection questions were raised. The following issues were identified: inferring radiation risks (and the misunderstanding of nominal risk coefficients); attributing radiation effects from low dose exposures; quantifying radiation exposure; assessing the importance of internal exposures; managing emergency crises; protecting rescuers and volunteers; responding with medical aid; justifying necessary but disruptive protective actions; transiting from an emergency to an existing situation; rehabilitating evacuated areas; restricting individual doses of members of the public; caring for infants and children; categorising public exposures due to an accident; considering pregnant women and their foetuses and embryos; monitoring public protection; dealing with 'contamination' of territories, rubble and residues and consumer products; recognising the importance of psychological consequences; and fostering the sharing of information. Relevant ICRP Recommendations were scrutinised, lessons were collected and suggestions were compiled. It was concluded that the radiological protection community has an ethical duty to learn from the lessons of Fukushima and resolve any identified challenges. Before another large accident occurs, it should be ensured that inter alia: radiation risk coefficients of potential health effects are properly interpreted; the limitations of epidemiological studies for attributing radiation effects following low exposures are understood; any confusion on protection quantities and units is resolved; the potential hazard from the intake of radionuclides into the body is elucidated; rescuers and volunteers are protected with an ad hoc system; clear recommendations on crisis management and medical care and on recovery and rehabilitation are available; recommendations on public protection levels (including infant, children and pregnant women and their expected offspring) and associated issues are consistent and understandable; updated recommendations on public monitoring policy are available; acceptable (or tolerable) 'contamination' levels are clearly stated and defined; strategies for mitigating the serious psychological consequences arising from radiological accidents are sought; and, last but not least, failures in fostering information sharing on radiological protection policy after an accident need to be addressed with recommendations to minimise such lapses in communication.

The state of radiological protection; views of the radiation protection profession: IRPA13, Glasgow, May 2012.

The IRPA13 Congress took place from 14-18 May 2012 in Glasgow, Scotland, UK, and was attended by almost 1500 radiological protection professionals. The scientific programme of the Congress was designed to capture a snapshot of the profession's views of the current state of knowledge, and of the challenges seen for the coming years. This paper provides a summary of these results of the Congress in twelve key scientific areas that served as the structural backbone of IRPA13.

Dosimetric quantities in radiological protection and risk assessment.

Central to the application of the system of protection recommended by the International Commission on Radiological Protection (ICRP) are the physical quantity, absorbed dose, and the protection quantities, equivalent and effective dose. These protection quantities are used to set dose limits, constraints and reference levels and to test compliance in the various activities of occupational and public exposure. They are also used in the assessment of doses from medical procedures. Effective dose in particular has proved to be a very valuable quantity that allows the summation of doses from external radiation and internal doses from different radionuclides in a single risk-related value. However, while it is possible to measure external radiation exposures and estimate internal exposures down to very low levels of dose, the associated risks, principally of cancer, are much less certain. Equivalent and effective doses are calculated using simplifying assumptions to apply to reference workers and members of the public for the purpose of control of exposures. Risks to individuals or specific population groups should be calculated not using these quantities but using best scientific information. The purpose of this note is to provide a short and readily accessible account of the purpose of the ICRP dosimetric quantities, how they are calculated, how they should be used, and how they relate to risk estimation.