|Comments on the draft of ICRP 2005 Recommendations
1. Comment on “radiation weighted dose”
It is suggested in the draft recommendations that a new term “radiation weighted dose” is proposed instead of the equivalent dose to define the organ or tissue dose for risk evaluation of its stochastic effects and a new special unit for this quantity is being considered. This quantity can be regarded as an intermediate product to calculate the effective dose and is never used itself except for some limited situations such as estimation of thyroid cancers in nuclear accidents. For this reason, we think that any terms or units incurring confusion should not be given to the organ dose for stochastic risk estimation. On the other hand, doses in a tissue or organ should play an important role in the risk estimation of deterministic effects and accordingly a quantity with the special unit “GyEq” is proposed for this purpose. This proposal is scientifically quite reasonable.
2. Comment on units of doses
It is criticized even now that the doses and their units for radiation protection are so complicated that a lot of people, even some radiation protection experts, have difficulties in understanding and using them correctly. We do not believe that the introduction of new name of quantity or unit improves the present difficult situation. It would rather extend the current confusion. We propose a clear-cut usage of dose units that “Gy” or “GyEq” is assigned to the dose for deterministic effect estimation and “Sv” to the dose for stochastic effect estimation, namely the effective dose.
3. Comment on determination of wR values for neutron
Some values of wR for neutron were determined in the draft as a human body averaged mean quality factor qE calculated on the basis of the Q(L) relationship, since there is little reliable RBE data for human at present. This half measure can be understood because there is no better alternative solution. However some scientific reasons should be given for an adjustment of multiplying qE by the factor of 1.6 in Eq (3) and the scientific reference paper should be given for reducing the maximum wR value to 20 for neutrons at around 1 MeV. Some evidence papers should be referred for the descriptions: “RBEhigh-LET=25 from animal data” (paragraph 71) and 2 in the energy range between 5 to 150 MeV. This would result in an increase of wR for neutrons between 22% and 39% relative to the data of the continuous function as defined in Publication 60” (paragraph 73).
4. Comments on insistence of wR
The concept of wR was introduced in Publication 60, since the Q(L) relationship was often interpreted to imply a spurious precision. However, the Q(L) relationship play an important role in the determination process of numerical values of wR because of the lacking of RBE data for human. Especially for neutron, the wR value was determined from the qE values based on the Q(L) relationship. We agree that the introduction of wR allows us to calculate dose conversion coefficients easier and simpler, but only a few scientists are involved in the calculations, and almost all people just use their results. Hence, we cannot find any reasons for insisting the use of wR – a simplified weighting method of radiation qualities based on the Q(L) relationship, and such simplicity does not help anyone and just makes confusions. If ICRP still insists to use this wR concept, it should clarify the reason again.
5. Comment on quantity for annual dose limit of tissue
The annual limits of doses in a tissue or organ are shown in Table 9. This limit should be applied only for preventing the deterministic effects, and hence, their unit should be “GyEq”.
6. General comments
We think that ICRP has two roles; one is to investigate and review the scientific data, and the other is to make judgments on issues related to radiation protection as experts’ opinions. However, the mixture of two roles – “scientific review” and “expert’s opinion” – in one sentence or paragraph sometimes makes confusions. We therefore demand ICRP to clarify the distinction between “scientific review” and “expert’s opinion” in the document. The references that show the scientific data used in the judgments should be shown in the document to verify the objectivity and reliability of the judgments.