In London in 1925, at the first International Congress of Radiology (ICR), the predecessor to the International Commission on Radiation Units and Measurements (ICRU) was created as the International X-ray Unit Committee. The International X-ray and Radium Protection Committee, predecessor to the International Commission on Radiological Protection (ICRP), was created in Stockholm in 1928 at the second ICR. Thus, ICRP and ICRU have a shared origin and many common interests.
Although both organisations function independently, until the 1970s they usually met at the time and place of the ICR. They shared (and still share) many interests and, at times, many members including Lauriston Taylor, a pioneer and giant in the field of radiological protection.
This publication represents a renewed collaboration between the two organisations, being the first in a series of planned joint efforts, with contributions from members of both ICRP and ICRU. In this case, ICRP has taken the lead, while ICRU will take the lead for some of the forthcoming publications.
In addition, this report is vital to the full implementation of the 2007 Recommendations of ICRP (ICRP, 2007). The Recommendations formally define ‘reference phantoms’ as ‘voxel phantoms for the human body…’. The current report delivers the most important of these voxel phantoms: the adult male and adult female.
Practical radiological protection for workers and the general public uses dosimetric quantities which quantify the exposure to ionising radiation appropriately for the implementation of the fundamental principles of limitation and optimisation. Radiation protection regulations and guidelines for demonstration of compliance are formulated in terms of reference or standard individuals. ICRP and ICRU have established a system of protection and operational dosimetric quantities which are based on reference data, models, and phantoms, and which have been shown to provide a satisfactory conceptual and practicable procedure for risk management of the low dose exposures of concern in radiological protection.
It was recognised long before the introduction of the current system of protection and operational quantities that exposure assessment and monitoring of humans exposed to ionising radiation from external sources and from incorporated radionuclides requires the use of models and phantoms characterizing reference individuals. This led to the development of phantoms, i.e. physical models of the human body such as the ‘Rando’ phantom (Alderson et al., 1962), and computational anthropomorphic models such as the MIRD model (Fisher and Snyder, 1967) which mathematically described the geometries of the body and its organs.
This important facet of radiation dosimetry has also been an important part of the work by ICRP and ICRU.
ICRP first presented data on standard man in ICRP Publication 2 Report of Committee II on Permissible Dose for Internal Radiation (ICRP, 1960) as it formulated the concept of permissible doses for workers from incorporated radionuclides. In 1975, ICRP Publication 23 on Reference Man (ICRP, 1975) was published. It contained comprehensive information on anatomical, morphological, and physiological data, and provided a systematic and consistent set of reference data for reference individuals. The most recent publication on this subject, and replacing ICRP Publication 23, is ICRP Publication 89 (ICRP, 2002), which provides reference values for both male and female subjects of six different ages from newborn to adult.
One of ICRU’s objectives is to provide guidance on radiation measurements in all areas of application of ionising radiation. So-called standard phantoms for radiotherapy applications were introduced in ICRU Report 10d (ICRU, 1963) and ICRU Report 23 (ICRU, 1973). These phantoms have simple geometry, e.g. cubic water phantoms used to compare measurements under standard conditions of irradiation. For the definition of operational quantities, ICRU introduced a reference computational phantom, the ICRU sphere, 30-cm diameter, composed of ICRU tissue (ICRU, 1980). ICRU Report 48 (ICRU, 1992) was a review on phantoms and computational models in therapy, diagnosis, and protection.
In this joint ICRP/ICRU report, reference computational phantoms of the adult male and adult female are introduced. These phantoms will be for use by ICRP and ICRU to derive organ dose conversion coefficients for external and internal exposure, following the revisions introduced in ICRP Publication 103 (ICRP, 2007).
These phantoms were also constructed to be consistent with the external dimensions and masses of organs and tissues in ICRP Publication 89 and thus are complementary to that document. The reference phantoms are voxel based and have been derived from tomographic imaging data of a male and female patient. Thus, they reflect an anatomically realistic spatial distribution of organs and tissues with a high degree of consistency with the reference values in ICRP Publication 89. Furthermore, the technique applied in the construction of the phantoms from the medical imaging, as described in some detail in the report, also permitted the identification of all organs and tissues, including those explicitly noted in the definition of effective dose, thus enabling the full implementation of the recommendations in Publication 103 with regard to the reference dose conversion coefficients. The treatment of the anatomical properties of the skeleton in these reference phantoms will allow detailed skeletal dosimetry to be performed and deserves special mention. Reference organ conversion coefficients for exposure to incorporated radionuclides will, of course, be evaluated using ICRP reference biokinetic and dosimetric models, including an update of the Publication 66 (ICRP, 1994) Human Respiratory Tract Model, and the Publication 100 (ICRP, 2006) Human Alimentary Tract Model.
All reference dosimetric data used for dosimetry, dose assessment, and monitoring in radiological protection for exposure of adults will, in the future, be based on calculations and evaluations using these reference phantoms. Reference phantoms for persons of younger ages are in the process of being prepared using a similar approach; in particular, consistency with ICRP Publication 89 will be assured.
In recent years, a number of computational phantoms have been published by various authors for a variety of purposes and applications based on tomographic imaging data of individuals. The principal purpose of the phantoms presented here is in the evaluation of reference dosimetric data by ICRP and ICRU, in particular reference organ dose conversion coefficients, thus enabling the determination of effective dose. In spite of this intended limited application, the report also contains a CD with the phantoms and guidance regarding how to use these phantoms in radiation transport calculations. Thus, the phantoms can also be used for other applications. However, any other application must respect the manner of construction of these particular phantoms and their relationship to the reference anatomical data of ICRP Publication 89. In particular, it must be remembered that the phantoms represent reference persons, and any potential application with regard to a particular individual can be associated with substantial uncertainties.
Hans-Georg Menzel (ICRP/ICRU)
Christopher Clement (ICRP)
Paul DeLuca (ICRU)
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