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Excerpt from "Rigour Within UncertaintyóAn Unfinished Quest: ICRP and High-LET Radiations"

Ralph H. Thomas

Note: On April 15, 2005, Ralph Thomas presented a talk at the Thirteenth Annual J. Newell Stannard Lecture Series held in Sacramento, CA. The following excerpt includes the abstract and preface of Dr. Thomas's talk. The full text is available here.


The development of the current International Commission on Radiological Protection (ICRP) quantities are described and the difficulties with the application of these quantities to high-linear-energy-transfer (LET) radiations are discussed. Difficulties with the current recommendations of the commission are discussed and a critique given of the "Draft for Consultation: 2005 Recommendations of the International Commission on Radiological Protection." Suggestions for its improvement are made.


Five years ago the author wrote in a paper presented to the Ettore Majorana Centre for Scientific Culture in Erice: "At the outset of any paper on radiation protection dosimetry it is appropriate to acknowledge the crucial roles played by both the ICRP and ICRU [International Commission on Radiation Units and Measurements] in defining and establishing internationally and generally accepted quantities for use in radiological protection. The international acceptance of very similar radiation protection standards has truly been a triumph by ICRP.

"However, there are omens that all is not well with this international accord. Some countries . . . have been slow to take up the recommendations of ICRP Publication 60. . . . There are complex reasons . . .[which] might include . . . disbelief in the interpretation of the basic sciences behind the recommendations of ICRP. . . . The suggestion that there is scepticism of the ICRP recommendations is troubling because it is to some degree true. This scepticism must be dispelled if the general international agreement on radiation protection standards is to be maintained" (Thomas 2001).

On re-reading this text in 2005 the author is confirmed in these opinions and believes them to be still true today. It is therefore vital to make every effort to re-establish the international consensus on the scientific bases for the foundations for, and acceptance of, very similar radiation protection standards that had been evident prior to the publication of the commissionís recommendations in 1991 (Publication 60). An opportunity to achieve this goal is afforded by the current review by the ICRP of its fundamental recommendations.

In 2001 ICRP announced that it was to undertake a major revision of its current recommendations (ICRP 1991), including its dosimetric quantities. In April of that year, the chairman of the ICRP spoke in Bethesda to some members of the National Council on Radiation Protection and Measurements (NCRP) of the new openness in the method by which ICRP recommendations are to be reached. The commission is to be congratulated on its sentiment that it "wishes there to be an ongoing debate with an iteration of ideas . . ." (ICRP 2001). This openness has afforded an opportunity for those individuals who make use of recommendations of the ICRP to address some of the issues already discussed in the literature, providing them an opportunity to interact effectively with the ICRP by pointing out difficulties with the status quo and to suggest improvement in the commissionís recommendations. The commission is to be thanked for providing the opportunity and privilege of commenting on its draft for consultation. This act of Glasnost is most welcome and to be highly commended (Thomas et al. 2002).

Since 1991 the scientific literature has revealed concerns with some aspects of ICRP 60, particularly by dosimetrists interested in the measurement of high-energy and high-LET radiations in general and neutrons in particular (for bibliographies see ICRP 1997; ICRU 1998; Thomas 1998-2004). Roger Clarke, chairman of ICRP, has agreed that "there have been some persistent difficulties with, and misunderstandings of, the definitions of the Commissionís dosimetric quantities. The Commission will remove these by clarifying its definitions and specifying their application" (Clarke 2003).1

As part of the commissionís review it has issued ICRP Publication 92 entitled "Relative Biological Effectiveness (RBE), Quality Factor (Q), and Radiation Weighting Factor (wR)" (ICRP 2003). This is clearly an important document and might have been influential in formulating the commissionís final recommendations but its advice appears only to have been partially adopted in the draft for consultation (see following paragraph).

In the autumn of 2004 the commission posted on its website its "Draft for Consultation: 2005 Recommendations of the International Commission for Radiological Protection" (hereinafter referred to as the draft for consultation) and invited both institutional and individual comment (ICRP 2004).

The current status of the review may be found on the website of the ICRP and in summary is as follows: "The public consultation on the draft Recommendations of the ICRP is now completed, and ICRP is delighted to report that we have had an overwhelming response with detailed and very constructive proposals from organisations and individuals all over the world. ICRP intends to consult in the near future on the 'foundation documents' underpinning the Recommendations. Comments on the 'foundation documents' will also be taken into account in the review and revision of the draft Recommendations. Depending on the outcome of the review process, a second, shorter round of consultation on an updated draft may be necessary" (ICRP 2005).

1For more than 25 years (1968-1996) the author was an active participant in the work of both the ICRP and ICRU including participation in the drafting of many of the reports cited in this paper. For the past eight years he has written several papers attempting to correct inconsistencies on the part of ICRP. He therefore takes his share of blame for any confusion that may arise from the "persistent difficulties with, and misunderstandings of, the definitions of the Commissionís dosimetric quantities" referred to by Chairman Clarke.