The definition of appropriate quantities, and their associated units, is a fundamental necessity for any scientific activity and for any practical application of scientific knowledge. In 1950, ICRU expanded its original mandate given by ICR for providing an internationally agreed upon unit for measurement of radiation as applied in medicine, to a wider field including the areas of fundamental metrology, radiation biology, and the radiation science at large, extending from industrial application to the radiation protection of humans and the environment.

ICRU has continued to recommend new quantities and units as the need arose, after the proposal of the roentgen in 1928, for example, the absorbed dose (1950), the rad (1953), the fluence (1962), the kerma (1968), and the cema (1998). Specifically, for application in radiation protection the quantity “dose equivalent” was introduced in 1962 [jointly with the International Commission on Radiological Protection (ICRP)] which is defined as a product of absorbed dose and a quality factor which takes into account the radiation quality empirically.

Defining the quantities and units for ionizing radiation represent the most basic element of the core mission of the Commission. ICRU’s only Standing Committee is on Fundamental Quantities and Units for Ionizing Radiation. The work of this Committee is evidenced by the Series of six ICRU reports on Fundamental Quantities and Units, the first, Report 10a was published in 1962 and last was Report 85a in 2011. Along his line, ICRU is also involved in the process of implementing its own recommendations, in particular for quantities and units. One important aspect is that ICRU is member of the Consultative Committee for Ionizing Radiation and the Consultative Committee for Units, which reports to the International Committee for Weights and Measures (CIPM). ICRU is, thus, an active member of the International Organization of General Metrology. Furthermore, ICRU maintains liaison with the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), and the International Atomic Energy Agency (IAEA) all of which are key players in the practical implementation of quantities and units, and in developing and publishing international standards for the use of ionizing radiation.

Another focus of ICRU is to provide guidance, recommendations, and reference physical data for radiation measurements, especially for radiation dosimetry; the first Report 10b (1964) was on Physical Aspects of Irradiation and the last Report 80 (2008) on Dosimetry Systems for Use in Radiation Processing.

Last, good (dosimetry) measurements also require good basic physical data and reference values. ICRU has seen as its responsibility to keep up-to-date with the progress of science in order to provide such data regularly. Examples for basic physical data include Report 31 (1979) on Average Energy Required to Produce an ion Pair, reports on stopping powers such as Reports 37 (1984), 39 (1985), 64 (2001), 71 (2005), and 90 (2016), and Reports on reference data such as Reports 44 (1989), 46 (1989), 77 (2007), and 84 (2010).