**Re: ICRP XXX (2012) Occupational Intakes of Radionuclides**

Dear collegues,

this is a proposal for two corrections of the terminology used in the draft ICRP report XXX (2012) on Occupational Intakes of Radionuclides. The proposal comes from the members of the German Committee of Radiological Standards (Normenausschuss Radiologie, NAR), Dr. Ambrosi, Dr. Kapsch, Prof. Kramer and myself, and is supported by Prof. Breckow, president of the German-Swiss Society of Radiation Protection (Fachverband für Strahlenschutz), and by Prof. Dietze, member of ICRP Committee 2. We express our high estimation of the ICRP and want to give our advice in the tradition of friendly relationships that has always guided the German members of the ICRP main commission, subcommittees and task groups.

Our concern is the long-term stability of ICRP terminology in an important definition of radiation protection. We are referring to the basic definition

(formula - see ICRP 60 pg, ICRP 103 p 23) (1)

(ICRP 60, page 5; ICRP 103, page 23) which expresses that the "equivalent dose in a tissue or organ, H_{T}" is the weighted sum of the mean absorbed doses D_{T,R} in the tissue or organ T, with radiation weighting factor w_{R}. This definition, introduced in ICRP 60 and maintained in ICRP 103, has been entered into international legislation, standards and textbooks, and it has achieved particular importance by its worldwide use to define the effective dose, the w_{T}-weighted sum of the equivalent doses to the tissues or organs, the quantity in terms of which the fundamental radiation protection dose limits for workers, the population and emergency cases are expressed. However, in the draft ICRP XXX (2012) on Occupational Intakes of Radionuclides, this definition has been changed to read

(formula - see draft report, page 11) (2)

(ICRP XXX, page 11) where r_{T} is a "target region" in the Reference Adult Male or Female used for dose calculations by application of the absorbed fraction concept, or a region in a voxel phantom applied to calculate equivalent doses from external exposure. Moreover, H(r_{T}) is here sometimes called "equivalent dose", while the specifier "to a tissue or organ" is lost.

**a) Proposal concerning the maintenance of the symbol H _{T}:** We acknowledge that the symbol r

The undesirable effects that would follow ICRP's change from the previously recommended eq. (1) towards the recommendation of eq. (2), namely a) of giving the impression of some instability of the ICRP definitions, b) the need of rewriting this equation in numerous laws, regulations, textbooks and public informations and c) the need to prohibit the foreseeable misunderstandings following from this change, could be avoided by positioning the transition from the r_{T} to the T notation at an earlier stage in the evolution of the ICRP XXX (2012) equations, namely at the key equation

(formula - see draft report, page 98) (3)

(ICRP XXX, page 98) which expresses , the time-dependent equivalent dose rate in an organ or tissue T, by A(r_{s},t), the time-dependent activity in the source regionr r_{S,} and S(r_{T}←r_{S}), the conversion factor based on the absorbed fraction in the target region r_{T} and other factors including w_{R}. Eq. (3) would then describe the typical approach of committed organ equivalent dose rate calculations, and in all equations following from eq. (3) - starting with the expression for the committed equivalent dose H_{T}(T_{D}) as the time integral of - the index T could then be applied in the hitherto conventional way. The advantage of introducing index T already at this stage is that eq. (3) is adressing the specialists using it, who understand the details and who will have anyway to anticipate formal changes in the present stage at which the ICRP and MIRD terminologies are merged, whereas eq. (1) is for international use in laws, regulations and textbooks, i.e. for a worldwide readership.

**b)** **Proposal concerning the maintenance of the specifier "to a tissue or organ" in the name of quantity H _{T}: **The importance of stating the name of the organ or tissue for which values of quantity H

In summary, our proposals to ICRP are a) to continue recommending the long-standing definition of the "equivalent dose to a tissue or organ" in the form of eq. (1) and to write eq. (3) in the indicated way, thereby introducing the term H_{T} already at the technical stage of the sequence of formulae, and b) to maintain the specifier "to a tissue or organ" for the sake of clarity. Hoping on your understanding and with all good wishes for the success of ICRP,

yours sincerely

Dietrich Harder

Former member of the ICRU,

Former chairman of the German Radiation Protection Commission.

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